CNS & pituitary tumors

Other tumors

Schwannoma


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Deputy Editor-in-Chief: Chunyu Cai, M.D., Ph.D.
Valeria Barresi, M.D., Ph.D.

Last author update: 17 March 2023
Last staff update: 11 October 2023

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PubMed Search: Schwannoma

Valeria Barresi, M.D., Ph.D.
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Cite this page: Barresi V. Schwannoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorschwannoma.html. Accessed February 22nd, 2024.
Definition / general
  • Schwannoma is a benign nerve sheath tumor composed of differentiated neoplastic Schwann cells
  • Classified as CNS WHO grade 1
Essential features
  • CNS primary tumor mostly occurring in the spine / spinal nerve roots (intradural, extramedullary) and vestibular division of the eighth cranial nerve within the cerebellopontine angle
  • Multiple tumors in patients with neurofibromatosis type 2 (NF2, bilateral vestibular schwannomas) or schwannomatosis
  • Excellent prognosis with nearly absent recurrence after gross total resection
  • Malignant transformation is exceptionally rare
  • Biphasic, encapsulated tumor composed of compact areas with spindle cells (Antoni A) and palisading nuclei (Verocay bodies) and loose microcystic areas with lipid laden macrophages (Antoni B)
Terminology
  • Neurilemmoma (not recommended)
  • Acoustic neuroma (not recommended)
ICD coding
  • ICD-O: 9560/0 - schwannoma, NOS
  • ICD-11: 2A02.3 & XH98Z3 - benign neoplasm of cranial nerves & schwannoma, NOS
Epidemiology
Sites
  • Most common sites in the CNS:
    • Spine, where it is typically intradural and extramedullary
    • Vestibular division of the eighth cranial nerve (Neuro Oncol 2022;24:v1)
Pathophysiology
  • NF2 inactivating mutation (frameshift and nonsense) and loss of the remaining wild type allele on chromosome 22, in 50 - 75% of sporadic schwannomas (J Neurosurg 2018;128:911)
  • Germline pathogenic NF2 mutation in schwannomas associated with neurofibromatosis type 2 (Genet Med 2022;24:1967)
  • Germline mutations of either SMARCB1 or LZTR1 on chromosome 22, followed by a somatic mutation in NF2 along with the deletion of the other chromosome 22 in schwannomas associated with schwannomatosis (Neurology 2015;84:141, Clin Genet 2020;97:376, Genet Med 2022;24:1967)
Etiology
Clinical features
  • Symptoms depend on the anatomical site of the tumor:
    • Tinnitus, unilateral sensorineural hearing loss, vertigo or disequilibrium in patients with vestibular schwannoma (J Neurosurg 2022 Dec 2 [Epub ahead of print])
    • Sensory or motor symptoms in patients with spinal schwannoma
Diagnosis
  • Based on imaging (CT, MRI) / biopsy / resection specimen
Radiology description
  • Well circumscribed masses that displace adjacent structures without direct invasion
  • On MRI, it may be
Radiology images

Contributed by Valeria Barresi, M.D., Ph.D.

T1 weighted MRI

FLAIR MRI

T2 weighted MRI

Prognostic factors
Case reports
Treatment
  • Observation, radiosurgery, surgery or surgery followed by radiosurgery, depending on symptoms, tumor size and association with neurofibromatosis type 2 (Neurooncol Pract 2016;3:281)
  • Bevacizumab is considered as an option in patients with neurofibromatosis type 2 (Neuro Oncol 2020;22:31)
Gross description
Gross images

Images hosted on other servers:

Surgically resected schwannoma

Acoustic schwannoma

Fish flesh tan cut surface

Frozen section description
  • Admixture of compact and loose areas, Verocay bodies and wavy / spindled nuclei with pointed ends are useful diagnostic clues in the differential diagnosis versus other spindle cell tumors (e.g., meningioma, ependymoma, sarcoma, solitary fibrous tumor) (Arch Pathol Lab Med 2007;131:1532)
  • Additional features: hyalinized blood vessels, chronic inflammatory infiltrates along capsule, hemosiderin
  • Additional clues:
    • Differential diagnosis versus ependymoma: absence of fibrillary background and perivascular pseudorosettes
    • Differential diagnosis versus meningioma: lack of psammoma bodies, whorls or epithelioid syncytia
    • Differential diagnosis versus sarcoma: in malignant sarcomas, mitoses are more commonly encountered, nuclear atypia is more uniformly widespread and necrosis may be present (Arch Pathol Lab Med 2007;131:1532)
    • Differential diagnosis versus solitary fibrous tumor: lack of staghorn vessels
Intraoperative frozen / smear cytology images

Contributed by Valeria Barresi, M.D., Ph.D.

Alternating compact and loose areas

Compact areas composed of spindle cells

Cohesive clusters with sharp borders

Spindle cell nuclei in fibrillary matrix

Microscopic (histologic) description
  • Spindle cell tumo (usually biphasic) and composed of compact hypercellular areas (Antoni A tissue) showing nuclear palisading (Verocay bodies) and loose microcystic areas (Antoni B tissue) with collection of lipid laden histiocytes and thick walled hyalinized blood vessels (Surg Neurol Int 2020;11:454)
  • Lymphoid aggregates maybe seen peripherally or in a subcapsular distribution
  • Mitoses or focal degenerative atypia may be present
  • Ancient subtype: characterized by scattered atypical or bizarre nuclei
  • Cellular subtype: composed exclusively or predominantly by Antoni A tissue and devoid of Verocay bodies
  • Epithelioid subtype: characterized by epithelioid cells with amphophilic or eosinophilic cytoplasm and uniform round nuclei with inconspicuous nucleoli
Microscopic (histologic) images

Contributed by Valeria Barresi, M.D., Ph.D.

Compact and loose areas

Atypical nuclei

Lipid laden histiocytes

Verocay bodies

S100

SOX10

Cytology description
Positive stains
Molecular / cytogenetics description
Sample pathology report
  • Spine, tumor, resection:
    • Schwannoma, CNS WHO grade 1 (see comment)
    • Comment: Spindle cell tumor showing loose areas with lipid laden macrophages and compact areas with nuclear palisading.
Differential diagnosis
Board review style question #1

An intradural, extramedullary mass is found in the spine. Histological examination shows a tumor with compact areas composed of spindle cells alternating with loose areas with collection of lipid laden macrophages. What is the most likely diagnosis?

  1. Ependymoma
  2. Meningioma, fibrous subtype
  3. Schwannoma
  4. Solitary fibrous tumor
Board review style answer #1
C. Schwannoma. Fibrous meningioma may localize in the spine but it does not feature alternating compact and loose areas or lipid laden macrophages. Solitary fibrous tumor shows typical staghorn vessels, collagen fibers and neoplastic cells with oval nuclei. In spinal ependymoma, tumor cells have processes forming fibrillary areas around tumor vessels (pseudovascular rosettes) and they often dispose to form rosettes.

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Reference: Schwannoma
Board review style question #2
An extra-axial mass is found in the cerebellopontine angle. Histological examination shows a tumor with compact areas composed of spindle cells with nuclear palisading and scattered atypical nuclei and loose areas. No mitoses or necrosis are seen. At immunohistochemistry, tumor cells are extensively positive for SOX10 and S100 and negative for EMA, STAT6, GFAP. Which is the most likely diagnosis?

  1. Malignant peripheral nerve sheath tumor
  2. Meningioma, fibrous subtype
  3. Schwannoma, ancient subtype
  4. Solitary fibrous tumor
Board review style answer #2
C. Schwannoma, ancient subtype. Schwannoma is typically SOX10 and S100 positive and EMA, STAT6 and GFAP negative. Ancient subtype shows scattered atypical nuclei. Meningioma, fibrous subtype may be negative for EMA but it is negative for SOX10 or S100 staining. Solitary fibrous tumor is STAT6 positive and negative for SOX10. Malignant peripheral nerve sheath tumor is negative or has only patchy positivity for SOX10 and S100 and it shows brisk mitotic activity and mitoses.

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Reference: Schwannoma
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