Neurosurgery notes/Tumours/Cranial and paraspinal nerve tumours/Perineurioma

Perineurioma

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Cranial and paraspinal nerve tumours

Definition

  • A tumour composed entirely of neoplastic perineurial cells
Epineurium Perineurium Endoneurium Schwann Adipose tissue Artery and vein Loose connective tissue Fascicle Axon

Numbers

  • Both rare, (1% of nerve sheath and soft tissue neoplasms)

Origin

  • Perineurial cells:
    • Forms the perineurium
    • AKA: myoeptheliod myofibroblasts

Genetic profile

  • Monosomy Chr 22
  • Loss of Chr 13
  • Loss of Chr 10
  • Deletion of 22q (NF2)

Two subtypes

Feature
Soft tissue perineuriomas
Intraneural perineuriomas
Grading
Variable (WHO I-III)
Benign WHO I
Age group
Adults
Adolescence/early adult
Sex predilection
Female (2:1)
None
Localisation
Deep soft tissue, no associated with nerves
Affects peripheral nerve of the extremities
Clinical features
Nonspecific mass effect
Motor weakness > sensory loss
Macroscopic
Small (1.5-7cm)
Larger (<10cm)

Soft tissue perineuriomas

  • General
    • Not associated with nerve, are variably whorled, and are usually benign.
    • Malignant soft tissue perineurioma is a rare variant of malignant peripheral nerve sheath tumour displaying perineurial differentiation
  • Definition
    • Essential:
      • Slender spindle cells with bipolar cytoplasmic processes AND
      • Storiform and/or whorled architecture AND
      • Tumour cells are positive for at least one perineurial antigen (EMA, claudin-1, GLUT1) and negative for S100
  • CNS WHO grading
    • Range from benign (corresponding histologically to WHO grade I) to variably malignant (corresponding histologically to WHO grades ll-lll).
  • Numbers
    • Occur in adults,
    • Predominantly females (with a female-to-male ratio of 2:1)
  • Clinical features
    • Non-specific mass effects
  • Localisation
    • Deep soft tissue and are grossly unassociated with nerve.
    • Visceral involvement is rare
  • Histopathology
    • Macroscopic
      • Solitary, generally small (1.5-7 cm)
      • Well circumscribed
      • Encapsulated
      • On the cut surface, they are firm and greyish white to infrequently focally myxoid.
      • Malignant soft tissue perineuriomas are usually not associated with a nerve and may feature invasive growth and variable necrosis.
    • Microscopic
      • Composed of spindled, wavy cells with remarkably thin cytoplasmic processes arranged in lamellae and embedded in collagen fibres.
      • Crude whorls or storiform arrangements are commonly seen
      • Aggregates of collagen fibres are often encircled by long, remarkably narrow tumour cell processes.
      • Nuclei are elongate with tapered ends and are often curved or wrinkled.
      • Degenerative atypia (i.e. nuclear pleomorphism, hyperchromasia, and cytoplasmic-nuclear inclusions) is seen primarily in long-standing tumours
      • Variable mitosis
    • Immunophenotype
      • Positive stains
        • Claudin-1
        • GLUT1
      • Negative stains
        • CD34
        • MUC4
        • S100
    • Immunophenotype for malignant soft tissue perineuriomas
      • Positive: EMA staining
      • Negative: S100
  • Prognosis
    • Malignant examples of soft tissue perineuriomas prone to recurrence and occasional metastasis
      • Malignant perineuriomas are far less prone to metastasize than are conventional malignant peripheral nerve sheath tumours
    • Benign examples are usually amenable to gross total removal
      • Rare to metastasize

Intraneural perineuriomas

  • General
    • Used to be considered a form of hypertrophic neuropathy
    • The solitary expansion of peripheral nerves, due to involvement of one of more nerve fascicles.
  • Definition
    • Essential:
      • Pseudo-onion bulb pattern on cross-section, with axons in the centre AND
      • Tumour cells are positive for at least one perineurial antigen (EMA, claudin-1, GLUT1) and negative for S100
  • CNS WHO grading
    • WHO I
  • Numbers
    • Adolescence or early adulthood
    • No sex predilection.
  • Localization
    • Intraneural perineuriomas primarily affect peripheral nerves of the extremities; cranial nerve lesions are rare
  • Clinical features
    • Progressive muscle weakness (with or without obvious atrophy) > sensory disturbances.
  • Radiological
    • Intraneural perineuriomas appear as fusiform enlargement of a nerve with increased T2 signal and contrast enhancement
  • Histopathology
    • Macroscopic
      • Intraneural perineurioma produces a segmental, tubular, several-fold enlargement of the affected nerve
      • Individual nerve fascicles appear coarse and pale
      • Most lesions are < 10 cm long
      • Although multiple fascicles are often involved, a bag-of worms plexiform growth is not seen.
    • Microscopic
      • Consists of neoplastic perineurial cells proliferating throughout the endoneurium.
        • Cells form concentric layers around axons, causing enlargement of fascicles and forming characteristic pseudo-onion bulbs
        notion image
      • Particularly large whorls can envelop numerous nerve fibres.
      • Proliferation of perineurial cells occurs at endoneurium > perineurium
      • Sometimes adjacent onion bulb fuse with each other forming a complex endoneurial network
      • When tumour grows, the remaining myelin gets lesser and lesser
    • Immunophenotype
      • Positive stains
        • Perineural cells
          • Vimentin
          • EMA (epithelial membrane antigen)
          • Collagen IV
          • Laminin
        • Axons in the centre of the pseudo onions
          • NFP
          • S100
        • CD34 (33%)
      • Negative stains
        • S100
        • Desmin
      • Ki-67 proliferation index of 5-15%
  • Prognosis:
    • Do not have a tendency to recur or metastasize