Progressive sixth nerve palsy secondary to intracavernous arachnoid cyst and complicated by contralateral optic nerve sheath meningioma.

INTRODUCTION: Optic nerve sheath meningiomas and intracavernous arachnoid cysts are both fairly rare conditions, and to the best of our knowledge, have not been previously reported to co-occur in the same patient. Both can cause diplopia, but only ONSMs have been documented to demonstrate progressive worsening of ocular motility.

CASE REPORT: A 67-year-old woman with blur and diplopia demonstrated a right optic neuropathy and limited ductions bilaterally. Neuroimaging revealed a right optic nerve sheath meningioma and left intracavernous arachnoid cyst. She was conservatively managed with neurosurgical surveillance for 1.5 years, until her diplopia worsened. Ocular motility re-evaluation demonstrated a worsening left abduction deficit, suggesting interval change of the intracavernous cyst, rather than the meningioma.

CONCLUSION: There are only a few reported cases of cranial nerve VI palsy secondary to a cavernous sinus arachnoid cyst. However, this is the first reported case in a patient with a concurrent optic nerve sheath meningioma, and the first case demonstrating progressive worsening of a sixth cranial nerve palsy from an intracavernous arachnoid cyst. Determining which comorbidity caused worsening of symptoms played a critical role in the management of this patient.