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     Nerve Sheath Tumors

      Nerve sheath tumors include both neurofibroma and neurilemoma (schwannoma). They originate from Schwann cells of the myelin sheath that invest the nerve roots as they exit the spinal column. Schwannomas are usually solitary lesions and do not incorporate the nerve root. Neurofibromas are associated with neurofibromatosis and are generally multiple, and the nerve fibers become entangled within the tumor, making resection difficult without sacrificing the nerve. Nerve sheath tumors can be intradural, extradural or both, giving them a dumbbell appearance.

      Bone erosion with scalloping of the vertebral body margins or widening of the neural foramen with erosion of the pedicles is the hallmark of the nerve sheath tumors. Even in the absence of bone erosion, extension of a soft-tissue mass through the neural foramen with a dumbbell configuration is quite characteristic. Endnote The signal characteristics of nerve sheath tumors are somewhat different from those of meningiomas. Nerve sheath tumors typically have a T1 that is slightly longer than or equal to that of the spinal cord. Lengthening of the TR and TE to increase T2-weighting results in brightening of the tumor. T2-weighted images, particularly with fat suppression, provide good contrast between the hyperintense schwannoma, medium intensity paravertebral muscles, and hypointense fat.

      Neurofibromas and schwannomas enhance brightly and uniformly with gadolinium. Enhancement is most helpful for intradural lesions, for detection of the smaller ones and definition of the larger ones. Gadolinium is less helpful for extradural lesions because the enhancing tumor becomes isointense to the surrounding fat. Fat suppression improves the contrast between enhancing extradural tumors and surrounding tissues. 

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