Schwannoma

Schwannoma is a relatively common peripheral nerve sheath tumour.

Schwannoma
Diagnosis in short
Schwannoma showing Antoni A and Antoni B areas. HPS stain.
LM	Antoni A areas (cellular, fibrillary, polar, elongated), Antoni B area (pauci-cellular, loose microcystic tissue), Verocay bodies (paucinuclear area surrounded by nuclei), hyaline thickened blood vessels, thick capsule. +/-peripheral lymphoid cuff (esp. GI tract)
Subtypes	conventional schwannoma, cellular schwannoma, plexiform schwannoma, melanotic schwannoma
LM DDx	meningioma, leiomyoma, GIST, intranodal palisaded myofibroblastoma, MPNST, neurofibroma
IHC	S-100 +ve, EMA -ve, CD34 +ve
Site	soft tissue - peripheral nerve sheath tumours
Syndromes	neurofibromatosis type 2, Carney complex (psammomatous melanotic schwannoma)
Prevalence	common
Prognosis	good
Clin. DDx	meningioma - esp. at cerebellopontine angle

At the cerebellopontine (CP) angle, they may be referred to as acoustic neuroma or vestibular schwannoma.

General

• A common neuropathology tumour that occasionally shows-up elsewhere.
• Tumour of tissue surrounding a nerve.
  • Axons adjacent to the tumour are normal... but may be compressed.
• May be a part of neurofibromatosis type 2.

Microscopic

Features:

• Antoni A:
  • Cellular.
  • 'Fibrillary, polar, elongated'.
• Antoni B:
  • Pauci-cellular.
  • Loose microcystic tissue.
• Verocay bodies - paucinuclear area surrounded by clusters of nuclei - diagnostic feature.
• Hyaline thickened blood vessels.
• Thick capsule.
• In the GI tract: classically have a peripheral lymphoid cuff.
• +/-Hemosiderin deposition within tumour.

Notes:

• Tumour does not smear well.
• Antoni A: may look somewhat like scattered matchsticks.

DDx:

• Meningioma.
• Intranodal palisaded myofibroblastoma - if surrounded by a rim of lymphoid tissue, i.e. intranodal.
• Leiomyoma.
• Gastrointestinal stromal tumour.
• MPNST - schwannoma with ancient change has no significant mitotic activity.
• Neurofibroma.

Images

• 

  Schwannoma - Antoni A & B - intermed. mag. (WC)

• 

  Scwhannoma - Antoni A & B - very high mag. (WC)

• 

  Psammomatous melanotic schwannoma - high mag. (WC)

• 

  Nerve root schwannoma - intermed. mag. (WC)

www:

• Antoni A (pathguy.com).
• Antoni A & Antoni B side-by-side (ajnr.org).
• Cystic schwannoma - several images (upmc.edu).

Schwannoma subtypes

There are four:

1. Conventional schwannoma.
2. Cellular schwannoma.
3. Plexiform schwannoma.
4. Melanotic schwannoma.

Conventional schwannoma

• Most common.

Cellular schwannoma

• May mimic MPNST.

Images:

• Cellular schwannoma (upmc.edu).

Plexiform schwannoma

• May mimic MPNST if cellular - esp. in childhood.

Images:

• 

  Plexiform schwannoma - low mag. (WC)

• 

  Plexiform schwannoma - high mag. (WC)

Melanotic schwannoma

• May be confused with melanoma.
• Psammomatous form (psammomatous melanotic schwannoma) associated with a heritable disorder (Carney complex).

Note:

• Carney complex:
  • Cutaneous lentigines.
  • Myxomas (skin (subcutaneous), subcutanous, heart).
  • Endocrine neoplasms.

Images:

• Psammomatous melanotic schwannoma - several images (upmc.edu).

IHC

Features:

• S-100 +ve.
• Glut1 +ve.
• CD34 +ve.
• Cytokeratins ~70% +ve.^{[citation needed]}
• SOX10 +ve.
  • -ve in synovial sarcoma, rhabdomyosarcoma, chondrosarcoma.
• EMA -ve. (???)
  • Usually +ve (~75% of the time) in meningiomas.

Others:

• Beta-catenin +ve -- not nuclear.

Sign out

LESION, LEFT ANTERIOR TIBIA, EXCISION:
- SCHWANNOMA.
- NEGATIVE FOR MALIGNANCY.

Micro

The sections show a soft tissue spindle cell lesion, with cellular fibrillary areas (Antoni A) and pauci-cellular microcystic areas (Antoni B). There are also pauci-nuclear areas surrounded by clusters of nuclei (Verocay bodies). Thick hyaline blood vessels are present within the lesion. There is no apparent nuclear atypia. Mitotic activity is not readily apparent. No nerve is seen adjacent to the lesion. The lesion is partially encapsulated by fibrous tissue. Focally, ink is seen on the lesional cells.

See also

• Peripheral nerve sheath tumours.