Spinal tumors

The author: Professor Yasser Metwally

http://yassermetwally.com

INTRODUCTION

Imaging of tumors in the spine has changed dramatically over a relatively short period of time. With magnetic resonance (MR) imaging as the primary imaging modality, there has been a quantum leap in terms of quality of information gathered and patient comfort. Tumors of the spine are easily classified as extradural, intradural/extramedullary, and intramedullary. Regarding spinal tumors in general, extradural lesions occur most commonly and most are metastatic. Of the intradural lesions (which are rare), 84% are extramedullary, the majority being nerve sheath tumors or meningiomas. Approximately 16% of intradural tumors are intramedullary, the most common being ependymoma followed by astrocytoma.

EXTRADURAL, PRIMARY BONY NEOPLASMS

  • Metastatic Disease

The majority of metastatic lesions in the spine arise from hematogenous spread to vertebral bodies and appear hypointense relative to normal marrow on Tl-weighted MR images and hyperintense on T2-weighted images. In some cases, the lesion(s) may be evident only on Tl- or T2-weighted images . Sclerotic bone metastases may appear hypointense on both Tl- and T2-weighted images. Disruption of cortical bone and associated soft tissue mass are important ancillary findings. Disc spaces are preserved, in contradistinction to infectious processes.

  • Multiple Myeloma

The spine is the most common site of involvement with multiple myeloma. Extradural compressive lesions are a well known complication of this disease. The lesions appear hypointense on TI-weighted images and homogeneously hyperintense on T2- weighted images. Lesions are best depicted on T2-weighted or fat suppressed images. There may be a decrease in T2-weighted signal intensity with treatment. As with metastatic lesions, contrast enhancement is generally not useful, except in following response to treatment.

Figure 1. MRI T1, precontrast showing solitary myeloma involving the second cervical vertebra,notice the T1 hypointensity. (Click to magnify figure)

  • Lymphoma

Spinal involvement is not uncommon with lymphoma. This can arise secondarily from extension of disease involving paravertebral lymph nodes into the vertebral body or through foramina into the epidural space. The tumor may also primarily infiltrate the vertebral body or epidural space. Epidural extension of tumor directly from a vertebral body is common. The multiplanar ability and high resolution of MR imaging are ideally suited to demonstrating all of these possible growth patterns. The soft tissue mass appears iso- to hypointense relative to muscle on TI -weighted images. Vertebral lesions appear hypointense relative to bone marrow on TI-weighted images. On T2-weighted images, these may appear inhomogeneously iso- to hyperintense, because of uneven infiltration of the marrow. Rarely, patients with acute myelogenous leukemia may develop spinal cord compression secondary to a solid mass of myelogenous stem cells (chloroma, granulocytic sarcoma), which appears isointense with spinal cord on TI-weighted images and hyperintense on T2- weighted images .

  • Other Primary Bone Tumors

Primary malignancies of bone represent only I% of all cancers; of these, approximately 10% involve the axial skeleton. Tumors are generally classified according to their tissue of origin (cartilaginous, osteoid, fibrous, vascular, and marrow elements), each giving rise to both benign and malignant lesions. Paraspinal lesions may involve both soft tissue and bone, and the cell of origin may not be clear . The most common benign primary tumor is giant cell tumor, followed by osteoid osteoma and osteoblastoma.

INTRADURAL EXTRAMEDULLARY TUMORS OF THE SPINE

  • Nerve Root, Nerve Sheath Tumors

Schwannomas are encapsulated, solitary tumors that derive from Schwann cells . They arise adjacent to, and displace the involved nerve root. Multiple schwannomas occur in neurofibromatosis type 2 (NF2). Neurofibromas are composed of perineural and Schwann cells, fibroblasts, and a mucopolysaccharide matrix; they engulf the involved nerve root. They are usually multiple and associated with NF2 .

Figure 2. MRI T1 ,precontrast [left, middle] and postcontrast [right] showing a spinal schwannoma, notice the T1 hypointensity and the dense contrast enhancement (Click to magnify figure)

Schwannomas and neurofibromas typically involve the dorsal sensory nerve roots. Depending upon their site of origin, they can be intradural, extradural, or both, forming a “dumbbell” or hour-glass shaped mass. Rarely, schwannomas may extend into the substance of the spinal cord and be entirely intramedullary in location. Plain radiographs may show an enlarged neural foramen or spinal canal. There may be associated findings of neurofibromatosis (scoliosis, vertebral dysplasia). CT-myelography will show the bony changes if present and an intradural, extramedullary mass with rounded, well-defined margins. Schwannomas appear iso- to hypointense relative to spinal cord on TI-weighted images and hyperintense on T2-weighted images. Areas of even greater signal hyperintensity on T2-weighted images may represent cyst formation; conversely, areas of relatively decreased signal intensity on T2-weighted images may relate to intratumoral hemorrhage, dense cellularity, or collagen deposition. The tendency for cyst formation is greater in spinal tumors than in intracranial lesions.

Figure 3. Neurofibroma is a solid tumor; cystic areas are uncommon (Click to magnify figure)

In contrast, neurofibroma is a solid tumor; cystic areas are uncommon. They have more uniform signal intensity on MR images, in keeping with their more uniform histologic appearance on the T2-weighted images, a target appearance may be seen with relatively greater signal intensity peripherally, corresponding to peripheral myxomatous tissue and central fibrocollagenous tissue seen histologically. Contrast- enhanced MR imaging may show a central area of decreased signal intensity surrounded by enhancing tumor in either neurofibroma or schwannoma.

Figure 4. MRI T2 images showing a dumb-bell neurofibroma notice the T2 hypointensity [middle image] which could be due to intralesional haemorrhage (Click to magnify figure)

These tumors show variable hyperintensity in T2-weighted images;the target sign is occasionally demonstrated (a peripheral hyperintense rim and a central low intensity) in T2-weighted sequences This target pattern is attributed to peripheral myxomatous tissue and central fibrocollagenous tissue. This pattern is absent in lesions with cystic, hemorrhagic, or necrotic degeneration.

Figure 5. MRI T2 images showing the target sign,with central hypointensity corresponding to the fibrocollagenous core and a peripheral hyperintensity corresponding to the peripheral myxomatous tissue (Click to magnify figure)

Plexiform neurofibroma is a distinct lesion that is characteristic of NFl. Although these are infiltrative lesions that occur most commonly near the orbital apex or superior orbital fissure, they can occur anywhere in the body. On MR imaging, the lesions appear hypointense relative to cord on TI-weighted images and hyperintense on T2-weighted images with variable contrast enhancement.

  •   Spinal meningioma

Spinal meningiomas predominate after the fourth decade and show a striking female predominance. The thoracic region is involved most frequently, followed by the cervical spine. Most meningiomas are globoid in shape although a few assume an “en plaque” configuration. Most are confined to the intradural space, although some may extend through the nerve root sleeve into the paraspinal region. They arise from meningothelial cells that are clustered around the spinal nerve roots.

Figure 6. MRI T1 images (A, precontrast and B, postcontrast) and T2 image (c) showing a high cervical syncytial meningioma, notice the precontrast T1 slight hypointensity, the dense contrast enhancement, the cavity caudal to the tumour (A) and the T2 hyperintensity (C). Also notice the CSF cleft that separate the tumour from the spinal cord (A) (Click to magnify figure)

Similar to intracranial lesions, spinal meningiomas tend to be isointense to spinal cord on TI-weighted images and show relatively low signal intensity on T2-weighted images, relative to the surrounding hyperintense CSF . As with intracranial lesions, intraspinal meningiomas show intense enhancement, tend to have a broad dural attachment, and may demonstrate an enhancing dural tail.

Figure 7. MRI T1 images precontrast (A) and postcontrast (B,C) showing a dorsal syncytial meningioma, notice the T1 hypointensity (A), the dense contrast enhancement and the dural tail (B,C) (Click to magnify figure)

INTRAMEDULLARY TUMORS

  • Ependymoma & Astrocytoma

Approximately 63% of spinal intramedullary gliomas are ependymomas. Excluding ependymomas of the filum terminate, astrocytomas account for 47% of tumors and 40% are ependymomas . The majority of spinal cord astrocytomas are histologically low grade. It is important to attempt to distinguish an ependymoma from an astrocytoma preoperatively as the neurosurgeon will attempt complete extirpation of ependymoma, whereas the infiltrative astrocytoma will not be completely resectable.

Both types of lesion will generally show focal cord expansion, signal hypointensity on Tl- weighted images, and hyperintensity on T2- weighted images . Edema is frequently observed rostral and caudal to astrocytomas, and associated cavities are common; these features, however, are not useful predictors of histologic grade. Hypointensity (secondary to previous hemorrhage) at the tumor margin or within the tumor on Tl- and T2-weighted images suggests the diagnosis of ependymoma and the potential for complete resectability.

Figure 8. MRI T1 postcontrast images showing two cases of intramedullary astrocytomas, notice the dense enhancement and the associated cavitations (Click to magnify figure)

Figure 9 MRI T2, T1 images showing intramedullary cystic ependymoma extending from C4 to D4. Notice the transverse septations and the T2 hypointensity at the caudal end the center of the tumour (blood product) which is characteristic of ependymoma (Click to magnify figure)

The enhancement patterns of the lesions differ significantly with ependymoma showing focal enhancement involving the entire cross-section of the cord and astrocytoma showing more patchy, peripheral enhancement. All of the astrocytomas, even the low grade lesions, show some degree of enhancement. Contrast administration helps delineate tumor from edema and also helps to distinguish cystic areas within lesions. It can identify areas of tumor most suitable for biopsy. Volume of enhancing tumor is useful in following response to therapy.

Figure 10. MRI T1 precontrast [left], postcontrast [middle] and T2 image [right] showing a case of intramedullary ependymoma, notice the cystic breakdown,the faint enhancement (A,B), also notice the cord oedema and the patchy tumour T2 hypointensity that is due to intralesional haemorrhages (C) (Click to magnify figure)

  • Hemangioblastoma

Hemangioblastoma is the third most common spinal intramedullary neoplasm. Approximately one third of patients will have associated Von-Hippel Lindau disease. This tumor can usually be diagnosed preoperatively based upon MR and angiographic findings. MR imaging will reveal a focal enhancing mass, frequently accompanied by cysts or syrinx, or both. Flow-related signal void in one of the vessels supplying the lesion may also be noted.

  • Intramedullary Metastases

Metastases from non-central nervous system (CNS) primaries were previously found mainly at autopsy but, with the advent of MR imaging, are discovered antemortem with increasing frequency. Breast and lung carcinomas are the most frequent causes, followed by lymphoma, melanoma, and renal cell tumors. The lesions are usually solitary and extend over two to three spinal segments. Although the appearance of such lesions on MR scans is not specific, the patient history usually contributes to the correct diagnosis. Prognosis for patients with these lesions is very grave with survival being weeks to months despite radiation therapy.

  • Spinal Cord Lymphoma

Primary spinal cord lymphoma is rare. Spinal cord lymphoma can develop as part of a simultaneous multicentric CNS lymphoma, secondary to systemic lymphoma, or by local invasion of meningeal or epidural tumor.

REFERENCES

Metwally MYM, [1991] : Value of CT scan in the evaluation of spinal cord disorders. MD thesis, Ain shams university, Cairo, Egypt.

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