title: Perimesencephalic hemorrhage. Exclusion of vertebrobasilar aneurysms with CT angiography.
abstract: OBJECTIVE
  It is important to recognize a perimesencephalic pattern of hemorrhage in patients with subarachnoid hemorrhage (SAH), because in 95% of these patients the cause is nonaneurysmal and the prognosis is excellent. The purpose of this study was to investigate whether CT angiography can accurately exclude vertebrobasilar aneurysms in patients with perimesencephalic patterns of hemorrhage and therefore replace digital subtraction angiography (DSA) in this setting.
  
  
  METHODS
  In 40 patients with posterior fossa SAH as shown on unenhanced CT, 2 radiologists independently evaluated unenhanced CT for distinguishing between perimesencephalic and nonperimesencephalic pattern of hemorrhage and assessed CT angiography for detection of aneurysms. All patients subsequently underwent DSA or autopsy.
  
  
  RESULTS
  Observers agreed in 38 of 40 patients (95%) in differentiating perimesencephalic and nonperimesencephalic patterns of hemorrhage on unenhanced CT. On the CT angiograms, both observers detected a vertebrobasilar aneurysm in 16 patients and no aneurysm in 24 patients. These findings were confirmed by DSA or autopsy. No patients with a perimesencephalic pattern of hemorrhage were found to have an aneurysm on either CT angiography or DSA.
  
  
  CONCLUSIONS
  Good recognition of a perimesencephalic pattern of hemorrhage is possible on unenhanced CT, and CT angiography accurately excludes and detects vertebrobasilar aneurysms. DSA can be withheld in patients with a perimesencephalic pattern of hemorrhage and negative CT angiography.
authors.affiliation: Departments of Radiology, Utrecht University Hospital, Utrecht, The Netherlands.
authors.forename: B K
authors.initials: BK
authors.lastname: Velthuis
authors.forename: G J
authors.initials: GJ
authors.lastname: Rinkel
authors.forename: L M
authors.initials: LM
authors.lastname: Ramos
authors.forename: T D
authors.initials: TD
authors.lastname: Witkamp
authors.forename: M S
authors.initials: MS
authors.lastname: van Leeuwen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015901:Angiography, Digital Subtraction; D001488:Basilar Artery / Q000000981:diagnostic imaging / Q000473:pathology*; D002533:Cerebral Angiography; D002543:Cerebral Hemorrhage / Q000000981:diagnostic imaging* / Q000473:pathology; D002560:Cerebrovascular Circulation; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000473:pathology; D008875:Middle Aged; D014057:Tomography, X-Ray Computed; D014711:Vertebral Artery / Q000000981:diagnostic imaging / Q000473:pathology*