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deep-seated plexiform schwannoma

Tuesday 6 June 2006

Plexiform schwannoma (PS) is one of the least common histologic variants of schwannoma. Deep-seated PS is a rare, under-recognized PNST of deep soft tissue, typically not associated with neurofibromatosis.

Although commonly occurring in the extremities, they can be seen in other locations including the viscera. In contrast with the more common superficial (dermal and subcutaneous) tumors, deep PSs have a predilection for females, can occur in congenital settings, and can show necrosis and myxoid change.

Common worrisome histologic features seen in both groups include increased cellularity and mitoses.

Synospsis

- plexiform growth pattern
- typically occurs in the dermis and subcutaneous tissue
- conventional, cellular, or mixed appearance

  • frequent cellular appearance: hyperchromatic nuclei, increased mitoses

Localization:

- deep somatic soft tissue (extremities; retroperitoneum/pelvis; trunk; parotid; vulva)

- thoracic esophagus.

Predisposition

- no known association with neurofibromatosis

Prognosis

- local recurrence (50%)
- prognostic parameters

  • increased cellularity (68%)
  • mild to moderate pleomorphism (50%)
  • mitotic activity (93%) ranging from 1 to 10 MF/10 high power fields (HPFs)
  • focal necrosis (12%)
  • myxoid change was identified (18%)

Immunohistochemistry

- S-100 + (strong and diffuse) (100%)

Ultrastructure

- schwannian differentiation

Differential diagnosis

- plexiform neurofibromas
- malignant soft tissue tumors

References

- Agaram NP, Prakash S, Antonescu CR. Deep-seated plexiform schwannoma: a pathologic study of 16 cases and comparative analysis with the superficial variety. Am J Surg Pathol. 2005 Aug;29(8):1042-8. PMID: 16006798

- Woodruff JM, Scheithauer BW, Kurtkaya-Yapicier O, Raffel C, Amr SS, LaQuaglia MP, Antonescu CR. Congenital and childhood plexiform (multinodular) cellular schwannoma: a troublesome mimic of malignant peripheral nerve sheath tumor. Am J Surg Pathol. 2003 Oct;27(10):1321-9. PMID: 14508393