title: Evaluation of an anatomic definition of non-aneurysmal perimesencephalic subarachnhoid hemorrhage.
abstract: OBJECTIVE
  Perimesencephalic subarachnoid hemorrhage (PSAH) is not consistently defined in the existing literature. The purpose of this study was to test the inter-observer variability and specificity for non-aneurysmal subarachnoid hemorrhage (SAH) of an anatomic definition of PSAH.
  
  
  METHODS
  Medical records of all patients who underwent catheter angiography for evaluation of non-traumatic SAH between July 2002 and April 2012 were reviewed. Patients with anterior circulation aneurysms were excluded. Three blinded reviewers assessed whether each admission CT scan met the following anatomic criteria for PSAH: (1) center of bleeding located immediately anterior and in contact with the brainstem in the prepontine, interpeduncular, or posterior suprasellar cistern; (2) blood limited to the prepontine, interpeduncular, suprasellar, crural, ambient, and/or quadrigeminal cisterns and/or cisterna magna; (3) no extension of blood into the Sylvian or interhemispheric fissures; (4) intraventricular blood limited to incomplete filling of the fourth ventricle and occipital horns of the lateral ventricles (ie, consistent with reflux); (5) no intraparenchymal blood.
  
  
  RESULTS
  56 patients with non-aneurysmal SAH and 50 patients with posterior circulation or posterior communicating artery aneurysms were identified. Seventeen (16%) of the 106 admission CT scans met the anatomic criteria for PSAH. No aneurysm was identified in this subgroup. Inter-observer agreement was excellent with κ scores of 0.89-0.96 and disagreement in 2.8% (3/106) of cases.
  
  
  CONCLUSIONS
  Our anatomic definition of PSAH correlated with a low risk of brain aneurysm and was applied with excellent inter-observer agreement.
authors: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Missouri, USA.
authors: Adam N
authors: AN
authors: Wallace
authors: Washington University School of Medicine, St Louis, Missouri, USA.
authors: Ross
authors: R
authors: Vyhmeister
authors: Department of Radiology, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
authors: Jeffrey N
authors: JN
authors: Dines
authors: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Missouri, USA.
authors: Arindam R
authors: AR
authors: Chatterjee
authors: Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Missouri, USA.
authors: Akash P
authors: AP
authors: Kansagra
authors: Sharp Grossmont Hospital, La Mesa, California, USA.
authors: Ryan
authors: R
authors: Viets
authors: Texas Radiology Associates, Plano, Texas, USA.
authors: Justin T
authors: JT
authors: Whisenant
authors: Mallinckrodt Institute of Radiology and Department of Neurological Surgery, Washington University, St Louis, Missouri, USA.
authors: Christopher J
authors: CJ
authors: Moran
authors: Mallinckrodt Institute of Radiology and Department of Neurological Surgery, Washington University, St Louis, Missouri, USA.
authors: DeWitte T
authors: DT
authors: Cross
authors: Mallinckrodt Institute of Radiology, Departments of Neurological Surgery and Neurology, Washington University School of Medicine, St Louis, Missouri, USA.
authors: Colin P
authors: CP
authors: Derdeyn
mesh_terms: D000328:Adult; D000368:Aged; D006801:Humans; D008636:Mesencephalon / Q000000981:diagnostic imaging*; D008875:Middle Aged; D016037:Single-Blind Method; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000592:standards*
keywords: Aneurysm; Angiography; CT; Hemorrhage; Stroke