Tumors of the Cranial/Spinal Nerves

CHAPTER 37 Tumors of the Cranial/Spinal Nerves



Primary tumors of the cranial and spinal nerves derive from the cellular and extracellular support structures of the nervous system, rather than the functional neurons per se. The tumors are generally benign, slow growing, and often asymptomatic findings. Surgery is typically reserved for symptomatic cases and cases in which rare malignant transformation is suggested. Each of the tumors may arise sporadically or be part of the constellation of pathologic processes within specific genetic conditions.


Schwannomas account for 68% of intracranial neoplasms and 30% of primary spine tumors. Acoustic (vestibular) schwannomas are by far the most common among all intracranial nerve schwannomas. The incidences of nonvestibular schwannomas are as follows: cranial nerves (CNs) V > > IX > X > VII > XI > XII > III > IV > VI. CNs I and II do not exhibit schwannomas because they are not peripheral nerves but rather extensions of the central nervous system. Neurofibromas represent 5% of all benign soft tissue tumors.


In the United States, optic nerve gliomas represent 4% of orbital tumors, 4% of intracranial gliomas, and 2% of intracranial tumors. They also comprise two thirds of all primary optic nerve tumors.1 Aggressive optic gliomas are a rare, unusual presentation of the more common adult astrocytoma.2



SCHWANNOMA


Schwannomas are benign, rare tumors of Schwann cells that invest the nerve sheaths of intracranial and extracranial peripheral nerves. They are also referred to as neuromas, neurilemmomas, and nerve sheath tumors.




Clinical Presentation


The clinical presentation of cranial schwannomas is variable and depends on the specific segment of the intracranial or extracranial nerve involved.


Schwannomas involving the oculomotor, trochlear, and abducens nerves are rare (Fig. 37-1). Presenting symptoms can include palsy of the affected muscle and ipsilateral cavernous sinus symptoms if the mass is in the cavernous sinus.4,5









Jugular Foramen Schwannoma

The most common presentation of jugular foramen schwannomas (involving CNs IX > X > XI) is sensorineural hearing loss (90%). This presumably results from the superomedial vector spread of these tumors (Figs. 37-5 and 37-6). CN IX to XI neuropathy occurs late in the disease progression. This may include glossopharyngeal dysfunction (e.g., hoarseness, difficulty swallowing, aspiration) and/or spinal accessory symptoms (e.g., trapezius atrophy). Hoarseness also may occur with involvement of the recurrent laryngeal branch of CN X. Other presenting signs and symptoms may include dizziness with cerebellar compression and jugular vein occlusion.








Pathophysiology


The natural history of the majority of schwannomas is that of a slow-growing benign tumor. However, 10% of acoustic schwannomas demonstrate rapid growth (≥1 cm/yr). Malignant transformation is exceedingly rare.6 Schwannomas commonly present as sporadic tumors but may present as part of the constellation of multiple inherited schwannomas, meningiomas, and ependymomas (MISME) in the setting of NF2. Multiple peripheral schwannomas may rarely occur in the absence of other NF2 features, and this is referred to as schwannomatosis.


The vast majority of schwannomas occur as a result of sporadic mutations. Sixty percent of sporadic vestibular schwannomas specifically demonstrate inactivation of the NF2 tumor suppressor gene through point mutations, loss of the NF2 locus on chromosome 22q, or loss of chromosome 22 entirely.7,8 Carney complex is a rare autosomal dominant disease caused by mutation in the gene encoding the regulatory subunit of protein kinase A. The disease locus has been mapped to chromosome 17. Carney complex manifests as an array of pathologic processes, including melanotic schwannomas, cutaneous myxomas, potentially life-threatening cardiac myxomas, and pigmented adrenal tumors.9


Specific differential considerations should be made when evaluating schwannomas involving particular intracranial and extracranial peripheral nerves.


Jan 22, 2016 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Tumors of the Cranial/Spinal Nerves
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