Orbital Tumors - Schwannomas

Description of Orbital Schwannomas

  • Schwannomas are slow-growing, benign tumours that develop within {the} outer covering of peripheral and sympathetic nerves formed by Schwann cells, called {the} nerve sheath. They are may also be called neurilemmomas and often involve sensory and motor nerves supplying {the} orbital region. Schwannomas are rare tumours and constitute about 1% of all orbital tumours and 35% of peripheral nerve tumours within {the} orbit. It has a
  • It primarily affects individuals between 20 and 60 years old, with 10-15% cases accompanied by neurofibromatosis.

Pathophysiology of Orbital Schwannomas

  • Orbital schwannomas are seen as encapsulated growths within a peripheral or sympathetic nerve, which distinguishes them from a neurofibroma that affect nerve fibres themselves. They are benign tumours and are rarely associated with malignant transformation. They usually occur in {the} superior temporal region or muscle cone of {the} orbit pushing {the} eyeball forward and downward.
  • The orbital schwannomas has {the} following histologic components that help in a pathologic diagnosis:
    • Antoni A type areas: Constitute solid areas of tumour cells forming {the} bulk of {the} tumour.
    • Antoni B type areas: Contains loose cystic spaces with no axons.
    • Verocay body: Represents palisading of {the} tumour nuclei in acellular zones of {the} tumour.
  • Verocay bodies, when present, are a useful marker for orbital schwannoma. Histochemical staining with S-100 might possibly be positive.

Symptoms and Signs of Orbital Schwannomas

  • A patient with orbital schwannoma usually presents with a slowly progressive painless bulging of {the} eyeball, proptosis and takes years or even decades to produce symptoms.
  • Other symptoms and signs commonly seen are:
    • Oedema of {the} eyelids
    • Dystopia of {the} eyeball
    • Exophthalmos
    • Impaired ocular motility
    • Disturbances in vision including visual loss
    • Changes in {the} optic disc such as choroidal striae with hyperopia

Diagnosis of Orbital Schwannomas

  • Clinical history of a slow-growing tumour within {the} orbit producing symptoms hinting to a diagnosis of orbital schwannoma. This suspicion is further supported by {the} presence of an encapsulated mass.
  • Diagnosis is confirmed by Computed Tomography and Magnetic Resonance Imaging of {the} orbital region. Histologic diagnosis is obtained after surgical excision of {the} tumour and shows Antoni A or Antoni B areas, Verocay bodies and positive for S-100 immunohistological stain.

Treatment of Orbital Schwannomas

  • Complete surgical excision is {the} treatment of choice for orbital schwannoma. Being well-encapsulated, it is easily removed. There is however a small risk of recurrence. The risk of malignant transformation is minimal.
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