Clinico-radiological features of optic nerve sheath schwannoma: Review and illustrative case.

The optic nerve sheath is a rare site for schwannoma, to our knowledge 19 optic nerve sheath schwannoma (ONSS) cases have been reported. Difficulty can arise in diagnosis as imaging findings can be relatively non-specific. We describe a case of ONSS that mimicked orbital cavernous venous malformation pre-operatively. A 43-year-old woman presented with right subacute visual loss, reduced vision to 6/48 and signs of optic neuropathy. Endocapsular excision of the mass, which was adherent to the optic nerve, was accomplished from an endoscopic endonasal approach utilizing a 5-hand technique of retrocaruncular dissection. Histology showed spindle-shaped tumour cells with S100 positivity, consistent with ONSS. At 6 months post-operatively vision had improved to 6/6. We show that an endoscopic endonasal approach, augmented by transcaruncular retraction, can be utilized to excise ONSS with an excellent outcome. We review published cases of ONSS, including demographic and clinical features, differential diagnosis based on radiological features, and described outcomes, which are generally poor.