Pearls & Oy-sters: Trigeminal Cystic Schwannoma Presenting With Foster Kennedy Syndrome, Sixth Nerve Palsy, and Focal Seizures

Foster Kennedy syndrome refers to a finding of optic atrophy in one eye from direct compression of the optic nerve by a mass lesion and contralateral papilledema in the non-atrophic optic nerve caused by increased intracranial pressure. When the fundoscopy finding is not due to a direct compressive mass, the term pseudo-Foster Kennedy syndrome is used; this can be caused by any process or processes that result in optic atrophy in one eye and optic disc edema in the other. Identifying Foster Kennedy syndrome in a patient calls for expedient neuroimaging looking for an intracranial mass lesion. In this paper, we present a case of a patient presenting with vision loss and Foster Kennedy syndrome who was found to have a large trigeminal cystic schwannoma. While several other accompanying symptoms were not evident from the patient complaint, careful history and physical examination revealed additional localizing clues: unilateral sensory changes in the face and pterygoid and masseter atrophy, unilateral cranial nerve VI palsy, and episodes of intense déjà vu sensation which were presumed to represent temporal lobe onset focal aware seizures. Trigeminal schwannomas are a rare entity, and they are even more rarely cystic. This case highlights an unusual scenario where slow expansion of the tumor ultimately resulted in vision loss and presentation of the patient to medical attention. To our knowledge, this is the first report of a trigeminal schwannoma causing Foster Kennedy syndrome.