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Case 386 - Discussion

Uploaded: 2010-04-18, Updated: 2010-04-18

Schwannoma

Clinical Futures

  • Peak age, 30-60 year-old, no sex predilection;

  • Most common sites: head, neck, flexor surfaces of the extremities;

  • Associated with NF2, on chromosome 22, that encodes a tumor suppressor gene, Merlin or Schwannomin.

Gross Findings

  • Most are solid, globular masses with the parent nerve embedded within the fibrous capsule;

  • Encapsulated with nodular or smooth surface;

  • Cut surface: lobulated , and tan or patchy yellow due to lipid accumulation;

  • May show degenerative changes, including marked lipidization, cystic changes, hemarrhage and calcification.

Microscopic Findings

  • Well-formed fibrous capsule;

  • Characteristic Antoni A and Antoni B patterns at various proportions;

  • Antoni A: compacted elongate cells with tapered, spindle-shaped nuclei, variable chromasia, abundant pink or blueish cytoplasm, and no discernible cell membrane. The cells are aligned and compactly disposed in broad bundles, interlacing fascicles or whorls. The Verocay bodies consist of nuclear clusters in palisaged patterns, in which well-regimented double rows of nuclei seperated by algined eosinophilic cell processes. The nuceli are serveral times larger than those in most of neurofibromas;

  • Antoni B: looaw-textured, cobweb meshwork of cells with multi-polar processes;

  • Thickened, hyalinized vessels, with perivascular hemosiderin, thrombosis or microhemorrhage

Subtypes

  • Cellular schwannoma: high cellularity, large Antoni A pattern, and absence of well-formed Verocay bodies;

  • Plexiform schwannoma: composed of exclusively Schwann cells and exhibits plexiform;

  • Psammomatous melanotic schwannoma: melanin-producing cells with features of Schwann cells in EM. S-100 and HMB-45 positive.

Differential Diagnosis

Schwannoma

 

Neurofibroma

NF2 association

NF1 association

Commonly in extremities

Commonly involves trunk

Nerve often identified

Nerve infrequently identified

Eccentric to nerve

Incorporates nerve

Globular

Globular, fusiform or diffuse

Encapsulated

No capsule

Occasionally cystic

Noncystic

Biphasic, Antoni A and B patterns

Uniphasic

Axons often absent

Axons often present

Palisading and Verocay bodies

No palisading, Wagner-Meissner or Pacinian-like corpuscles

Immunohistochemistry Straining

  • S-100 and vimentin, positive

  • GFAP and CD68, patchy positivity

  • CD34, only in Antoni B

  • Leu-7, variable

Election Microscopy

  • Prominent arrays of cell processes coated with basal lamina, and the processes are long, thin, closely packed and intertwined.

Cytogenetics

  • In NF2, mutation on NF2 / Merlin / Schwannomin.

Reference

  • AFIP, Tumor of the peripheral nervous system.