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plexiform schwannoma

Wednesday 14 September 2005

Definition: Plexiform schwannoma is a rare variant of Schwann cell tumor. Occurring in either conventional or cellular type. They are characterized either grossly or histologically by a plexiform pattern of intraneural growth often with multinodularity.

Ordinary as well as plexiform schwannoma typically arise in superficial soft tissues and show a predilection for the head and neck region.

Infrequent examples arise in the setting of neurofibromatosis type 2 (NF2) or schwannomatosis.

Plexiform schwannoma represented 4.3% of all schwannomas, 23% of head and neck region examples, 15% of cutaneous schwannomas, and lastly, 2% of 322 oral nerve sheath tumors. Furthermore, the association with neurofibromatosis type 2 and with schwannomatosis was 5% each. (#18439936#)

Plexiform schwannoma (PS) is one of the least common histologic variants of schwannoma. It shows a plexiform growth pattern and typically occurs in the dermis and subcutaneous tissue.

This rare variant of schwannoma is characterized by a interconnecting multinodular growth mimicking a plexiform neurofibroma.

Only 5% of schwannomas have a plexiform or multinodular growth pattern. Unlike neurofibromas, this pattern is not strongly associated with neurofibromatosis type 1 (NF1) or neurofinromatosis type 2 (NF2).

Plexiform schwannomas usually are superficial, and located in the dermis or subcutaneous tissue. They are frequently cellular with hyperchromatic nuclei and increased mitotic figures. There is usually no/minimal necrosis or myxoid change. All tumors show strong and diffuse S100 immunoreactivity of the nodules, with no staining of the intervening stroma.

Plexiform neurofibromas can be very large and can cause pain, disfigurement, neurological and other clinical deficits.

While dermal neurofibromas originate in nerves in the skin, plexiform neurofibromas can grow from nerves in the skin or from more internal nerve bundles.

Internal plexiform neurofibromas are very difficult to remove completely because they extend through multiple layers of tissue and the attempt would damage healthy tissue or organs.

Plexiform neurofibromas also have the potential to cause sever clinical complications if they occur in certain areas.

In addition, about 10% of plexiform neurofibromas undergo malignant transformation. This transformation turns the plexiform neurofibroma into a malignant peripheral nerve sheath tumor (MPNST).

Synopsis

- age range: 5 months - 61 years of age
- conventional pattern
- cellular pattern

  • hyperchromatic nuclei
  • increased mitoses
  • plexiform growth

- mixed pattern

The plexiform schwannoma has a superficial resemblance to the plexiform neurofibroma with multiple interlacing and interconnecting fascicles and nodules, composed predominantly of Antoni A-type tissue.

Most tumors occur in the dermis and subcutis. A deep-seated variant has also been described.

In comparison with the superficial variety, the deep variant has a predilection for females, can occur in a congenital setting, and can show necrosis and myxoid change.

A further subset of plexiform schwannomas occurs in a congenital or childhood setting. It was previously considered a form of malignant peripheral nerve sheath tumor (MPNST).

Despite their cellular pleomorphism they are now known to have a benign behavior.

Variants

- superficial plexiform schwannoma (dermis and hypodermis)

  • extensive plexiform schwannoma

- deep-seated plexiform schwannoma (#16006798#)

Differential diagnosis

- plexiform neurofibroma

  • Plexiform neurofibromas almost always develop during early childhood and are considered pathognomonic for neurofibromatosis type 1. They are associated with grossly enlarged and tortuous nerves.
  • Microscopically, they are hypocellular with a myxoid background and lack the biphasic pattern seen in schwannomas. However, they occasionally show nuclear palisading.
  • Although neurofibromas are S100 immunoreactive, there is only staining of scattered cells that are diffusely throughout the lesion. In contrast, schwannomas show strong staining of the tumor nodules and no staining of the intervening stroma.

- malignant peripheral nerve sheath tumor (MPNST).

  • The cellularity, mitotic activity and atypia of plexiform schwannomas is also suggestive of MPNST, which may be multinodular, particularly if it arises from a plexiform neurofibroma.
  • Before diagnosing a plexiform MPNST, it is recommended to sample the tumor extensively to rule out a plexiform schwannoma.
  • S100 staining may be somewhat helpful, as MPNSTs typically show negative or weak staining.

Localization

- superficial PS
- deep-seated PS

  • extremities
  • retroperitoneum/pelvis
  • trunk
  • parotid
  • vulva
  • thoracic esophagus

Prognosis

- deep-seated PS

  • local recurrence (50%)
  • Worrisome morphologic features
  • increased cellularity (68%)
  • mild to moderate pleomorphism (50%)
  • mitotic activity (93%) ranging from 1 to 10 MF/10 high power fields (HPFs)

Immunohistochemical stains

- S-100 protein (strong and diffuse positivity)

Ultrastructure

- schwannian differentiation

Cytogenetics

- trisomy 17 (#15041228#)
- trisomy 18 (#15041228#)

See also

- peripheral nerve sheath tumors (schwannian tumors)

References

- Plexiform schwannoma: a clinicopathologic overview with emphasis on the head and neck region. Berg JC, Scheithauer BW, Spinner RJ, Allen CM, Koutlas IG. Hum Pathol. 2008 May;39(5):633-40. PMID: #18439936#

- Neurofibromatosis type 2 in an infant with multiple plexiform schwannomas as first symptom. Miyakawa T, Kamada N, Kobayashi T, Hirano K, Fujii K, Sasahara Y, Nagai Y, Shinkai H. J Dermatol. 2007 Jan;34(1):60-4. PMID: #17204104#

- Contiguous conventional and plexiform schwannomas. Report of two cases. White JB, Scheithauer BW, Amrami KK, Babovic-Vuksanovic D, Spinner RJ. J Neurosurg. 2006 Feb;104(2):319-24. PMID: #16509508#

- Neurofibromatosis type 2 with multiple plexiform schwannomas.
Lim HS, Jung J, Chung KY. Int J Dermatol. 2004 May;43(5):336-40. PMID: #15117362#

- 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#

- Joste NE, Racz MI, Montgomery KD, Haines S, Pitcher JD. Clonal chromosome abnormalities in a plexiform cellular schwannoma. Cancer Genet Cytogenet. 2004 Apr 1;150(1):73-7. PMID: #15041228#

- 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#

- Woodruff JM, Marshall ML, Godwin TA, Funkhouser JW, Thompson NJ, Erlandson RA. Plexiform (multinodular) schwannoma. A tumor simulating the plexiform neurofibroma. Am J Surg Pathol. 1983 Oct;7(7):691-7. PMID: #6638259#

- Plexiform (multinodular) schwannoma. A tumor simulating the plexiform neurofibroma. Woodruff JM, Marshall ML, Godwin TA, Funkhouser JW, Thompson NJ, Erlandson RA. Am J Surg Pathol. 1983 Oct;7(7):691-7. PMID: #6638259#

Portfolio

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  • Plexiform schwannoma
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  • Plexiform schwannoma (NF)
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  • Plexiform schwannoma (S100)
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  • Plexiform schwannoma (S100)
  • Plexiform schwannoma (NF)