Schwannoma

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, biphenotypic sinonasal sarcoma
IHC	S-100 +ve, EMA -ve, CD34 +ve
Site	soft tissue - peripheral nerve sheath tumours
Syndromes	neurofibromatosis type 2, Carney complex (psammomatous melanotic schwannoma), schwannomatosis
Prevalence	common
Prognosis	good
Clin. DDx	meningioma - esp. at cerebellopontine angle

Schwannoma is a relatively common peripheral nerve sheath tumour.

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.
• often encapsulated 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.
• Occurs at all ages.

Macro

• Usu. encapsulated.
• Cystic.
• Yellow patches on white surface.
  • Variable lipidization.

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.
• Reticulin stain +ve (around individual cells).

Notes:

• Tumour does not smear well.
• Antoni A: may look somewhat like scattered matchsticks.
• Hybrid Schwannoma / Neurofibroma are overrepresented in hereditary conditions.

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.
• Biphenotypic sinonasal sarcoma - head and neck.

Images

• 

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

• 

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

• 

  Antoni-A pattern in cerebelloponine angle schwannoma. (WC/jensflorian)

• 

  Antoni-A pattern in cerebelloponine angle schwannoma.(WC/jensflorian)

• 

  Nerve root schwannoma - intermed. mag. (WC)

• 

  S-100 immunostain in schwannoma. (WC/Ed Uthman)

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.
• Usu. <4 mitoses in 10 HPF (see HPFitis).
• Absence of Verocay bodies.
• Usu paravertebral location.

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).

• 

  Psammomatous melanotic schwannoma - high mag. (WC)

IHC

Features:

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

Others:

• Beta-catenin +ve -- not nuclear.

Molecular

Overview:

• Most common: NF2 (in Vestibular Schwannoma up to84%).
• less common: ARID1A, ARID1B, DDR, TSC1, TSC2, CDC27 and USP8.
• SH3PXD2A-HTRA1 fusions (10%).

• INI1 mosaic pattern in familiar schwannomatosis.
• LZTR1-associated vestibular schwannomas.

Molecular subgroups:

• Group 1: vestibular (has significant higher rate of 22q loss).
• Group 2: spinal.

Sign out

Lesion, Right Ulnar Nerve, Excision:
     - Schwannoma.

Block letters

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.