Peripheral nerve sheath tumours

Peripheral nerve sheath tumours, abbreviated PNSTs, are common in neuropathology and occasionally show-up elsewhere. A very common PNST is the schwannoma.

Classification

A classification:

• Benign:
  • Schwannoma.
  • Neurofibroma.
  • Perineurioma.
  • Traumatic neuroma.
• Malignant:
  • Malignant peripheral nerve sheath tumour (MPNST).

Specific diagnoses

Schwannoma

Main article: Schwannoma

Perineurioma

General

• Benign tumour derived from perineurial cells (intraneural or soft tissue).
  • ICD-O 9571/0
  • WHO grade I
• Rarely malignant soft tissue perineurioma.

Variant:

• Reticular perineurioma.

Macroscopy

• Intraneural perineurioma: segmental tubular enlargement of the nerve.
• Soft tissue perineurioma: Well circumscribed, but not encapsulated.

Microscopic

Features:

• Perineural epithelioid cells.
  • Abundant pale, fluffy appearing cytoplasm.

Note:

• May be intraneural.
  • Typical pseudo-onion bulbs.
  • Long considered hypertrophic neuropathy.
  • Rare (less than 1% of all nerve sheath tumours).

DDx:

• Neuroma.
• Neurofibroma.
• Schwannoma.
  • S100 +ve, EMA -ve.
• Liposarcoma - reticular perineurioma.

Images:

• Perineurioma (conganat.org).

• 

  Pseudo-onion bulbs in a intraneural perioneurioma (WC/jensflorian)

IHC

Features:

• S100 -ve.
• EMA +ve.
• CD34 ~65% +ve.

Traumatic neuroma

General

• Consequence of trauma - diagnosis requires history of trauma.
  • May mimic a cancer recurrence at the site of a surgery.

Microscopic

Features:

• +/-Nerve - that was injured.
• Grouping of disordered nerve fibre bundles in fibrous tissue (collagen) - key feature.
• +/-Myxoid change.
• +/-Axonal swellings (ovoid pink/purple blobs).

DDx:

• Morton neuroma (foot).

Images:

• Traumatic neuroma (nih.gov).
• Traumatic neuroma - several images (upmc.edu).
• Traumatic neuroma (sarcomaimages.com).
• Traumatic neuroma (nih.gov).
• Neuroma (nih.gov).

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SOFT TISSUE LESION, RIGHT WRIST, EXCISION:
- TRAUMATIC NEUROMA.
- BENIGN FIBROADIPOSE TISSUE.

Micro

The sections show disordered nerve fibre bundles in fibrous tissue.

Palisaded encapsulated neuroma

• Abbreviated PEN.
• AKA palisaded and encapsulated neuroma.
• AKA solitary circumscribed neuroma.

General

• Flesh-colour papule - classically on the face.
• Isolated finding - not associated with a systemic disease or malignancy.
• Superficial skin papule.
• It is considered hyperplastic rather than neoplastic.

Microscopic

Features:

• Encapsulated dermal spindle cell lesion.
  • Fasciular arrangement.
  • Neural-type spindle cells:
    1. Not vacuolated.
    2. Nuclei have pointy ends.
    3. Sometimes epitheloid appearance.
• Intralesional clefts.
  • Useful to differentiate from schwannoma.

DDx:

• Schwannoma:
  • No intralesional clefts.
  • More variability in the cellularity.
  • May be deep.

Other considerations:

• Leiomyoma - cytoplasm not vacuolated, nuclei more elliptical.

Images:

• PEN (cdlib.org).

• 

  Palisaded and encapsulated neuroma (Ed Uthman)

• 

  PEN, S-100 staining (Ed Uthman)

IHC

Features:

• S100 +ve.
• EMA +ve (capsule of lesion).

Neurofibroma

Main article: Neurofibroma

Includes discussion of plexiform neurofibroma.

Neurothekeoma

• AKA myxoma of the nerve sheath, AKA nerve sheath myxoma.
• There is growing evidence that neurothekomas and dermal nerve sheath myxomas are distinct entities.

General

• Rare.
• Female > male.

Microscopic

Features:

• Superficial dermal lesion:
  • Usu. lobulated or micronodular architecture - key feature.
    • +/-Focal sheeting.
  • Spindle/epithelioid morphology with pale eosinophilic cytoplasm - key feature.
  • +/-Inflammation around lesion.
  • +/-Surrounded by collagen.

Notes:

• No atypia.
• Mitoses rare/none.
• Often poorly circumscribed.

Subtypes:

• Cellular.
• Myxoid.
• Intermediate.

DDx:

• Dermatofibroma.
• Angiomatoid fibrous histiocytoma -- have cystic blood filled spaces, inflammation.

Images:

• Neurothekeoma (WP).
• Neurothekeoma - several images (upmc.edu).
• Nerve sheath myxoma (dermpedia)]

IHC

Features:

• NKI/C3 (AKA NKI-C3) +ve.
• NSE +/-ve.

Others:

• Vimentin +ve.
• CD10 +ve.
• Microphthalmia transcription factor +ve.
• PGP9.5 +ve.

Exclusionary:

• S100 -ve.
  • Exclude other peripheral nerve sheath tumours. (???)
  • Myxoid variant +ve. ^{[citation needed]}

Malignant peripheral nerve sheath tumour

Main article: Malignant peripheral nerve sheath tumour

Malignant triton tumour

• Abbreviated MTT.
• AKA malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentiation.

General

• Rare.
• Considered to be a variant of MPNST.
• Prognosis worse that conventional MPNST.
  • Five year survival ~14%.
• Diagnosis may require clinical information, i.e. individual has a history of neurofibromatosis type 1 (NF1).

Note:

• A handful of benign triton tumours are reported; these are considered neuromuscular hamartomas.

Microscopic

Features - Woodruff criteria - all three required:

1. (a) Tumour arise from a peripheral nerve or (b) individual has NF1 or (c) lesion a metastasis arising in the context of (a) or (b).
2. Schwann cell tumour characteristics.
3. Rhabdomyoblasts.
   • Eccentric nucleus.
   • Moderate amount of eosinophilic cytoplasm.
   • +/-Cross-striations.

DDx:

• Malignant peripheral nerve sheath tumour.
• Adult fibrosarcoma.
• Synovial sarcoma.
• Rhabdomyosarcoma.
• Carcinosarcoma.

IHC

Features:

• S100 +ve/-ve -- usu. focal if positive.
• Leu-7 +ve/-ve.
• Myelin basic protein +ve/-ve.

Rhabdomyoblastic differentiation:

• Desmin.
• Actin.
• Myogenin.

EM

• +/-Sarcomeres.

Morton neuroma

AKA plantar interdigital neuroma.

Main article: Morton neuroma

See also

• Neuropathology.
• Gastrointestinal pathology.