Soft tissue

Peripheral nerve

Other benign

Schwannoma



Last author update: 4 January 2022
Last staff update: 2 February 2022

Copyright: 2002-2022, PathologyOutlines.com, Inc.

PubMed Search: Schwannoma[TI] soft tissue free full text[sb] pathology

Engy Abdellatif, M.B.B.Ch., M.D., Ph.D.
Jose G. Mantilla, M.D.
Page views in 2021: 75,174
Page views in 2022 to date: 46,555
Cite this page: Abdellatif E, Kamel D, Mantilla JG. Schwannoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueschwannoma.html. Accessed July 3rd, 2022.
Definition / general
  • Benign nerve sheath tumor arising from differentiated Schwann cells
Essential features
  • Encapsulated, well circumscribed
  • Most cases have a zonal pattern composed of cellular areas (Antoni A) with nuclear palisading (Verocay bodies) and a hypocellular component (Antoni B)
Terminology
  • Neurilemoma (acceptable)
ICD coding
  • ICD-10: D36.10 - benign neoplasm of peripheral nerves and autonomic nervous system, unspecified
Epidemiology
  • All ages can be affected
  • More common in 30 - 60 years of age
  • M = F
  • 90% are sporadic, 3% with neurofibromatosis type 2, 2% with schwannomatosis, 5% with meningiomatosis with or without neurofibromatosis type 2 (StatPearls: Schwannoma [Accessed 10 November 2021])
Sites
  • More frequently on the limbs with a predilection to the upper limbs, followed by the head and neck area, including the oral cavity, orbit and salivary glands
  • Deeply seated tumors are mainly in the posterior mediastinum and retroperitoneum
  • Other areas include posterior spinal roots, bone, gastrointestinal tract, pancreas, liver, thyroid, adrenal glands and lymph nodes
  • Rare sites include penis and vulva (Urol Ann 2017;9:301, World J Surg Oncol 2015;13:139)
Pathophysiology
  • May occur spontaneously
  • Can occur in familial tumor syndromes, such as neurofibromatosis type 2 (NF2), schwannomatosis or Carney complex (StatPearls: Carney Complex [Accessed 13 August 2018])
  • Loss of function of the tumor suppressor gene merlin (schwannomin)
    • Direct genetic change involving the NF2 gene on chromosome 22 or secondarily to merlin inactivation
    • Can occur in NF2 and spontaneous schwannomas
    • Can cause other neoplasms including meningioma, mesothelioma, glioma multiforme and carcinomas of breast, colon and rectum, kidney (clear cell type), liver, prostate and skin
Clinical features
  • Pain and neurological symptoms are uncommon unless the tumor is large
  • Tumor waxes and wanes in size, which may be related to cystic degeneration (J Lab Physicians 2013;5:60)
Diagnosis
  • Histologic findings in the appropriate clinical and imaging context
Radiology description
  • Well circumscribed masses that displace adjacent structures without direct invasion
  • Cystic and fatty degeneration can be seen
  • Hemorrhage and calcification are less frequent
  • Cystic degeneration or hemorrhage can be seen as areas of heterogeneity in large tumors (Radiographics 2004;24:1477, Radiographics 1999;19:1253)
Prognostic factors
Case reports
Treatment
  • Surgical excision is the treatment of choice
  • Local recurrence is uncommon
  • Delayed facial nerve palsy can occur after surgical removal of vestibular schwannoma (Neurosurgery 2016;78:251)
Clinical images

Contributed by Mark R. Wick, M.D.

Well circumscribed cutaneous mass

Gross description
  • Usually solitary
  • Most lesions are completely encapsulated
  • Nerve of origin may be present at the periphery - does not penetrate substance of tumor
  • Large tumors have an eccentric position in relation to the nerve
  • Cut section is light tan and glistening and may show yellow patches
  • Large, longstanding tumors may be cystic
  • Areas of hemorrhage may be seen (Goldblum: Enzinger and Weiss's Soft Tissue Tumors, 7th Edition, 2020)
Gross images

Contributed by Jose G. Mantilla, M.D., Mark R. Wick, M.D. and Case #334
Lesion associated with intercostal nerve

Lesion associated with intercostal nerve

Well circumscribed, homogeneous lesion

Well circumscribed, homogeneous lesion

Ancient schwannoma, cut section

Plexiform schwannoma

Microscopic (histologic) description
  • Biphasic: compact hypercellular Antoni A areas and myxoid hypocellular Antoni B areas (may be absent in small tumors)
  • Nuclear palisading around fibrillary process (Verocay bodies) is often seen in cellular areas
  • Cells are narrow, elongated and wavy with tapered ends interspersed with collagen fibers
  • Tumor cells have ill defined cytoplasm, dense chromatin
  • May have degenerative nuclear atypia, cystic degeneration and hemorrhage (ancient change)
  • Blood vessels may have thickened hyalinized walls and thrombi
  • Pseudoglandular spaces: uncommon; cystic spaces lined by Schwann cells; may represent degenerative Verocay bodies (Ann Diagn Pathol 2016;20:24, Arch Pathol Lab Med 2005;129:1106)
  • Amianthoid fibers or collagenous spherules: large nodular masses of collagen with radiating edges
  • Mitotic figures are rarely seen
  • No intratumoral axons
  • Tumors in the GI tract typically have a prominent lymphocytic rim
  • Variants:
    • Ancient schwannoma:
      • Features include hyalinization, nuclear atypia, hemosiderin deposition
      • Should not have conspicuous mitotic activity or other features suggestive of malignancy
    • Cellular schwannoma:
      • Composed entirely of Antoni A tissue and devoid of Verocay bodies
      • Most common in the paravertebral region
    • Epithelioid schwannoma:
      • Single or small groups of epithelioid schwann cells with moderate amphophilic cytoplasm and occasional nuclear pseudoinclusions (Am J Surg Pathol 2016;40:704):
      • Myxoid to hyalinized stroma, often with thick walled vessels
    • Microcystic / reticular variant (Am J Surg Pathol 2008;32:1080):
      • Has a preference for the GI tract and rarely in subcutaneous soft tissue
      • Formed of strands of bland spindle cells in a myxoid background, with various proportions of microcystic structures
      • No alternating Antoni A, Antoni B areas or Verocay bodies
    • Neuroblastoma-like variant:
    • Plexiform schwannoma:
      • Rare
      • May involve multiple nerve fascicles, making complete resection challenging
      • Typically associated with NF2 and schwannomatosis
Microscopic (histologic) images

Contributed by Dia Eldin Kamel, M.D., Ph.D. and Case #50

Schwannoma from right lateral border of tongue

S100+

Desmin-

SMA-

Left gluteus maximus schwannoma


Ancient changes

S100+

Schwannoma from the dorsum of the left hand

Plexiform schwannoma from the periosteum of the left tibia



Plexiform schwannoma:

Plexiform architecture

Nuclear palisading

Cellular areas

S100



Images hosted on other servers:

Microcystic / reticular schwannoma:

Plexiform growth pattern

Abundant eosinophilic cytoplasm

S100 positive

Virtual slides

Images hosted on other servers:

Schwannoma:

13 year old girl with cystic index finger lesion

45 year old man with thigh lump: H&E, S100

53 year old man with chest wall lump

77 year old woman with small tumor in stomach wall


Ancient schwannoma:

55 year old man with retroperitoneal tumor

Cytology description
  • Aggregates of spindled cells with indistinct cytoplasm and elongated nuclei with blunt pointed ends (World J Gastroenterol 2011;17:3459)
  • Ancient changes can show nuclear pleomorphism and occasionally nuclear inclusions
Cytology images

Case #59

Fine needle aspirate biopsy

Cell block



Images hosted on other servers:

Bland spindle cells

Microcystic structures

Positive stains
Negative stains
Electron microscopy description
  • Basal lamina consisting of electron dense material coats the surface of Schwann cells (Cancer 1981;48:1381, Acta Cytol 1983;27:441)
  • Elongated cells with continuous basal lamina, thin cytoplasmic processes, aggregates of intracytoplasmic microfibrils, peculiar intracytoplasmic lamellar bodies, extracellular long spacing collagen
  • Basal lamina is fragmented in Antoni B areas, suggesting that these areas are degenerated Antoni A areas
  • Contains lipid
  • Has characteristic Luse bodies (collagen fibers with abnormally long spacing exceeding 100 nm between electron dense bands)
Electron microscopy images

Images hosted on other servers:

Cellular schwannoma

Molecular / cytogenetics description
  • May occur spontaneously
  • Can occur in familial tumor syndromes such as neurofibromatosis type 2 (NF2), schwannomatosis or Carney complex
  • Can be caused by loss of function of the tumor suppressor gene, merlin (schwannomin)
  • Merlin acts as a tumor suppressor gene
    • Overexpression can hinder cell proliferation and the changes induced by oncogenes
    • Its downregulation leads to neoplastic transformation
  • Mutations affecting SMARCB1 have a role in the pathogenesis of a small subset of spinal schwannomas and biallelic inactivation of SMARCB1 may cooperate with deficiency of NF2 function (J Neurooncol 2018;137:33)
Sample pathology report
  • Chest wall mass, excision:
    • Schwannoma (see comment)
    • Tumor size: 3.5 cm in greatest dimension
    • Comment: Histologic sections contain an encapsulated neoplasm composed of cytologically bland spindle cells arranged in short fascicles, containing more densely cellular areas with nuclear palisading (Antoni A), alternating with paucicellular areas (Antoni B). There are focal areas of hemorrhage and myxoid degeneration. No histologic features of malignancy are identified.
Differential diagnosis
Board review style question #1
Which of the following immunohistochemical stains best differentiates schwannoma from neurofibroma?

  1. Calretinin
  2. CK5/6
  3. MNF116
  4. p63
  5. S100
Board review style answer #1
E. S100 shows strong and almost diffuse positivity with schwannoma in contrast to neurofibroma, which variably expresses the antigen due to the presence of other cell populations.

Comment Here

Reference: Schwannoma
Board review style question #2

Which of the following is true regarding the tumor represented in the picture?

  1. Its cytologic atypia is degenerative in nature
  2. The degree of cytologic atypia suggest malignant transformation
  3. Melanin pigment may be seen in some of these lesions
  4. These tumors are usually poorly circumscribed and difficult to excise
  5. Local recurrence and malignant transformation are common
Board review style answer #2
A. The picture represents schwannoma with degenerative changes (ancient schwannoma). Tumors with extensive degenerative changes may have extensive hyalinization with loss of their characteristic architectural features, as well as conspicuous degenerative cytologic atypia. Malignant transformation of schwannoma is exceedingly rare and most commonly reported in the setting of stereotactic radiation. Malignant melanotic nerve sheath tumor (formerly called melanotic schwannoma) is a rare tumor with metastatic potential, which often arises in the paraspinal region. Given its different biological behavior, it should not be labeled as schwannoma. Most schwannomas are encapsulated and easily separated from their nerve of origin. Local recurrence is rare after excision.

Comment Here

Reference: Schwannoma
Back to top
Image 01 Image 02