Definition/General
Introduction:
Schwannoma is a benign nerve sheath tumor
It arises from Schwann cells
Represents 5% of benign soft tissue tumors
FNAC shows spindle cells with characteristic nuclear features.
Origin:
Originates from Schwann cells of peripheral nerves
Encapsulated tumor displacing nerve fascicles
Can arise from any peripheral nerve
Cranial nerves (especially CN VIII) commonly affected.
Classification:
WHO classification: Benign nerve sheath tumor
Types: Conventional schwannoma
Cellular schwannoma
Plexiform schwannoma
Epithelioid schwannoma
Ancient schwannoma.
Epidemiology:
Peak incidence 3rd-6th decades
Equal gender distribution
Solitary in 90% cases
Multiple schwannomas in NF2
Most common primary nerve tumor.
Clinical Features
Presentation:
Slowly growing mass
Usually painless
Mobile perpendicular to nerve
Fixed parallel to nerve
Tinel sign positive
Neurological deficits rare.
Symptoms:
Painless mass (80%)
Paresthesias
Pain (especially acoustic schwannoma)
Functional deficit (large tumors)
Hearing loss (acoustic)
Mass effect.
Risk Factors:
Neurofibromatosis type 2 (bilateral acoustic)
Schwannomatosis
Age 20-70 years
No gender predilection
Genetic mutations (NF2 gene).
Screening:
Clinical examination
MRI for localization
Nerve conduction studies
FNAC (with caution)
Genetic counseling (multiple lesions)
Audiometry (acoustic).
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Gross Description
Appearance:
Well-encapsulated mass
Fusiform shape
Gray-white cut surface
Whorled pattern
Cystic degeneration (ancient)
Yellow areas (lipid-rich).
Characteristics:
Smooth surface
Firm consistency
Attached to nerve
Displaces nerve fascicles
Hemorrhage and calcification (ancient)
Myxoid areas.
Size Location:
Head and neck (25%)
Extremities (50%)
Spinal nerves (20%)
Mediastinum (5%)
Size: 2-8 cm typically
Acoustic schwannoma: CPA angle.
Multifocality:
Solitary (90%)
Multiple in NF2 (10%)
Bilateral acoustic (pathognomonic of NF2)
Plexiform in schwannomatosis
Spinal multiple possible.
Microscopic Description
Histological Features:
FNAC shows spindle cells in cohesive clusters
Wavy, buckled nuclei
Elongated cell processes
Antoni A and B areas
Verocay bodies
No mitoses.
Cellular Characteristics:
Elongated spindle cells
Wavy, serpentine nuclei
Fine chromatin
Inconspicuous nucleoli
Eosinophilic cytoplasm
Cytoplasmic processes.
Architectural Patterns:
Cohesive fascicles
Palisading pattern
Streaming arrangement
Dense cellular areas (Antoni A)
Loose myxoid areas (Antoni B)
Clean background.
Grading Criteria:
Benign features
No grading system
Assessment: Nuclear morphology
Absence of mitoses
Uniform cellularity
Schwannian features.
Immunohistochemistry
Positive Markers:
S-100 protein - strongly positive (hallmark)
GFAP - positive
Vimentin - positive
Calretinin - positive
SOX10 - positive
Collagen IV - basement membrane.
Negative Markers:
Neurofilament - negative
EMA - negative
Cytokeratin - negative
Desmin - negative
CD34 - negative
Smooth muscle actin - negative.
Diagnostic Utility:
S-100 strong positivity diagnostic
SOX10 confirms neural crest origin
Differentiates from other spindle cell tumors
Ki-67 very low (<2%)
Reticulin surrounds individual cells.
Molecular Subtypes:
Conventional: S-100+ strong, SOX10+
Cellular: Same markers, higher cellularity
All variants: Strong S-100 expression
NF2-associated: Loss of merlin expression.
Molecular/Genetic
Genetic Mutations:
NF2 mutations (sporadic and NF2-associated)
SMARCB1 mutations (schwannomatosis)
LZTR1 mutations (schwannomatosis)
22q12 deletions
Merlin protein loss.
Molecular Markers:
NF2/merlin pathway alterations
mTOR pathway activation
Hippo pathway dysregulation
Low mutational burden
Chromosomal stability (most cases).
Prognostic Significance:
Excellent prognosis
No malignant potential
Recurrence rare after complete excision
Malignant transformation <1%
Functional preservation possible.
Therapeutic Targets:
Complete surgical excision
Nerve-sparing techniques
Observation (asymptomatic, small)
Stereotactic radiosurgery (acoustic)
mTOR inhibitors (investigational).
Differential Diagnosis
Similar Entities:
Neurofibroma
Malignant peripheral nerve sheath tumor
Perineurioma
Leiomyoma
Fibroma
Solitary fibrous tumor.
Distinguishing Features:
Schwannoma: S-100+ strong, encapsulated, displaces nerve
Neurofibroma: S-100+ weak, infiltrates nerve, CD34+
MPNST: S-100+ focal, cellular atypia, mitoses
Perineurioma: EMA+, claudin-1+
Leiomyoma: SMA+, desmin+.
Diagnostic Challenges:
Distinguishing from neurofibroma on cytology
Ancient schwannoma with atypia
Cellular schwannoma vs MPNST
Sampling issues
Clinical correlation essential.
Rare Variants:
Melanotic schwannoma
Glandular schwannoma
Microcystic/reticular
Neuroblastoma-like
Epithelioid variant.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Fine needle aspiration from [site], [size] cm encapsulated mass adjacent to [nerve]
Clinical History
[age]/[sex] with [duration] history of slowly growing, mobile mass at [site]. [Neurological symptoms].
Microscopic Examination
Smears show cohesive fascicles of elongated spindle cells with characteristic wavy, buckled nuclei and eosinophilic cytoplasm. Palisading pattern noted. No mitotic activity or cellular atypia.
Immunocytochemistry
S-100: Strongly positive, SOX10: Positive, EMA: Negative, Neurofilament: Negative
Cytological Diagnosis
Cytological features consistent with SCHWANNOMA
Comments
Benign peripheral nerve sheath tumor. Surgical excision with nerve preservation if feasible. Excellent prognosis. Consider genetic counseling if multiple lesions.