Schwannoma

Epidemiology:

• 20-50y usually

Common sites:

• intradural:
• cerebellopontine angle (attached to vestibular branch of the 8^th nerve) (acoustic neuroma)
• sensory nerves preferentially
• extradural:
• large nerve trunks
• flexor surfaces of extremities
• head & neck
• may occur in GI tract – most in stomach

Gross features:

• well-circumscribed, encapsulated
• firm
• grey
• lobulated / globoid
• may be attached to nerve or separate
• may have areas of cystic and xanthomatous change
• no necrosis
• GI schwannomas:
• Not encapsulated
• Mural nodule
• May be plexiform

Histologic features:

• well-circumscribed
• encapsulated
• may be attached to a nerve
• Mixture of Antoni A and B patterns
• Antoni A:
• Moderate to high cellularity
• Varocay bodies
• Nuclear-free zones between regions of nuclear palisading
• Antoni B:
• Less cellular
• Loose meshwork of cells
• Disorderly
• Microcysts
• Myxoid changes
• Cytology:
• Elongated with cytoplasmic processes
• Pale eosinophilic cytoplasm
• Regular oval nuclei
• Nuclear pleomorphism may be present
• Thickened or sclerotic vessel walls
• Whirling around vessels focally maybe
• Mitoses infrequent
• Degenerative changes (ancient schwannoma):
• Cyst formation
• Hyalinization
• Calcification
• Nuclear pleomorphism
• (Low mitotic activity)
• Cellular schwannoma (10%):
• cellular
• Mostly Antoni A
• Usually no well formed Verocay bodies
• Mitoses readily identified (<4 / 10HPF)
• Small foci of necrosis maybe
• May erode bone and recur locally
• Plexiform pattern (5%)
• Epithelioid schwannoma
• Glandular or benign epithelial structures maybe
• Xanthomatous change may be present – lipid-laden macrophages
• Vascular hyalinization may be present
• No axons within tumour
• Can they have fat in them?
• GI schwannomas:
• Not encapsulated
• Striking lymphoid cuff at periphery with germinal centres
• homogenous
• Intralesional lymphocytes and plasma cells sometimes
• Loosely / minimally palisaded (note: GISTS often display striking palisading)

Immunophenotype:

Marker:	Sensitivity:	Specificity:
S-100 (diffuse, strong)		Meningioma staining is generally not diffuse and strong
GFAP (occasional cells)
CD117 (neg)
EMA (neg)		Meningioma is generally positive

Molecular features:

• Biallelic inactivation of NF2 gene (22q12) (2/3 of schwannomas)
• monosomy 22 (2/3 of karyotypically abnormal cases)
• mutations in NF2 (sporadic)
• other recurrent karyotypic abnormalities:
• -12
• -15
• -X
• -Y
• +5
• +7
• +20
• Neurofibromatosis type II (familial)

Other features:

• EM :
• Attenuated cell processes in layers adjacent to cell body
• basement membrane deposits (basal lamina) encasing single cells and processes
• Long-spacing collagen
• Associated with neurofibromatosis type 2
• benign
• Malignant change is extremely rare

References:

• Robbins 2005
• Gastrointestinal and Liver Pathology 2005
• Silverberg SG, DeLellis RA, Frable WJ, LiVolsi VA, Wick MR. Silverberg's Principles and Practice of Surgical Pathology and Cytopathology: 2-Volume Set. 4th ed. Churchill Livingstone; 2005:2656.