title: De Novo Intraneural Arachnoid Cyst Presenting with Complete Third Nerve Palsy: Case Report and Literature Review.
abstract: BACKGROUND
  Intraneural arachnoid cyst is an extremely rare etiology of isolated cranial nerve palsy. Although seldom encountered in clinical practice, this pathology is amenable to surgical intervention. Correct identification and treatment of the cyst are required to prevent permanent nerve damage and potentially reverse the deficits. We describe a rare case of isolated third nerve palsy caused by an intraneural arachnoid cyst.
  
  
  METHODS
  A 49-year-old woman with a recent history of headaches experienced acute onset of painless left-sided third nerve palsy. According to hospital records ptosis, mydriasis, absence of adduction, elevation, and intorsion were noted in the left eye. Computed tomography and magnetic resonance imaging studies showed an extra-axial, 1-cm lesion along the left paraclinoid region, causing mild indentation on the uncus. There was dense fluid layering dependently concerning for hemorrhage, but no evidence of aneurysms. A pterional craniotomy was performed, revealing a completely intraneural arachnoid cyst in the third nerve. The cyst was successfully fenestrated. At 7-month follow-up, the left eye had recovered intact intorsion and some adduction, but the left pupil remained dilated and nonreactive. There was still no elevation and no afferent pupillary defect. Double vision persisted with partial improvement in the ptosis, opening up to more than 75% early in the day.
  
  
  CONCLUSIONS
  To our knowledge, this is the first report of an intraneural arachnoid cyst causing isolated third nerve palsy. This rare pathology proves to be both a diagnostic and therapeutic challenge.
authors.affiliation: Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Danielle
authors.initials: D
authors.lastname: Brewington
authors.affiliation: Department of Neurosurgery, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA. Electronic address: dmitriy.n.petrov@gmail.com.
authors.forename: Dmitriy
authors.initials: D
authors.lastname: Petrov
authors.affiliation: Department of Neurosurgery, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Whitmore
authors.affiliation: Division of Neuro-ophthalmology, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA.
authors.forename: Grant
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Radiology, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA.
authors.forename: Ronald
authors.initials: R
authors.lastname: Wolf
authors.affiliation: Department of Neurosurgery, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA.
authors.forename: Eric L
authors.initials: EL
authors.lastname: Zager
mesh_terms: D016080:Arachnoid Cysts / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery; D000072226:Computed Tomography Angiography; D003399:Craniotomy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D015840:Oculomotor Nerve Diseases / Q000150:complications* / Q000000981:diagnostic imaging / Q000601:surgery; D015898:Tomography Scanners, X-Ray Computed
keywords: Arachnoid cyst; Cyst; Third nerve palsy