title: Parasellar arachnoid cyst presenting with a nonpupil sparing third nerve palsy mimicking a posterior communicating artery aneurysm in an adult.
abstract: BACKGROUND
  Arachnoid cysts are congenital lesions that contain fluid identical to cerebrospinal fluid (CSF). They usually do not communicate with CSF spaces. The vast majority of arachnoid cysts are congenital asymptomatic lesions that are discovered incidentally. Those lesions that do become symptomatic typically present in childhood with signs and symptoms of intracranial hypertension, seizures, and focal neurologic deficits specific to cyst location.
  
  
  METHODS
  A rare case of a parasellar arachnoid cyst presenting with oculomotor palsy is presented. The patient is a 45-year-old male who presented with acute onset diplopia and frontal headache. Neurologic examination revealed right ptosis, pupillary dilation, and opthalmoparesis consistent with an oculomotor palsy. Computed tomography (CT) scan and lumbar puncture failed to reveal evidence of a subarachnoid hemorrhage. Magnetic resonance imaging (MRI) of the brain demonstrated a 1 cm right parasellar nonenhancing mass that was hyperintense on T2 flair and with a fluid-fluid level concerning for a thrombosed posterior communicating artery (PCommA) aneurysm. There was an additional finding of a left occipital pole intraparenchymal hemorrhage in the setting of multiple hereditary cavernomas. Formal cerebral angiography revealed normal intracranial and extracranial vasculature. The patient was taken to the operating room for a right frontotemporal craniotomy, which revealed compression of the right oculomotor nerve by an arachnoid cyst. The cyst was fenestrated and resected with decompression of the oculomotor nerve. Postoperatively, the third nerve palsy had completely resolved.
  
  
  CONCLUSIONS
  The above case demonstrates that arachnoid cysts should be considered in the differential for patients presenting with nonpupil sparing third nerve palsy and require timely surgical intervention. As is the case for an expanding PCommA aneurysm, prompt decompression results in the best chance for recovery of oculomotor nerve function.
authors: Department of Neurological Surgery, UPMC Presbyterian Hospital, M8709 South Tower, 200 Lothrop Street, Pittsburgh, PA 15213, USA.
authors: Zachary J
authors: ZJ
authors: Tempel
authors: Stephen A
authors: SA
authors: Johnson
authors: Paul S
authors: PS
authors: Richard
authors: Robert M
authors: RM
authors: Friedlander
authors: William E
authors: WE
authors: Rothfus
authors: Ronald L
authors: RL
authors: Hamilton
keywords: Arachnoid cyst; cavernoma; oculomotor palsy
references: Surg Neurol. 1995 Jan;43(1):31-3; discussion 34
references: 7701419
references: J Neurosurg. 1972 May;36(5):548-51
references: 5026541
references: Indian J Pediatr. 2007 Nov;74(11):1034-6
references: 18057687
references: Ann Neurol. 1983 Dec;14(6):696-7
references: 6651257
references: J Neuroophthalmol. 2008 Sep;28(3):192-7
references: 18769282
references: Neurosurgery. 1986 Sep;19(3):454-7
references: 3762897
references: J AAPOS. 2009 Jun;13(3):308-9
references: 19541275
references: Neurosurgery. 1981 Jul;9(1):70-5
references: 7279177
references: J Neurosurg. 2005 Nov;103(5 Suppl):454-7
references: 16302620
references: J Neuropathol Exp Neurol. 1981 Jan;40(1):61-83
references: 7205328