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Schwannoma

Schwannomas (also known as neuromas, neurinomas “of Verocay” and neurilemmomas) are benign, well-encapsulated, slow-growing nerve sheath tumors composed exclusively of Schwann cells derived from the neural crest.

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
Very high magnification micrograph of a schwannoma. HPS stain. A cellular Antoni A area is seen on the right of the image. A paucicellular Antoni B area is seen on the left of the image. | Nephron – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17748282

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.
Sagittal STIR MRI image of the head and neck ( A ) reveals a well-defined hyperintense mass (red arrow) within the base of the tongue. A coronal postcontrast fat-saturated image ( B ) shows heterogeneous enhancement of the lesion abutting the right submandibular gland. | Badar Z, Farooq Z, Zaccarini D, Ezhapilli S R. Tongue base schwannoma: differential diagnosis and imaging features with a case presentation. Radiol Case Rep. 2016;11(04):336–340.

Tissue biopsy:

Schwannoma of the tongue is composed of spindled cells with hypocellular and hypercellular regions in addition to focal nuclear-palisading areas (Verocay bodies). | Badar Z, Farooq Z, Zaccarini D, Ezhapilli S R. Tongue base schwannoma: differential diagnosis and imaging features with a case presentation. Radiol Case Rep. 2016;11(04):336–340.

Management

Complete surgical resection with partial/complete resection of viscera (to attain negative margin)

Treatment of choice
Case 1. A) Axial T2-weighted image demonstrating a fusiform isogenous mass. B) Intraoperative finding of the well-circumscribed, encapsulated and solid mass along the medial plantar nerve | Angelini, A., Bevoni, R., Biz, C., Cerchiaro, M. C., Girolami, M., & Ruggieri, P. (2019). Schwannoma of the foot: report of four cases and literature review. Acta bio-medica : Atenei Parmensis, 90(1-S), 214–220. https://doi.org/10.23750/abm.v90i1-S.8079

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