Schwannoma



Schwannoma


Amitabh Srivastava, MD





Key Facts


Terminology



  • Encapsulated, benign peripheral nerve sheath tumor composed predominantly of Schwann cells


Clinical Issues



  • Common between 20-50 years of age


  • Affects males and females equally


  • Surgical excision is curative


Macroscopic Features



  • Typically presents as eccentric mass loosely attached to underlying nerve


Microscopic Pathology



  • Hallmark: Variable amounts of hypercellular Antoni A and hypocellular Antoni B areas


  • Spindle cells in short fascicles in Antoni A areas


  • Loose matrix with cystic change and inflammatory cells in Antoni B areas


  • Bland nuclear features in most instances; degenerative nuclear atypia in “ancient” schwannoma


  • Cellular schwannoma may mimic MPNST


  • Plexiform schwannoma usually seen in children


  • Epithelioid schwannoma may be mistaken for smooth muscle tumor


  • Melanotic/psammomatous schwannoma often associated with Carney syndrome


  • Schwannomas in NF2 and schwannomatosis similar to sporadic tumors


  • Microcystic/reticular schwannoma has predilection for visceral location


Ancillary Tests



  • Diffuse, strong S100 positivity is characteristic






Schwannomas are well-circumscribed, encapsulated tumors and often arise as an eccentric mass loosely attached to an underlying nerve. The underlying nerve image wraps around the tumor in this example.






This tumor shows a thick peripheral capsule image and a yellow-white cut surface with foci of hemorrhage image.


TERMINOLOGY


Definitions



  • Encapsulated, benign peripheral nerve sheath tumor composed predominantly of Schwann cells


ETIOLOGY/PATHOGENESIS


Molecular Aberrations



  • Somatic NF2 gene mutations present in most tumors


  • Bilateral vestibular schwannomas occur in setting of germline NF2 gene mutations


CLINICAL ISSUES


Epidemiology



  • Incidence



    • 90% are sporadic


    • 10% are syndromic



      • About 3% with neurofibromatosis type 2 (NF2)


      • 2% with schwannomatosis


      • 5% with multiple meningiomas


      • Rarely in association with neurofibromatosis type 1 (NF1)


  • Age



    • All ages


    • Common between 20-50 years of age


  • Gender



    • Affects males and females equally


Site



  • Head & neck


  • Upper and lower extremities


  • Deep-seated tumors occur in mediastinum and retroperitoneum


Presentation



  • Slow growing


  • Painless mass



    • Large tumors may be painful


  • Cystic tumors may show fluctuation in size


Treatment



  • Surgical excision is curative


Prognosis



  • Excellent


Multiple Schwannoma Syndromes



  • Neurofibromatosis type 2



    • Autosomal dominant condition


    • Incidence around 1:30,000-40,000


    • Inactivating germline mutations of NF2 gene on chromosome 22


    • Bilateral vestibular schwannomas are characteristic


    • Schwannomas involving other cranial nerves may be present


    • CNS tumors like meningioma, ependymoma, and gliomas are also part of disease spectrum


    • Schwannomas in NF2 resemble their sporadic counterparts


  • Schwannomatosis



    • Not associated with germline mutations in NF1 or NF2 genes


    • Autosomal dominant inheritance with incomplete penetrance


    • Both sexes affected equally


    • Patients do not develop bilateral vestibular schwannomas or CNS tumors seen in NF2


    • Locus of disease mapped to chromosome 22 proximal to NF2 gene


    • Morphology similar to sporadic schwannomas


MACROSCOPIC FEATURES


General Features



  • Surrounded by true capsule consisting of epineurium


  • Eccentric mass loosely attached to underlying nerve




  • Small tumors may be fusiform in shape and mimic neurofibroma


  • Dumbbell-shaped tumors occur in vertebral canal usually in posterior mediastinum


  • Cut surface is pink, white-yellow


  • Large tumors may show cystic change, hemorrhage, or calcification


Size



  • Variable


MICROSCOPIC PATHOLOGY


Histologic Features



  • Uninodular mass with fibrous capsule


  • Hallmark: Variable amounts of hypercellular Antoni A and hypocellular Antoni B areas


  • Antoni A



    • Spindle cells in short fascicles


    • Plump nuclei, indistinct cytoplasmic borders


    • Intranuclear vacuoles in some tumors


    • Nuclear palisading or whorling


    • Verocay bodies



      • Compact rows of palisaded nuclei separated by fibrillary processes


  • Antoni B



    • Spindle or oval cells


    • Loose matrix with cystic change and inflammatory cells


    • Large vessels with thick hyalinized walls and luminal thrombi


  • Benign epithelial structures and glands may be present in rare instances


Cytologic Features



  • Bland nuclear features in most instances

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Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Schwannoma

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