These lesions are found outside the dural sac involving the epidural space, paravertebral soft tissues, and spinal skeleton. The most common extradural masses are metastases from primary breast, lung, prostate, myeloma, and lymphoma. MRI is the preferred imaging modality to detect these lesions. Primary bone tumors rarely involve the lumbar spine. Nerve sheath tumors may present as extradural lesions but this is less common than their presentation in the intradural compartment. Chordomas classically occur in the sacrum and coccyx.
Metastatic disease frequently affects the spine primarily involving the vertebral body, usually followed by neoplastic infiltration of the posterior elements and epi-dural compartment (Fig. 16). The vast majority of these lesions arise from hematogenous spread to vertebral bodies. The usual MRI appearance is neoplastic replacement of the normal fatty marrow with hypointense T1 signal and hyperintense T2 signal relative to bone marrow. Well defined oval or round lesions are commonly seen but other patterns of neoplastic infiltration include diffuse replacement of the marrow, heterogeneous marrow replacement, and sclerotic bone metastases typically seen with prostate carcinoma. Sclerotic metastases demonstrate low signal on both T1 and T2W images. Metastatic disease usually shows contrast enhancement. In non-fat-suppressed T1W images, the lesions may become isointense with normal marrow after contrast making their identification difficult. There is better delineation of these lesions using fat saturation pulse sequences. Epidural and paravertebral
masses show inter- mediate T1 signal with contrast enhancement, which is accentuated if fat suppression techniques are applied.
Multiple myeloma commonly spreads to the spine and generally involves the vertebral body. Extradural compressive masses are frequent in the epidural space. A solitary spinal lesion may be the manifestation of the solitary form of multiple myeloma, plasmacytoma (Fig. 17). This occurs in younger individuals who eventually develop diffuse disease. The MRI findings of the disease also show decreased signal on T1WI and increased signal on T2WI. Enhancement is variable but usually present. Fat suppression is helpful in assessing the extent of neoplastic involvement.
Spinal involvement of lymphoma usually represents a secondary neoplasm. It may occur from direct extension of the disease from affected lymph nodes or secondary to hematogenous dissemination. Non-Hodgkin's lymphoma (NHL) is more common than Hodgkin's disease (HD). It commonly involves the vertebral marrow and the epidu-ral space. Features on MRI that may suggest the diagnosis include an epidural mass that is isointense relative to the cord on T1 and T2WI that demonstrates homogeneous
enhancement, and frequently extends to several vertebral levels. It may also show iso- to hyperintense signal relative to cord on T2WI. The tumor has a predilection for the thoracic spine followed by the lumbar spine. Diffuse vertebral marrow signal changes are commonly present.
There is marrow replacement by areas of low signal on T1WI, variable iso- to hyperintense signal on T2WI, and enhancement following gadolinium administration. In the pediatric population, leukemia has a similar appearance.
Hemangiomas are common incidental vertebral lesions. Some lesions may expand and become symptomatic. The most common sites are the thoracic and lumbar spine. The usual MRI appearance is a well-defined mass with hyperintensity on both T1 and T2WI (Fig. 18). The enhancement is variable. Hemangiomas with more vascular stroma demonstrate low signal on T1WI and high T2 signal, and must be distinguished from other primary and secondary vertebral tumors.
Primary bone tumors of the spine are rare and include giant cell tumors, aneurysmal bone cysts, osteoid osteo-mas, osteochondromas, and osteoblastomas (Fig. 19).
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