Online newspaper of professor Yasser Metwally

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 31, 2009 — We are continually surprised by the variety of tumors that occur in the region of the pineal. No other region of brain shows so many pathologic tumor types. The most widely used pathologic classification is :(1) teratomas (includes all germ cell tumors), (2) pineal cell tumors (pineocytoma and pineoblastoma), (3) glial neoplasms, and (4) cysts,and meningioma

Pineal region tumors are more common in Japan than in the Western Hemisphere, because of an inordinately high frequency of germ cell tumors. Pineal tumors account for less than I per cent of intracranial tumors in the Western Hemisphere, but in Japan account for about 7 to 10 per cent (2 per cent teratomas, 4.5 per cent germinomas).

Table 1. Pineal region tumours (Click on table to enlarge)

• Teratoma and Germ Cell Tumors

The most complex tumors are the germ cell tumors. Extragonadal germ cell neoplasms are presumed to arise from rests of germ cell tissue left behind during embryogenesis. They occur principally in children and young adults in midline sites throughout the body, including the sacrum, mediastinum, pineal, and suprasellar regions .The histology of germ cell tumors is identical in all sites of origin, but the sex ratio and individual tumor types vary depending on the location. For example, pineal germ cell tumors occur almost exclusively in male patients, whereas suprasellar germ cell tumors display close to a 1:1 male to female ratio . This pattern has been seen in numerous studies and remains unexplained. Pineal tumors are often mixed, containing several germ cell elements.

Figure 2. MRI T2 image [left] and T1 image precontrast [right] showing a pineal region teratoma. The T2 hypointensity and T1 hyperintensity is due to blood products , increased fat content or calcification

A primordial germ cell gives rise to a tumor that is called a “germinoma.” This tumor, which is histologically identical no matter where it arises, is named according to the organ of origin; seminoma in the testes, dysgerminoma in the ovary, and germinoma elsewhere.Germinomas and seminomas seem to be biologically similar; both tumors, are highly malignant but quite sensitive to radiation therapy.

Figure 3. Precontrast CT study [left] and MRI T1 pre,postcontast [right] showing a pineal region germinoma

A primitive germ cell may also lead to a malignancy that is called an embryonal carcinoma. This tumor is highly malignant but may nevertheless give rise to a differentiated neoplasm of embryonic tissues called a teratoma that is a benign and slow-growing tumor, with elements derived from all three germ cell lines (ecto-,endo-,and mesoderm). Some embryonal carcinomas contain elements of teratoma and are termed teratocarcinomas.

Table 2. Germinomas and teratomas (Click on table to enlarge)

An embryonal carcinoma cell is believed to be a precursor malignancy that can also differentiate into a tumor of extraembryonic tissue. If the resulting tumor contains trophoblastic tissue, it is called a choriocarcinoma; if it contains yolk sac elements, it is called an endodermal sinus tumor (EST) or yolk sac tumor. Both choriocarcinoma and endodermal sinus tumors are highly malignant and are virtually incurable when they originate intracranially.A primordial germ cell gives rise to a tumor that is called a “germinoma.” This tumor, which is histologically identical no matter where it arises, is named according to the organ of origin; seminoma in the testes, dysgerminoma in the ovary, and germinoma elsewhere.Germinomas and seminomas seem to be biologically similar; both tumors, are highly malignant but quite sensitive to radiation therapy.

• Biologic Markers

Germinoma, teratoma, embryonal carcinoma, choriocarcinoma, endodermal sinus tumors, and mixed tumors are found in the pineal region. Some germ cell tumors produce proteins that can be used to diagnose the presence of a particular cell type and may also monitor growth or regression of tumor .

• Beta Human Chorionic Gonadotropin

Human chorionic gonadotropin (HCG) is a glycoprotein hormone, normally produced by the placenta. It is synthesized and secreted in large quantities by normal trophoblastic tissue or choriocarcinomas. Low levels of HCG may be elaborated by nonplacental tumors, particularly gonadal, hepatic, or gastric neoplasms.

HCG is composed of two nonidentical subunits. The alpha subunit is identical to the alpha subunit of the other gonadotropins [luteinizing hormone (LH) and follicle-stimulating hormone (FSH)]. The beta subunit is immunologically distinct. Beta human chorionic gonadotropin (PHCG) contains 139 amino acid residues and PLH . Although PHCG and PLH share identical residues in positions I to 112, the C-terminal residues differ. Radioimmunoassay for the beta subunit can detect minute quantities of HCG and can differentiate it from LH; this method has been applied to the CSF.

• Alphafetoprotein

Alphafetoprotein (AFP) is a 65,000 to 70,000 dalton protein made in large quantities by fetal liver and yolk sac. Plasma concentrations of AFP reach 60 mg per ml at 30 weeks of gestation, and amniotic fluid concentrations reach 425 to 1500 ng per ml at 32 weeks of gestations. The adult plasma level of I to 2 ng per ml is achieved by 2 years of age. Endodermal sinus tumors always produce AFP, and glandular tubules of this tumor contain eosinophilic material that stains immunocytochemically for AFP.

• Pattern of Biologic Markers Produced by Various Germ Cell Tumors

With central nervous system (CNS) tumors, CSF levels of biomarkers may be more sensitive and precede elevations in serum.HCG is always produced by choriocarcinomas, and AFP is always produced by endodermal sinus tumors. Embryonal carcinomas are pleiomorphic: they may produce HCG, AFP, both, or neither, depending on their degree of differentiation. Mature teratomas are differentiated tumors that do not elaborate markers, but immature teratomas may occasionally produce AFP.Likewise, germinomas generally do not produce markers, but some germinomas produce HCG because there are syncytiotrophoblastic giant cells (SGC) in the tumor.

Biomarkers in blood or CSF are a good indicator of specific germ cell tissues even when the critical cells are not seen in the pathologic specimen . In the absence of liver disease, AFP is a reliable marker of EST or embryonal carcinoma. the elevated AFP was (in retrospect) an indicator of the presence of embryonal carcinomatous elements of a mixed germ cell tumor. An elevated AFP should prompt scrutiny of the pathologic specimen for EST or embryonal carcinoma elements. High levels of PHCG, exceeding 10,000 mlU per ml, are generally not seen in germinomas, even those containing SGCS, and suggest the presence of choriocarcinoma elements.

• Pineal Parenchymal Tumors
  • Pineocytoma

A pineocytoma is composed of cells that resemble mature pineocytes and are arranged in a glandular pattern. In contrast, pineoblastoma is histologically identical to medulloblastoma and is considered a primitive neuroectodermal tumor occurring in the pineal region.

Although pineocytoma appears to be a differentiated tumor, it may behave like pineoblastoma, seeding the CSF pathways. Both pineocytoma and pineoblastoma are malignant, responding to radiation, but tending to recur They show no sex predilection.

GLIAL CELL TUMOURS

• Gliomas

Glial tumors make up the about one third of pineal region tumors .Two thirds of the glial neoplasms are malignant, but one third are benign and surgically resectable. Most benign tumors are cystic astrocytomas, clinically similar to juvenile cerebellar astrocytomas, .oligodendrogliomas are usually slowly growing

Malignant gliomas of the brain stem may start in the pineal region; obstructing the aqueduct early if they originate in the midbrain, or if exophytic components project into the quadrigeminal cistern. These tumors, like gliomas of the cerebrum, vary in malignancy and sensitivity to radiotherapy. True glioblastomas are rapidly lethal, usually causing death in less than I year.

• Meningiomas

Pineal region meningiomas are tumors of middle age that show no sex predominance and are fully resectable.

Figure 4. Postcontrast CT scan [left] and precontrast MRI T1 image [right] showing a pineal region teratoma,notice the vascular rim [arrow]

Other tumors we have seen included spindle cell sarcoma, choroid plexus papilloma, hemangioblastoma, and progonoma (a melanocytic neuroectodermal tumor). Chemodectomas presumably arise from sympathetic fibers that innervate the gland. Not every mass in the pineal region is a neoplasm,as tuberculomas are occasionally found in this region.

TERMINOLOGY IN PINEAL REGION TUMOURS

We avoid the term pinealoma and prefer the simple description pineal region tumor for all tumors that are found in this region. “Pinealoma” is misleading in two ways. It causes confusion with pineocytoma, and implies that the tumor is a neoplasm of pineal cell origin, which is actually one of the least common neoplasms in this region. Second, the term conveys the impression that all tumors in the pineal region are alike and that their proper management is identical.

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 30, 2009 — Haemorrhagic microvascular brain disease constitutes the other facet of the bad coin (the microvascular brain disease) the first facet of which is the ischemic microvascular brain disease. Both the hemorrhagic and the ischemic microvascular brain disease share common haemorrheological, metabolic endocrinal abnormalities and cardiac changes(LVH).

In microvascular brain disease, the small penetrating arterioles of the subependymal and the pial microvascular systems tend to become stenosed and undergo lipohyelinosis or they may dilate to form microaneurysms . From the pathological point of view both Lipohyelinosis and microaneurysms, almost invariably, coexist in the same individual, thus making the patient Liable to develop either the ischemic or the hemorrhagic microvascular brain disease.

MICROANEURYSMS OF THE SMALL PENETRATING ARTERIOLS

Microaneurysmal formation occurs predominantly in the territory of the subependymal microvascular system, thus making the incidence of the hemorrhagic microvascular events much more frequent in the periventricular grey matter (thalamus, basal ganglia and the internal capsule) or the immediate periventricular white matter.

Figure.  1.The microaneurysm

Figure 2.  Common sites of microaneurysms

Microaneurysmal formation should weaken the arteriolar wall so that rupture and leakage can occur even in normotensive states. When microaneurysmal rupture occurs, the bleeding will result in hematoma formation. The bleeding will then be arrested by occlusive thrombosis of the bleeding microaneurysms. Following microaneurysmal rupture and bleeding, the size of the resulting haematoma will be determined by the bleeding time. The bleeding time is a function of the whole blood viscosity in general and the platelet agreggability in particular.

Should microaneurysmal bleeding occurs during periods of higher blood viscosity, the bleeding time will be shorter and subsequently the size of the resulting haematoma will be smaller. In fact during high blood viscosity the bleeding is not infrequently arrested before forming hemorrhages adequate to give rise to immediate clinical sequelae. Patients with higher blood viscosity and thrombotic tendency, although less likely to develop serious hemorrhagic microvascular events, they are particularly liable to develop serious ischemic microvascular events.

During periods of lower blood viscosity and thrombotic tendency of the blood, microaneurysmal bleeding might result in huge haematoma formation that may split along the planes of the white matter forming a substantial space occupying clot, or may rupture into the ventricular system resulting in massive ventricular haemorrhage. In general inverse correlation is present between the haematoma size and the current blood viscosity at the time of microaneurysmal bleeding

Patients with microvascular brain disease might have recurrent events which could be purely hemorrhagic or purely ischemic, however, it is not uncommon for some patients to fluctuate between the hemorrhagic and the ischemic events, developing hemorrhagic events at some times and ischemic events at another times. In general ischemic microvascular events are much more common and much more frequent than the hemorrhagic events.

• Pathology :

Cerebral Haematomas occur much more frequently at the putameno-capsular and the thalamic regions and may rupture into the ventricular system. Less common sites include the cortical and the immediate subcortical white matter, especially in the parietal region, the pons and the cerebellum.

The resulting haematoma is dark red in color due to the existence of deoxyhaemoglobin inside the intact RBCS. During the subacute stage (3days – one month) the dark red color of the haematoma is replaced by a brownish discoloration, which starts at the periphery of the haematoma and then extends to its center. This brownish discoloration occurs due to the replacement of deoxyhaemoglobin by the oxidized methemoglobin.

• Subacute hematoma

Gradually the haematoma is surrounded by reactive gliosis and macrophages laden with hemosiderin granules (Ferric hydroxide). The clot is gradually absorbed starting with its periphery and is replaced by a yellow fluid, this is called an apoplectic cyst. Reactive gliosis progressively increases and ultimately transforms the haematoma into a slit-like scar.

Pathologically the brains of patients with cerebral hemorrhages very frequently show evidence of past microvascular ischemic events such as lacunar infarctions,leukoaraiosis,etc

STRUCRURAL NEUROIMAGING OF MICROVASCULAR CEREBRAL HEMORRHAGE

• CT scan

A cerebral haematoma in the acute stage has higher attenuation values (hyperdense). The higher attenuation values of fresh blood is due to the existence of packed hemoglobin in the haematoma. With progressive absorption of hemoglobin, (this usually starts from the periphery of the haematoma) the attenuation value of the haematoma gradually decreases until the high density haematoma is replaced by a low density space occupying cyst.

Figure 4. Precontrast follow up CT studies that showed the progression of the haematoma from a hyperdense lesion [acute]to a hypodense lesion [subacute] to a slit-like scar [chronic]

The evolution of the haematoma from a high density clot to a low density cyst usually takes a period that ranges between one month to three months. The walls of this cyst might enhance and the haematoma at this stage might be mixed with abscess or glioma. History is of paramount significance at this stage. Very old haematoma appears by CT scan as a slit-like hypodense area with negative mass effect.

In general Haematomas are space-occupying with positive mass effect and are commonly surrounded by a hypodense edema area. The most common sites are the putameno-capsular and the thalamic sites and either of them might rupture intraventricularly. Less common sites includes the parietal lobe, pons and cerebellum

• MRI in cerebral haemorrhage.

Imaging of haematoma by MRI is time dependent as follow

• The acute stage (0 – 3 days)

Due to the presence of the magnetically susceptible deoxyhaemoglobin. The T2 relaxation time will be markedly shortened, so that fresh blood appears hypointense (black) on the T1weighted MRI images. This hypointensity is commonly surrounded by a wider hyperintense area that represents edema. On the T1 weighted images fresh blood appears isointense or slightly hyperintense

Figure 5. Acute haematoma ,MRI T2 image ,the central hypointensity relates to the intracellular deoxyhaemoglobin

• The subacute stage (3 days – one month)

The picture of haematoma, during this period is governed by the progressive reduction in the concentration of deoxyhaemoglobin and the progressive increase in the concentration of the oxidized methemoglobin. These changes take place from the periphery of the haematoma to its centre.

Progressive reduction in the concentration of deoxyhaemoglobin results in progressive disappearance of the T2 hypointensity observed in the acute stage. Absence of the deoxyhaemoglobin will result in progressive prolongation of the T2 relaxation time that starts from the periphery of the haematoma to its centre, this results in progressive increase of the T2 signal intensity (it becomes brighter); At first the periphery of the haematoma becomes brighter on the T2 weighted images, and this brightness progressively extends to the centre.

Because the oxidized methemoglobin has a paramagnetic quality it results in shortening of the T1 relaxation time, so that the haematoma in the subacute stage appears hyperintense (bright) on the T1 weighted MRI images. This again starts from the periphery of the haematoma and progresses to its centre, because as mentioned before methemoglobin starts to appear at the periphery of the haematoma,this results initially in ring hyperintensity on the T1 images

Figure 6. Subacute haematoma ,notice the peripheral hypointense rim on the T2 and proton density images that corresponds to hemosederin and the hyperintense rim on the T1 image that corresponds to methaemoglobin

• Chronic stage (one month to 3 months):

Figure 7. Precontrast MRI T1 showing the chronic hematoma as a diffuse ly hyperintense space occupying lesions (methaemoglobin)

Table 1. Biochemical stages of cerebral hemorrhage (Click to download table in PDF format)

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 11, 2009 — Direct evidence of a meningioma may be discerned from plain skull films in a remarkably high percentage of patients. in one-half of patients harboring meningioma the diagnosis could be made radiologically, The cardinal signs of meningioma are: [1] hyperostosis, [2] increased vascularity, and [3] tumor calcification. It is our belief that the presence of any one of these cardinal signs properly observed and evaluated can be adequate for the diagnosis of meningioma. Any two in combination or any one together with evidence of increased intracranial pressure can reliably establish the diagnosis of meningioma.

In general hyperostosis and enlarged vascular marking are much more likely to occur in the syncytial or angioblastic meningiomas,while calcifications are much more likely to be found in the transitional or psammomatous meningioma types

• Hyperostosis

Hyperostosis is the first and most frequent direct evidence of meningioma. The new bone formation occurring in the neighborhood of a meningioma is a reactive change in the skull and not an integral part of the tumor.The exact mechanism of hyperostosis is not well understood ,however it is necessary for tumor cells to invade the overlying bone to invoke hyperostosis, the density of the change found in some cases and the difficulty of identifying tumor cells in the densely hyperostotic area may denote a bone reaction out of proportion to the quantity of invading tumour cells.

Figure 1. Postcontrast CT scan [left] CT scan bone window [middle] and plain x ray [right] showing bone hyperostosis and increased vascular marking

The inner table of the skull, the diploic space,and the outer table all may be involved in the hyperostotic process. In any given case, any one alone of these portions of the skull may be most conspicuously involved or multiple areas may be implicated. The inner table, however, is by far the most common cranial layer to be affected

Figure 2. Postcontrast CT scan [left] CT scan bone window [middle] and plain x ray [right] showing bone hyperostosis and increased vascular marking

The hyperostotic process takes place through the laying down of bone in multiple sheets parallel to the plane of the tabular cortex. In radiographs, the changes involving the inner table will appear as an area of extra density when viewed face on, whereas in tangential view the change will present as an enostosis. In the en face projection, the density will obscure normal bony architecture in the area of thickening, whereas the tangential view will demonstrate the intact nature of the diploic space and outer table if the hyperostosis is isolated.

Isolated hyperostosis of the inner table of the skull is most common in the presence of meningioma of the cerebral convexity and parasagittal areas.True alteration of bony architecture usually occurs with involvement of the diploic space. It may become only hypertrophied with preservation of the spongy architecture. More often, however, obliteration of the spongy appearance takes place through the deposition of large amounts of compact bone within the diploic area. Hypertrophy of the diploe may be related to increased vascularity within it, whereas sclerosis may be related to the infiltration of the Haversian system

Involvement of the outer table with the production of an external mound of bony tissue(and often a clinically detectable mass) may be seen but is most common in the thin portions of the skull where the inner and outer tables are in close approximation. Thus, although it is uncommon for a palpable mass to be present in the case of convexity meningiomas, exophthalmos is an expected finding in patients with meningioma of the sphenoid ridge. Such flat tumors, lying along the sphenoid ridge where there is essentially no diploic space, result in a marked bony thickening along both the inner and outer tables,

• Enlarged meningeaL vascular markings

The second of the cardinal manifestations of meningioma is increased vascularity. This change occurs essentially as frequently as hyperostosis and, when properly evaluated, its significance can be just as important. The increase in vascularity takes two different forms: (1) an area of localized increased vascularity, hypervascularity, or neovascularity of the bone in the area of the tumor,and (2) enlargement of the vascular channels either supplying or draining the tumor area. The latter occurs more commonly than the former, but neovascularity is considered a much more specific change. Statistics regarding altered vascularity occurring in plain skull films are of little significance, however ,since , for the most part only those tumors occurring in distal areas provide the opportunity for such changes to be visualized. Thus, the great majority of tumors exhibiting abnormal vascularity are those of the cerebral convexity and parasagittal areas.

With basal tumors, visualization of the blood supply of the tumor in plain films is infrequent, even though it may be as abundant as in the case of tumors of the vault. Neovascularity may occur in only a small area beneath the tumor and be significant. More often, however, the hypervascularity presents a rounded or oval pattern, measuring several centimeters in diameter. The basic gross pathologic change is the perforation of the skull by many small arteries and veins extending to and from the tumor. The development of this neovascularity results in the presence of a multitude of small punctate radiolucent areas, a condition that is often referred to as stippling. Occasionally, stippling alone will be present beneath the tumor, and for all practical purposes it may be considered a diagnostic sign of meningioma.In the majority of cases, however, other changes will be found in the general vascular pattern, and it is common to find hyperostosis in association with a localized patch of neovascularity

Enlargement of the meningeal vascular channels occurs even more often than stippling, and,in the majority of instances when stippling is found, enlargement of the meningeal vascular channels is present also. The most frequent and important changes occur along the course of the middle meningeal artery; the anterior and posterior meningeal arterial pathways are less conspicuous radiologically. The two basic changes that occur in the middle meningeal groove,which carries both the meningeal artery and veins, are: (1) unilateral enlargement of the main vascular channel and (2) abnormal branching.

Evidence of enlargement may be found at the point where the middle meningeal artery enters the skull through the foramen spinosum. The foramen can be oval as well as round.,The established range of normal for the shorter diameter of the foramen spinosum is between l.5 and 3 mm, with an average of 2 mm, as seen in basal radiographs of the skull. However, considerable variation on the two sides often occurs and it is not uncommon to find a larger foramen spinosum even on the side opposite the tumor. By itself, therefore, the presence of a large foramen spinosum cannot be considered a reliable diagnostic finding. A more consistent abnormality is widening and tortuosity of the channel of the middle meningeal artery as it crosses the floor of the middle fossa.The groove courses forward and lateralward from the foramen spinosum to the lateral edge of the greater sphenoid wing before ascending onto the vault. The size and configuration of the channel can be assessed on basal skull radiographs; the channel is enlarged with basal meningiomas and meningiomas of the sphenoid ridge.

Great importance can be attached to the appearance of the main middle meningeal channel as it courses upward and backward over the vault of the skull. An enlarged channel may maintain a straight course, but in other instances it may be unusually tortuous. Tortuosity of this vascular groove is an important radiologic change often found in patients with meningioma, and it usually denotes enlargement and elongation of the artery.

A slight degree of tortuosity of the middle meningeal groove is not uncommon in normal cases, but mostly in the initial portion of the trunk of this artery as it begins its ascent in the region of the greater wing of the sphenoid. In the normal case, the tortuous segment is short, 1-2 cm in length,and in the majority of instances is not associated with any suspicious increase in the width or prominence of the groove. In the lateral view, an enlarged meningeal channel appears as a wider,deeper (and therefore darker) shadow, and more sharply marginated than normal, or as compared with the groove on the opposite side.

The enlarged channel often remains of evenly increased diameter until the level of the tumor on the vault is reached, rather than tapering or narrowing as it arborizes.

The most important feature of enlargement of the middle meningeal channel itself is unilaterality. Whenever there is a discrepancy in appearance, with one middle meningeal channel more conspicuous in either the frontal or stereoscopic lateral radiographs, the case must be regarded with high suspicion. Some normal variation does occur, but, unfortunately, the absolute limits of normal and the normal range of dissimilarity of the middle meningeal channels on the two sides are not well defined. When only the main channel is prominent on one side,it is to be expected that in a fairly sizable group of patients no clinical or other evidence of intracranial disease will be found. However,whenever asymmetry exists, it is incumbent upon the neurologist to make a very careful search tor other evidence of intracranial disease,routinely through the careful study of the ordinary projections and also through study of additional views as required, particularly additional stereoscopic pairs of films.

It must also be kept in mind that both middle meningeal vascular grooves may be enlarged, and, under these circumstances, both may be quite conspicuous but relatively symmetrical. Meningiomas of the falx and of the parasagittal areas are the most frequent to invoke such a bilateral change and bifrontal tumors may also result in symmetrical enlargement .

Another significant alteration in the middle meningeal vascular channel that favors the diagnosis of meningioma is abnormal arborization.As visualized radiologically, the main channel of the middle meningeal artery courses upward and slightly backward posterior to the coronal Suture, and the great majority of normal branches seen are posterior ones which course upward and backward over the surface of the parietal bone. Although some normal anterior branches are present, they usually do not cause conspicuous markings or grooves in radiographs. Whenever anterior branches of a middle meningeal artery are found extending forward over one side of the vertical portion of the frontal bone, we tend to regard them with suspicion. In these cases, a careful search should be made at the termination of the rostral meningeal branch for evidence of other local changes such as stippling or hyperostosis which might confirm the suspicion of meningeal tumor or for evidence of increased intracranial pressure.

In general, it may be stated that whenever a branch is conspicuously larger than an adjacent groove from the same parent vessel, it should be regarded as highly suggestive of an abnormality.Posterior branches of unusual size are also to be regarded with question. For the most part, such abnormal vessels arise from the main middle meningeal trunk and extend to the parietal convexity or the parietal parasagittal region, the chief normal posterior branch of the middle meningeal usually arises from the main vessel along the base of the skull.Its groove frequently can be seen coursing upward across the temporal squama and then curving backward to spread out over the posterior half of the parietal bone and even into the occipital area. However, the secondary and tertiary subdivisions of the posterior branch of the middle meningeal artery are not ordinarily as conspicuous in radiographs as are the branches of the main trunk. The posterior branch may be enlarged with meningioma and also with certain other vascular lesions of the posterior regions,such as an arteriovenous malformation.

Venous enlargement in the diploic space often is a more difficult finding to evaluate than changes in the arterial channels. The diploic veins form a generally constant pattern anatomically, extending downward over the vault and communicating freely with intracranial venous structures as well as extracranial ones through emissary foramina. Radiologically, however, the veins appear less constant and there is considerable variation between patients with regard to the prominence or conspicuous nature of various diploic trunks. The diploic veins have been a popular subject of study for many years and there is considerable radiological literature concerning their appearance. Generalized prominence of the diploic veins usually is not of pathological significance. Some skulls are extremely vascular to the extent that the term “phlebectasia” has been coined to describe them. The main clinical significance of such a finding is troublesome bleeding that may develop with intracranial surgery in such cases

• Tumor calcifications

The third cardinal finding for the diagnosis of meningioma is tumor calcification. Its occurrence has been reported variously.Most authors observers have described an incidence of something less than 10%.The extent of calcification shows marked variation radiologically, just as it does pathologically. The most common type of calcification evident is a cloudlike, globular shadow of increased density resulting from the conglomeration of multitudes of psammoma bodies.

Figure 5. Plain x ray skull [right] showing a heavily calcified transitional parasagittal meningioma

In some instances, the entire tumor may be fairly evenly opacified . At other times,the calcification appears to occur predominantly about the tumor margin or in one quadrant of the tumor Thus, the plain films may reveal not only the identity of the tumor but its extent without the necessity of contrast study. A radiograph of the pathologic specimen often will allow superimposition of the tumor shadow on the radiograph of the living subject.In some tumors, unfortunately, the calcification is of nonspecific type rather than a homogeneous conglomerate collection of psammoma bodies. Branching plaques of calcium may be present which resemble calcification in granulomas or glial tumors. In other instances, true bone may be formed, as may occur with other degenerative changes. In our experience, conglomerate psammoma calcification is the type encountered in the majority of instances.

Figure 6. CT scan studies showing heavily calcified meningiomas

There appears to be no special site of predilection for the development of fibrous meningiomas exhibiting calcific changes. Such tumors are encountered arising along the vault, particularly parasagittally, in the region of the tuberculum sellae and in the floor of the middle fossa. It is doubtful that the limited number of calcified tumors available to any one observer would contradict the general incidence of global, fibrous tumors arising in various sites.

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 10, 2009 — The tumour is often rounded and well-defined. Density before contrast ranges between slightly hyperdense [syncytial type] to markedly hyperdense [transitional type]. The tumour has a positive mass effect and commonly surrounded by edema, which is more common in the highly cellular syncytial type. Cystic changes are occasionally observed in the syncytial type. Calcification is frequently observed in the transitional type, it ranges between punctate, patchy and diffuse. Bone hyperostosis is much better appreciated by CT scan, being more frequent in the syncytial type.  After contrast injection, the tumour commonly shows dense and diffuse enhancement.

CT SCAN CORRELATION WITH THE MAIN PATHOLOGICAL TYPE

• Fibrous and transitional type

Figure 2. CT scan study precontrast [left] and postcontrast study [right] showing a heavily calcified transitional meningioma with dense enhancement.

• Syncytial meningioma

Figure 3. Syncytial meningioma

Figure 4. CT scan precontrast [left] and postcontrast [right] showing a diffusely enhanced, syncytial parasagittal meningioma.

• Angioblastic meningioma

Figure 5. Postcontrast CT scan study showing an angioblastic convexity meningioma

SOME COMMON ANATOMICAL SITES FOR MENINGIOMAS

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 10, 2009 — Precontrast and postcontrast MR imaging studies can easily diagnose meningioma as well as CT; however, MR imaging can also predict histologic subtypes of meningioma. Metwally [1] reported a strong correlation between tumor histology and tumor intensity on T2-weighted images compared with those of the cortex. Meningiomas are classified into four basic subtypes: fibroblastic, transitional, syncytial, and angioblastic.

• MRI picture of Fibroblastic meningiomas

Fibroblastic meningiomas are composed of large, narrow spindle cells. The distinct feature is the presence of abundant reticulum and collagen fibers between individual cells. On MR imaging, fibroblastic meningiomas with cells embedded in a dense collagenous matrix appear as low signal intensity in Tl-weighted and T2-weighted pulse sequences.

Figure 1. Transitional meningioma with the characteristic psammoma bodies

• MRI picture of transitional meningiomas

Transitional meningiomas are characterized by whorl formations in which the cells are wrapped together resembling onion skins. The whorls may degenerate and calcify, becoming psammoma bodies. Marked calcifications can be seen in this histologic type. MR imaging of transitional meningiomas thus also demonstrates low signal intensity on Tl- weighted and T2-weighted images, with the calcifications contributing to the low signal intensity

Figure 2. Transitional meningioma

• MRI picture of Syncytial meningioma

Syncytial (meningothelial, endotheliomatous) meningiomas contain polygonal cells, poorly defined and arranged in lobules. Syncytial meningiomas composed of sheets of contiguous cells with sparse interstitium might account for higher signal intensity in T2-weighted images. Microcystic changes and nuclear vesicles can also contribute to increased signal intensity.

Figure 3. Syncytial meningioma, histopathological picture (A) and MRI picture (B)

• MRI picture of Angioblastic meningiomas meningioma

Angioblastic meningiomas are highly cellular and vascular tumors with a spongy appearance. Increased signal in T2-weighted pulse sequence of these tumors is due to high cellularity with increase in water content of tumor.

Thus based on the correlation between histology and MR imaging appearance of meningiomas, Metwally [1] have concluded that meningiomas significantly hyperintense to cortex tend to be primarily of syncytial or angioblastic type, whereas meningiomas hypointense to cortex tend to be primarily of fibrous or transitional type. Heterogeneous appearance of meningiomas in T2-weighted pulse sequence can be due to tumor vascularity, calcifications, and cystic foci.

Grossly meningiomas are characterized, by the existence of a vascular rim that surround the meningioma and appear signal void on both T1,T2 MRI images,this finding is consistent with the overall blood supply of meningiomas [the periphery of meningiomas is supplied by branches from the anterior or middle cerebral arteries that encircle the tumour and form the characteristic vascular rim] .Meningiomas are also characterized by the existence of a hypointense cleft between the tumour and the brain that probably represents blood vessels or a CSF interface .Other characteristic,feature is the existence meningeal tail on the enhanced T1 images.The tail extends to a variable degree away from the meningioma site and probably represent a meningeal reaction to the tumour. In general meningiomas tend to enhance brightly following injection of contrast material.

Figure 5. The hypointense cleft between the tumor and the brain (A,B) and the meningeal tail (C)

MR imaging has also been found to be superior to CT in evaluating meningiomas for venous sinus invasion or internal carotid artery encasement Brain edema is observed in about 50% of meningiomas, with severe edema occurring with syncytial and angioblastic types.

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 9, 2009 — Tumors of the meningioma group are usually very vascular and often produce enlargement of the arteries that supply them. The most characteristic vascular finding of a meningioma is a contribution to the blood supply of the neoplasm by branches of the external carotid system. Whenever it is possible to show that the external carotid artery shares in the blood supply of an intracranial tumor, it is most likely to be a meningioma. On the other hand, cranial tumors that invade the meninges may have an evident blood supply in the angiograph from a branch of the external carotid artery; however, bone destruction is usually also evident. Metastatic tumor invading the bones or the meninges and even gliomas that become exophytic may exhibit such a finding.

Table 1. Click on table to enlarge

• Enlarged vascular supply

With a meningioma, the artery that most often becomes enlarged is the middle meningeal (or its branches) and the other meningeal arteries.

Figure 1. The sunburst appearance and enlarged vascular supply

After a meningioma has evoked a reaction of the outer periosteum of the skull, the superficial temporal , or some other extracranial branches of the external carotid artery will participate in the tumor blood supply. In attempting to determine whether the external carotid artery is indeed involved in the supply of a tumor, it is essential to pay careful attention to the relative sizes of the branches of the middle meningeal artery, in particular. It should be determined if possible, whether small branches enter the tumor area from an apparently enlarged artery.

Several routine steps may be helpful to determine whether a branch of the external carotid artery is or is not supplying a tumor. First, the size of the trunk of the middle meningeal artery should be scrutinized. If there is an increased blood flow through the middle meningeal trunk (which is necessary to supply a tumor) the artery usually becomes tortuous in its initial portion before it bifurcates. The presence of tortuosity per se is not necessarily an indication of an increased blood flow through this artery. Some patients have a tortuous initial portion of the middle meningeal artery without having a neoplasm, but, if the tortuous segment is longer than I or 2 cm, it is probably pathologic.Second, the relative sizes of the various branches of the middle meningeal artery should be noted since a branch involved in the supply of a tumor will fill slightly earlier and be larger than the other branches . Third, a branch to a meningioma may not appear to be enlarged at its origin from the middle meningeal trunk; if the artery is followed to its periphery, however, it will be noted that, instead of getting smaller, it actually becomes larger as it approaches the region of the neoplasm. It is observed chiefly in the external carotid circulation, and rarely in the internal carotid system.

Such a finding is an important sign of blood supply of a tumor and is believed to be due to a reversal of blood flow in the many arterioles which anastomose within the meninges and the bone. They may join a principal vessel feeding the tumor, proceeding either from an adjacent branch of the middle meningeal, from accessory meningeal branches, or from superficial temporal arteries involved in the blood supply of the bone.

• The sunburst appearance

By virtue of this reversal of flow, more blood is drawn into the final segment of the artery to increase the blood supply of the neoplasm. Finally, a careful search should be made for multiple branches arising from any vessel in question, especially near its termination. Such branches may be very inconspicuous, or they may be extremely prominent.

When external carotid angiography alone is performed, the abnormal vessels are easier to visualize than when there is superimposition of branches of the internal carotid artery. The term sunburst appearance has been applied to this very distinctive angiographic finding which is characteristic of meningiomas but also seen in certain other vascular neoplasms, such as hemangiopericytomas.It is believed that the sunburst appearance is due to a radial distribution of the small arterial branches which seem to spring from a central point which probably represents the original site from which the blood supply was drawn at the beginning of the growth of the tumor.

The majority of meningiomas that occur over the cranial vault are supplied by branches of the middle meningeal artery and, as explained above, sometimes by the superficial temporal artery. Some meningiomas situated in the frontal fossa may be supplied by meningeal branches which normally feed the bone in this region and which arise from or anastomose with branches of the ophthalmic artery. Since the circulation through the internal carotid artery is swifter than the external, eventually a significant proportion of (or most of) the tumor blood supply may be by way of the ophthalmic artery. This vessel then becomes enlarged. In such cases it is possible to demonstrate angiographically branches arising from the superior aspect of the ophthalmic artery and extending upward to the roof of the orbit. Falx meningiomas arising in the frontal region (back to the coronal suture) may receive their blood supply partly from the anterior meningeal (artery of the falx) branch of the ophthalmic artery. The anterior meningeal artery (arising from the anterior ethmoidal branch of the ophthalmic) may become enlarged and can be followed along the inner table of the skull in the frontal region Although frontal midline meningiomas and subfrontal (olfactory groove) meningiomas usually derive their blood supply from the ophthalmic artery, tuberculum sellae meningiomas often do not have a principal ophthalmic supply.

Some tentorial meningiomas present another example of blood supply through the internal carotid artery, by way of its meningeal anastomotic branches. The tumor also receives branches from the external carotid system.

Meningiomas in the posterior fossa also may be supplied by accessory meningeal arteries. These are branches of the external carotid system entering the skull by way of the condyloid foramen and through the foramen lacerum. Anterior and posterior meningeal branches of the vertebral arteries also supply such lesions.

Branches of the middle meningeal and superficial temporal arteries sometimes overlie the area of a neoplasm, but this does not necessarily mean that they are supplying the lesion . The rules explained above, especially progressive vascular enlargement (paradoxical enlargement), should be followed in trying to evaluate the significance of vessels in, or about, a tumor area.

An occasional branch of the external carotid artery, most often the superficial temporal artery, may appear to enlarge on the late films of serialogram. It is necessary, however, to differentiate between actual enlargement of a vascular segment and its apparent enlargement which may be caused by laminar flow. The main stream of contrast substance is through the center of the artery, and the periphery of the vessel becomes opacified after the center. The later of two films may therefore show an arterial diameter which appears to be larger than on the earlier film. In addition, some enlargement may be a true vasodilatation due to the effect of the contrast material on the vessel wall. The angiogram usually serves to differentiate such an appearance from true enlargement.

• The vascular rim

Not all meningiomas are supplied principally by the external carotid artery and its branches. A significant number are supplied by both the external and the internal carotid arteries .In this case the periphery of the meningioma is supplied by branches from the internal carotid system that encircle the tumour and form the characteristic vascular rim,while the center of the tumour is supplied by branches from the external carotid system that radiated peripherally forming the sunburst appearance,and a small percentage draw exclusively from intracranial branches of the internal carotid artery. An example of exclusive internal carotid supply is the intraventricular meningioma, a tumor which is usually fed by the choroidal arteries.

• The venous blush

Although the vessel or vessels that actually supply a meningioma can usually be seen in the angiogram, sometimes they cannot, and only a large area of abnormal density can be discerned. The intrinsic vascularity of a tumor has previously been referred to as the “tumor cloud,” “stain,” or “capillary blush.” A homogeneous tumor cloud in which there is a fairly even distribution of the contrast material throughout the tumor is characteristic of meningiomas. In addition, persistence of the tumor cloud for a considerable period of time throughout the serialogram is of great importance in the diagnosis of meningiomas.

The stain may still be visible even on the last film taken 8 or 9 sec after the beginning of the injection.

Meningiomas usually exhibit a homogeneous cloud, but it must be appreciated that the stain can develop piecemeal; i.e., only a portion of the tumor may be opacified by one injection. It is not uncommon for one segment of the lesion to be supplied by the ipsilateral external carotid artery and for the remainder of the tumor to draw from the internal carotid artery, or fill via a branch of the contralateral external carotid system. Three (or more) parts of the tumor may fill from different systems. The better the tumor vessels are demonstrated by multiple selective arterial injections, the more fragmented the capillary blush. Therefore, it is necessary to visualize all possible afferent arteries of a meningioma, and mentally combine the stains, to gain a true concept of the size and location of the total tumor cloud. The supply to the hilus of a meningioma is virtually always from the external carotid system.

The intrinsic vascular outline of meningiomas is most often sharply circumscribed and lobulated in configuration. This characteristic is in contradistinction to some gliomas (usually mixed oligodendrogliomas and astrocytomas), which may present a homogeneous cloud but are not sharply circumscribed.

Meningiomas usually fail to exhibit prominent draining veins. With some meningiomas, thin veins may be seen at the periphery of the tumor. Some cases of angioblastic meningiomas may present numerous large veins with an increase in the speed of circulation through the tumor that produces early venous filling, similar to that seen with malignant tumors. Such lesions, however, that display draining veins, may exhibit all of the other characteristics of meningiomas. In these cases, the draining vessels are usually superficial cerebral veins. Deep veins may sometimes drain into the vein of Galen. Such veins indicate that there is invasion of brain tissue by the meningioma or, at least, that “tumor” vessels have appeared which bridge the space to the surface of the brain. Intraventricular tumors, of necessity, must drain by way of the tributaries of the thalamostriate and internal cerebral veins.

In trying to evaluate the importance of the above described characteristics of the abnormal circulation of meningiomas, the most significant features are considered to be:(I) a blood supply from the external carotid system, (2) a homogeneous but sharply circumscribed cloud, and (3) the persistence of the contrast substance within the tumor. In some cases, no blood supply can be traced from the external carotid artery into the meningioma, and a diagnosis must be based on other observations. Of the latter two findings, persistence of the tumor cloud appears to be slightly more reliable than homogeneity alone.

Because of pressure on superficial cerebral veins, slowing of the circulation through the area of a meningioma may be seen in the absence of abnormal vascularity. The surface veins in the tumor area fill later than normal, owing to local slowing of the circulation. The finding is nonspecific and may be found in cases of intracerebral tumors, as well .

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 7, 2009 — The radiologic investigation of the optic pathways plays an integral part in the diagnostic evaluation of diverse lesions, such as inflammatory disease, vascular disorders, and benign and malignant tumors that afflict the optic pathways. These radiologic methods consist principally of computed tomography (CT) and magnetic resonance (MR) imaging and, in vascular lesions, MR angiography and conventional angiography.

The radiologic indications are based on the neuro-ophthalmologic evaluation. The neuro-ophthalmologist, after a careful history and evaluation of visual function, visual fields, and papillary abnormalities, and optic kinetic findings, frequently can determine the suspected location of lesions in the anterior visual pathways or posterior visual radiations. Inspection of the eye, including adnexal structures and fundoscopy, provides further information in the clinical assessment of these patients. On the basis of these neuro-ophthalmologic findings, the appropriate study can be selected, and the radiologist can be alerted to investigate a particular area in the optic pathway. Due to technical advances in CT and MR imaging, the sensitivity in detecting lesions and determining the location and extent of a lesion has been advanced to a level with a high diagnostic yield .

The optic nerve is usually identified as a cylindrical structure, the total length of which measures approximately 4.5 cm, with an intraorbital component of approximately 25 to 30 mm. The width of the nerve should be approximately 4.5 mm as seen in the transaxial plane, but may actually measure approximately 5 mm when seen in the coronal plane. This is owing to the fact that the nerve is imaged obliquely in coronal scans.

OPTIC NERVE GLIOMA

Optic nerve gliomas are uncommon neoplasms. They represent approximately 4% of all orbital tumors, 2% of all intracranial tumors, and 4% of gliomas.Optic nerve gliomas outnumber meningiomas 3 or 4 to 1. The peak incidence is from 2 to 8 years of age with 75% manifesting in the first decade and 90% in the first two decades of life. There is a slight female preponderance. A common initial symptom is proptosis associated with decreased visual acuity. Other presenting symptoms may be nystagmus or strabismus.

Optic nerve lesions cause central or paracentral field defects, dyschromatopsia, and afferent pupillary defect .The afferent pupillary defect is a predominant finding in optic nerve lesions and occurs less commonly in lesions of the chiasm. It also can occur in optic tract lesions but much less frequently. Lesions in the optic nerve commonly are associated with disc edema, which can be seen on fundoscopy. If the edema persists, atrophy may ensue in approximately 6 to 8 weeks.

Optic nerve gliomas grow slowly but may grow in spurts. They may, however, be dormant without revealing any significant increase in size over many years. Spontaneous regression of an optic nerve glioma in patients with neurofibromatosis has been reported. Because of this erratic growth behavior, follow-up over many years is necessary. There is a high association of up to 50% with neurofibromatosis type CNF-1.

On pathologic examinations, some tumors resemble juvenile pilocytic astrocytomas. They grow slowly and almost always are only locally invasive with no tendency to malignant transformation. In their growth, they cause fusiform enlargement of the optic nerve, which is completely invested by the dura. If they extend through the optic foramen, they may have a dumbbell shape. On cut section, they are firm in consistency, but frequently have soft areas of myxomatous consistency. Cystic degeneration within the tumor has been described.The tumor usually blends gradually into the adjacent optic nerve. Hemorrhage with hematoma formation and necrosis are uncommon in optic nerve gliomas .

The normal histologic architecture of the optic nerve is usually completely effaced secondary to tumor growth into the nerve. The dura surrounding the tumor may remain intact. Invasion of tumor into the leptomeninges and growth within the subarachnoid space of the optic nerve is another feature of some of these tumors. The tumor may spread within the subarachnoid space beyond the area of origin in the nerve. This may be associated with a marked reactive fibroblastic proliferation within the subarachnoid space.

In approximately 50% of cases, arachnoid capsule hyperplasia is encountered.The capsule hyperplasia may extend beyond the limits of the intraneural portion of the glioma and, in some instances, for a considerable distance. Optic nerve glioma in the anterior visual pathway may be limited to the orbital optic nerve or extend into the intracranial cavity.Extension of optic nerve glioma to the globe with intraocular seeding has been described.

Prior to the introduction of CT and MR, conventional radiologic studies consisting of optic foramen views were obtained. These studies showed concentric enlargement of the optic canal in more than 50% of cases. The cortical margin usually is well corticated with no evidence of irregularity or sclerosis. It was, however, shown that not all optic nerve gliomas that extend through the canal cause enlargement of the foramen on radiologic studies. For refinement of the conventional film studies, polytomography was introduced, especially to show the chiasmatic sulcus, tuberculum sellae, and planum sphenoidale.

Intracranial tumor extension into the chiasm may be reflected by a J-shaped depression of the chiasmatic sulcus. Encroachment on the anterior clinoid process causes remodeling with pointing of the anterior clinoid processes.

On computed tomography (CT), intraorbital optic nerve gliomas are characterized by fusiform or sausage-shaped enlargement of the optic nerve. In a small percentage of cases, there may be marked fusiform to globular enlargement of the optic nerve with almost complete obliteration of the intraconal orbital fat. The margins are usually smooth, and there is a sharp interface with the surrounding orbital fat. Optic nerve gliomas are isodense with brain and show slight to moderate enhancement following the introduction of contrast material.

In cases with marked enlargement of the nerve, kinking and tortuosity can be noted . CT, however, does not allow the separation of the individual layers and CSF space of the optic nerve sheath complex.

On basal CT sections with bone window setting, there may be enlargement and funneling of the optic canal. In cases in which angiography is carried out, no hypervascularity of these gliomas is present. On CT, these tumors are isodense or hypodense with brain and show enhancement of a variable degree after intravenous contrast injection. Calcifications within these tumors are rare but may occur following radiation therapy. Rarely, tumor may extend into the sphenoid sinus.

• MR imaging of optic nerve glioma

The optimal assessment of optic nerve glioma is carried out with MR imaging. There is enlargement of the optic nerve sheath complex with a configuration that may be tubular, fusiform, eccentric, and globular with kinking and tortuosity . On Tl-weighted images, hypointensity of the tumor is present, whereas on the T2-weighted images, there is often increased signal intensity of the lesion .

Some heterogeneity of the signal intensities may be present on these T2- weighted images with a central area of low intensity that is occasionally surrounded by a zone of increased signal intensity .

Figure 3. MRI T1 precontrast studies showing two cases with optic nerve gliomas

The peripheral hyperintense portion on the long TR-TE sequences represents arachnoid hyperplasia or tumor intermixed with arachnoid. The arachnoid hyperplastic tissue reveals no enhancement . The enhancement of optic nerve glioma is variable from slight to marked enhancement . Peripheral enhancement of optic nerve gliomas and chiasmatic gliomas may represent extraneural growth of tumor within the subarachnoid space with the normal nerve structure reflected by the low intensity normal nerve.

Extension of optic nerve gliomas to the chiasm via the optic canal produces a dumbbell shaped configuration. Optic nerve gliomas may be associated with dilatation of the cerebral spinal fluid in the subarachnoid space . This may be secondary to obstruction in the outflow of cerebral spinal fluid or trapping of fluid by the arachnoid hyperplasia.

Gliomas of the anterior visual pathway may be limited to one or both optic nerves or may extend posteriorly into the chiasm and, in advanced cases, to the chiasm and the optic tracts unilaterally or bilaterally. When extension into the optic canal and intracranial cavity occurs, there is enlargement of the optic canal, which is encountered in more than 50% of cases. Extension to the chiasm with formation of a bulky mass may lead to enlargement and depression of the chiasmal sulcus, flattening of the tuberculum sellae, undercutting of the anterior clinoid processes, and thinning of the optic strut.

Extension of gliomas into the posterior optic pathway, especially chiasm and optic tracts, may form a large mass growing into the adjacent brain . Associated enlargement of the Sylvian suprasellar and prepontine cisterns may be present reflected by low density areas surrounding the tumor mass. Large tumors in the suprasellar area may simulate other suprasellar tumors, but involvement of the intraorbital optic nerves can be helpful in the differential diagnosis of these suprasellar masses.

• Optic Nerve Glioma and Neurofibromatosis.

Optic nerve glioma may occur in conjunction with neurofibromatosis, and the incidence has been reported in 10% to 15% of cases. As in patients without neurofibromatosis, the growth rate is variable, but involvement of both optic nerves is more common . These gliomas may extend posteriorly with involvement of the chiasm, optic tracts, and adjacent anatomic areas.

A frequent finding is the association of hamartomatous lesions of the brain in patients with neurofibromatosis type I. They display increased signal intensity on T2-weighted images, sporadically on TI-weighted images and a variable degree of enhancement. A decrease in size, signal intensity, and enhancement has been reported over time.

The hamartomatous lesions are composed of dysplastic glial tissue in the white matter of the various parts of the brain such as the basal ganglia, internal capsule, temporal and parietal lobes, mid brain, pons, and cerebellum. These hamartomatous areas are reflected by increased signal intensity on the long T2- weighted images, including proton density images. They exhibit no mass effect or edema and fail to enhance with gadolinium. Rarely, a change in size (either an increase or decrease) has been reported. The heterogeneity and spectrum of these tumors and hamartomatous lesions is further exemplified by their presence on MR imaging studies performed for a routine work-up or for evaluation of nonophthalmologic symptoms in patients with neurofibromatosis type I (NFl). Other central nervous system tumors, including astrocytomas, ependymomas, and meningiomas, are encountered with greater frequency in patients with NFl.

• Malignant Optic Nerve Glioma.

Malignant optic nerve glioma is a rare optic pathway tumor that is distinct from the benign glioma of childhood.It is more prevalent in males, and the peak incidence is between 40 and 50 years of age. The presenting symptoms include rapid loss of vision (frequently bilateral) associated with dyschromatopsia, field defects, optic disc edema or atrophy, afferent pupillary defect, and orbital pain. The tumor involves predominantly the intracranial optic nerves and chiasm with secondary extension to the hypothalamus, optic tracts, and third ventricle. Tumor location limited to the intraorbital optic nerve is less common.Histologic examination of biopsy and necropsy material reveals anaplastic astrocytoma or glioblastoma multiforme. The overall mortality rate of this disease approaches 100%, with a mean survival of 9 months following initial diagnosis. Treatment by radiation therapy and chemotherapy thus far has not significantly altered the fatal outcome.

The preferred imaging modality is MR imaging with gadolinium, because, in the early stages of the disease, only slight enlargement of the anterior optic pathway may be visible only when gadolinium enhancement occurs. At this early stage, the tumor simulates an early inflammatory process including optic neuritis and sarcoid.

Before MR, the early diagnosis was often made by surgical intervention with a biopsy. Further tumor growth leads to enlargement of the optic nerves, chiasma and involvement of the optic tracts, hypothalamus, and third ventricle. Enhancement occurs postintroduction of gadolinium.

OPTIC SHEATH MENINGIOMA

Optic nerve sheath meningiomas represent fewer than I % of all meningiomas. They constitute approximately 3% to 5% of orbital tumors. They occur predominantly between the ages of 30 and 50 years but may occur at any age, including childhood. Primary intraorbital meningiomas in children are more aggressive than similar tumors in adults. There is a 3 to 1 female predominance.

The most frequent symptoms consist of progressive loss of vision with proptosis, disc edema, or pallor. Papilledema is present in the early stages and eventually proceeds to atrophy, reflected by a white, sharply delimited disc on fundoscopy.

Ophthalmologic examination demonstrates central scotomas with generalized constriction of the visual field or overall depression of the visual field. These findings become progressively worse and eventually the patient may become blind over time.

Optocililiary shunt vessels are occasionally demonstrated in the papillary area on fundoscopy. Optic nerve sheath meningiomas occur along the intraorbital portion of the optic nerve approximately three times more frequently than in the canal. Bilateral optic nerve sheath meningiomas are uncommon. The histologic types are not different from meningiomas encountered in the intracranial cavity.

On CT, optic nerve sheath meningiomas originate in the capsules of the arachnoid. They grow along the nerve but may penetrate the dura and expand into the adjacent orbital fat. Growth may be circumferential along the optic nerve sheath imparting a tubular configuration to the enlarged optic nerve. They may, however, grow eccentrically from the optic nerve sheath and cause asymmetrical enlargement of the entire or part of the optic nerve sheath . The optic nerve usually is embedded in the tumor .

If eccentric growth prevails, the optic nerve may be located at the margin of the tumor with concommitant displacement away from the tumor, often medially. In these circumstances, the optic nerve sheath meningioma may simulate a tumor within the orbit that has encroached on the optic nerve.

Figure 6. Precontrast CT study showing a heavily calcified concentric optic sheath meningioma

Significant globular extrinsic growth is not infrequently encountered in the optic nerve near the globe. The dura is thinned, because of spreading out into the adjacent sclera. Optic nerve sheath meningiomas, in rare instances, may grow into the optic disc of the eye and adjacent choroid .

Figure 7. Precontrast CT study showing heavily calcified concentric optic sheath meningiomas

Meningiomas tend to be hyperdense on the CT study and not infrequently reveal globular, linear or plaque-like calcifications . Contrast enhancement in optic nerve sheath meningioma is often intense surrounding the nonenhancing optic nerve. On the CT study, a lucent area is noted throughout the dense enhancing tumor referred to as a “railroad track sign” . This feature is noted on axial and coronal images.

Optic nerve sheath meningiomas may extend from the orbital part of the sheath into the optic canal and cause enlargement and occasionally hyperostosis of the margin of the canal.

• MRI imaging of optic sheath meningioma

On MR imaging, optic nerve sheath meningiomas reveal low signal intensity on the Tl-weighted and T2-weighted images. MR frequently fails to demonstrate small areas of calcification within the optic nerve sheath. Larger amounts of calcium are reflected by low signal intensity on the TI-weighted and T2-weighted images. There is frequently marked enhancement of the meningioma, similar to meningiomas in the intracranial cavity.

Figure 10. MRI T1 precontrast studies of two cases with bilateral concentric hypointense optic sheath meningiomas

Extension into the optic canal and adjacent intracranial cavity is demonstrated optimally with MR imaging and gadolinium . These intracranial extensions reveal marked enhancement and are ideally defined in their location and extent. Fat suppression technique always should be used to contrast the enhancing tumor with the darkened fatty tissue.

Figure 12.  MRI T1 precontrast studies showing concentric [left] and eccentric [right] hypointense optic sheath meningiomas

Meningiomas that arise within the intracranial cavity, particularly from the tuberculum sellae, anterior clinoid processes, and lesser wing of sphenoid may secondarily invade the optic nerve sheath in the optic canal and may further proceed into the orbital apex.These lesions are well delineated on MR with gadolinium using different projections, such as axial, coronal, and parasagittal. Clinically, they cause marked compromise in vision and frequently reveal no proptosis

Figure 13. MRI T1 precontrast studies showing concentric [left] and eccentric [right] hypointense optic sheath meningiomas

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.3a July 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 6, 2009 — Tuberous sclerosis is a hereditable disorder characterized by the development of early in childhood of hamartomas,malformations and congenital tumours of the CNS, skin and viscera. The pathological changes of tuberous sclerosis are widespread and include lesions in the brain,skin,bone,retina,skin and others. Clinically it is characterized by the occurrence of epilepsy, mental retardation and adenoma sebacious in various combination.

The brain is usually normal in size,but several or many hard nodules occur on the surface of the cortex or along the subependymal covering of the ventricular system. These nodules are smooth, rounded or polygonal and project slightly above the surface of the neighboring cortex. They are whitish in color and firm.

Figure 1. Precontrast CT scan showing periventricular tubers,noncalcified [left] and calcified [right]

These nodules are variable in size and might attain a huge size.On sectioning the brain ,sclerotic nodules may be found in the subcortical gray matter,the white matter and the basal ganglia.The lining of the lateral ventricles is frequently the site of numerous small nodules that project into the ventricular cavity (candle guttering). Sclerotic nodules are characteristically found in or near the foramen of monro and commonly induce hydrocephalus. The cerebellum,brain stem,and spinal cord are less frequently involved

Histopathologically,the nodules are characterized by the presence of a cluster of atypical glial cells in the center and giant cells in the periphery .The nodules are frequently ,but not necessarily,calcified.These nodules are occasionally called giant cell glioma when they are large in size.

Other pathological features include heterotopia,vascular hyperplasia or actual angiomatous malformation

NEUROFIBROMATOSIS

Neurofibromatosis is a hereditary disorder characterized by the occurrence of a variety of intracranial and spinal neoplasm which include acoustic neuromas, meningiomas,gliomas(mainly optic nerve gliomas). These tumours may occur in various combinations in the same patient. Neurofibromatosis exist in two clinical forms

• Type I neurofibromatosis

• Type II neurofibromatosis [bilateral acoustic neurofibromatosis]

Characterized by the existence of bilateral acoustic neurofibromas and a multiplicity of other central intracranial or spinal neoplasms [meningiomas,gliomas,or neurofibromas] .peripheral lesions are quite uncommon in type II neurofibromatosis and cafe-au-lait patches are rare in this type.

ENCEPHALOTRIGEMINAL ANGIOMATOSIS (STURGE WEBER SYNDROME)

Encephalotrigemenial angiomatosis classically includes the presence of cutaneous vascular portwine nevus of the face, contralateral hemiparesis or hemiatrophy, glucoma,seizures and mental retardation

• Pathology

The occipital lobes are affected most often,but lesions may affect the temporal or parietal lobes. Atrophy is characteristically unilateral and ipsilateral to the facial nevus. Leptomeningeal angiomatosis with small venules filling the subarachnoid spaces is a common finding.Calcifications of the arteries on the surface of the brain is very common and frequently extend to involve the intracerebral microvascular system. The trolley-track or curvilinear calcifications seen on skull x ray is due to calcification of the outer cortex or vascular calcification.

Figure 5. Plan x ray showing two cases with Sturge- Weber syndrome, notice the trolley-track or curvilinear calcifications.

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.2a April 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 6, 2009 —  Orbital pseudotumour is a ideopathic non specific inflammatory process affecting the intraorbital structures with a tendency for chronicity,one of the following structures ,or a combination of the following structures,are involved in the nonspecific inflammatory process

Pseudotumor is divided into acute, subacute, and chronic forms. These subcategories are based on the degree of inflammatory and fibrovascular response.

• Acute stage

In the acute form of the disease, there is a polymorphous infiltrate composed of mature lymphocytes, plasma cells, macrophages, eosinophils, and polymorphonuclear lymphocytes. Multinucleated foreign body giant cells secondary to fibrosis also have been described but are rare. The cellular infiltrate or orbital pseudotumor tends to be diffuse and multifocal. Occasionally vasculitis, affecting small arteries of the orbit, may be associated with idiopathic orbital pseudotumor .

• Subacute stage

In the subacute and chronic idiopathic orbital pseudotumor, there is formation of increasing amounts of fibrovascular stroma affecting muscles, fat, and glandular elements. This fibrotic response may eventually result in dense fibrosis with fixation of orbital structures. Lymphoid follicles with germinal centers may be interspersed, especially in the chronic phase.

The acute inflammatory process may lead gradually into the fibrotic stage; however, some cases of nonspecific idiopathic orbital inflammation are primarily sclerotic in nature and may present and progress insidiously without passing through a prior acute inflammatory phase.

The lacrimal gland is the most frequent orbital structure involved in pseudotumor. There is usually diffuse enlargement of the lacrimal gland with preservation of the shape of the gland .The most marked expansion occurs in the anteroposterior diameter along the lateral orbital wall and lateral rectus muscle. There may be an associated inflammatory reaction in the periglandular tissue imparting poor definition to the margins of the gland. There is usually pain and tenderness on palpation and some inflammation of the adjacent globe. There are no specific density characteristics on CT or MR images to differentiate glandular enlargement from other causes (bacterial inflammation sarcoid, or lymphoproliferative disease).Prompt response to steroid treatment, in conjunction with the radiologic findings, support the diagnosis of pseudotumor. A biopsy is indicated in cases where such response is lacking.

Occasionally, a pseudotumor forms an orbital mass that, however, is most often ill- defined and heterogeneous in composition . Some of these pseudotumor masses may invade the extraorbital structures ,including intracranial cavity. Pseudotumor infiltrations may extend along the optic nerve sheath from the globe to the optic canal causing diffuse enlargement of the optic nerve sheath complex.

On contrast CT, there is enhancement of the sheath contrasting against the central low density nerve .Orbital apex pseudotumor may compress, obliterate, or displace the optic nerve . The optic nerve sheath is characterized by a lucent band representing cerebrospinal fluid (CSF) in the subarachnoid space. A subcategory of diffuse orbital inflammatory pseudotumor is sclerosing pseudotumor . This process may represent the endstage of a subacute pseudotumor or may arise in the orbit de novo. There is a diffuse increase in density of the orbital fat with obliteration of the optic nerve, muscles, and circumferential involvement of the globe

• Chronic stage

There is complete fixation of the intraorbital structures with no motion of the globe. If the inflammatory process in the orbital apex extends to the cavernous sinus, the Tolosa-Hunt syndrome is evoked. In these cases, there is enlargement of the cavernous sinus on the involved side. On CT and MR imaging, there is diffuse enhancement following administration of contrast material . Associated with these findings may be narrowing of the intracavernous carotid artery. The Tolosa-Hunt syndrome is characterized clinically by the onset of ophthalmoplegia. Following administration of steroids, symptoms abate and there is resolution of the cavernous inflammation.

Involvement of the globe is not an uncommon finding in pseudotumor. On the CT and MR imaging studies, there is diffuse enlargement of the sclero-uveal coat, which cannot be separated into the individual layers such as retina, choroid, or sclera.The inflammatory process is usually located in Tenon’s space, a potential space between Tenon’s capsule and the sclera. There is usually enhancement of the sclera following contrast administration. There may be an associated inflammatory reaction in the uvea,which is composed of choroid, ciliary body, and iris. Not infrequently, there is an associated inflammatory infiltrate in the adjacent anterior orbital fat around the globe.

• Differential diagnosis of pseudotumour of the orbit

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.2a April 2009 [Click to have a look at the home page]

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

July 6, 2009 — Chordoma arises from the residual remnants of the embryonic notochord. The skull base is involved in one third of cases; chordoma represents 1% of all intracranial tumors and 3% to 4% of all primary bone tumors. The clivus near the spheno-occipital synchondrosis is primarily involved; however, rare primary chondroma sites have been reported in the nasopharynx, nasal cavity, and maxillary antrum. The common clinical features are primarily due to progressive cranial nerve involvement.

• Imaging Findings

On noncontrast CT scans, extensive bony destructive changes involving the clivus and adjacent bones can be seen. Tumoral calcification is common. On MR imaging scans, tumor appears as low signal in TI-weighted images, and T2-weighted images show heterogeneous increased signal with areas of signal void from calcifications and chips of eroded bone. Heterogeneous enhancement of the tumor is seen after contrast administration . The tumor is usually avascular, but a tumor stain may be visualized through angiography

Figure 1. CT scan showing clivus chordoma

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) WEB-CD agency for electronic publication, version 10.2a April 2009 [Click to have a look at the home page]