Parasellar arachnoid cyst presenting with a nonpupil sparing third nerve palsy mimicking a posterior communicating artery aneurysm in an adult
The patient is a 45-year-old male with a past medical history significant for multiple hereditary cavernous hemangiomas and Hodgkin’s lymphoma in remission following treatment with chemotherapy and radiation. He presented to his primary care physician with acute onset double vision, frontal headaches, and lid lag of the right eye. On computed tomography (CT) imaging [], he was found to have a left occipital hemorrhage and was transferred to this facility for further work-up and management. On examination in the emergency room, he was found to have right eye ptosis, papillary dilation as well as restriction of leftward and upgaze consistent with a right third nerve palsy. There was no evidence of subarachnoid blood on the CT scan. A lumbar puncture was performed, which was unremarkable. MRI of the brain [] demonstrated a 2 cm left occipital pole hemorrhage and a 1 cm nonenhancing right parasellar mass with a fluid-hematocrit level that was hyperintense on T2 flair imaging without diffusion restriction that appeared to compress the right third cranial nerve []. These findings were concerning for a thrombosed PCommA aneurysm. Subsequent CT angiography of the head/neck and conventional cerebral angiography revealed normal intracranial and extracranial vessels without filling of the right parasellar mass.\nThe patient was taken to the operating room and underwent a right frontotemporal craniotomy. Intraoperatively, a right parasellar cystic lesion resembling an arachnoid cyst was identified, medial to the third nerve, which was pushed laterally []. The cyst was fenestrated and clear fluid was expressed, which appeared grossly similar to CSF. The fluid was easily aspirated, and there was no evidence of hemosiderin deposition in the cyst wall or of blood products within the cyst. This is in contrast to the suggestion of MRI, which raised the possibility of the content being hemorrhagic. The wall of the cyst was then carefully dissected and sent for permanent section analysis, which confirmed the diagnosis of an arachnoid cyst [].\nImmediately following surgery, the third nerve deficit improved but was still present. At his routine 2-week postoperative visit, he had subjective complaints of intermittent diplopia without evidence of a third nerve palsy on neurologic examination. When he presented for his three-month postoperative visit, he was symptom free and neurologically intact. MRI at that time revealed no evidence of a residual or recurrent arachnoid cyst [].