Introduction
Schwannomas (also known as neuromas, neurinomas “of Verocay” and neurilemmomas) are benign, slow-growing encapsulated nerve sheath tumours found most commonly in the extremities and head and neck region.
- M/C nerve sheath tumor (89% cases)
Aetiology
Sporadic occurrence:
90% cases
Syndromic association:
- Neurofibromatosis type 2 (NF2) “Von Recklinghausen’s disease” (5-18% cases)
- Schwannomatosis
- Carney complex (2%)
- Meningiomatosis with/without NF2 (5%)
Pathophysiology
Schwann cells (derived from the neural crest)
- Schwannomas may occur in any organ or nerve trunk, with the exception of cranial nerves I and II, which lack Schwann cells.
Location:
Tumors are generally located in the upper limbs, followed by the head, the trunk, and flexor surfaces of the lower extremities.
- Vestibular schwannomas (60% cases)
- Spinal schwannomas
Histopathology:
- Classic schwannoma: Encapsulated tumor with two distinct histological regions:
- Antoni A tissue: Hypercellular spindle cells, sometimes palisade around eosinophilic areas (Verocay bodies)
- Antoni B tissue: Hypocellular myxomatous pattern with a background of loose connective tissue. Cyst, hemorrhage, and fatty degeneration may be present.
- Cellular schwannoma (uncommon): Compact hypercellular areas composed entirely of Antoni A areas and devoid of Verocay bodies.
- Plexiform schwannoma: Plexiform pattern of growth involving multiple fascicles having an Antoni A pattern
- Melanotic schwannoma: Rare, potentially malignant neoplasm that presents with epithelioid cells and melanin accumulated in neoplastic cells and melanophages
Clinical features
Schwannomas grow slowly and may exist for years without any symptom manifestation. Symptoms produced are due to organ displacement or pressure effects on surrounding structures.
Clinical types:
Schwannomas can present in various locations, which explains the variations in clinical presentations. Tenderness is felt when palpating the mass. Neurologic symptoms may show if the tumor is large.
- Schwannomas in the extremities: Asymptomatic mass, mild pain in the area, or paresthesia due to pressure on the parent nerve
- Sciatic nerve schwannomas: Mimic disk herniation with low back pain with radiation down the leg
- C7 nerve root schwannoma: Thoracic outlet syndrome
- Ankle/wrist schwannoma: Tarsal tunnel syndrome or carpal tunnel syndrome
- Vestibular schwannomas: Decreased hearing, tinnitus, and imbalance
- Trigeminal schwannoma: Numbness/pain in trigeminal nerve distribution
Diagnosis
Magnetic resonance imaging (MRI):
- Oval/round mass with isointense/hypointense signal on T1-weighted images
- Hyperintense, heterogeneous signal on T2-weighted images
- Lesion enhances uniformly with gadolinium contrast
- Target sign (central area of hypointensity with a peripheral T2 signal hyperintensity): M/specific sign of a peripheral nerve sheath tumor but not specific for schwannoma.
Tissue biopsy:
Management
Complete surgical resection with partial/complete resection of viscera (to attain negative margin)
Treatment of choice
