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Differences in the Basilar Artery Bifurcation Angle Among Patients Who Present With a Ruptured Aneurysm at the Top of the Basilar Artery and Patients With Perimesencephalic Subarachnoid Hemorrhage: A Retrospective Cross-sectional Study

Jagadeesan, Bharathi D. MD*,‡; Kadkhodayan, Yasha MD§; Delgado Almandoz, Josser E. MD§; Wallace, Adam MD; Cross, Dewitte T. III MD¶,‖; Derdeyn, Colin P. MD¶,‖,#; Zipfel, Gregory J. MD‖,#; Dacey, Ralph G. Jr MD; Moran, Christopher J. MD¶,‖

doi: 10.1227/01.neu.0000429837.45820.9c
Research-Human-Clinical Studies

BACKGROUND: The angle of the basilar artery bifurcation of (BAB angle) is thought to influence the risk of the development and rupture of aneurysms at this site. It is, however, unknown whether the BAB angle also influences the incidence of angiographically negative perimesencephalic subarachnoid hemorrhage (PMSAH).

OBJECTIVE: We performed a retrospective cross-sectional study comparing the BAB angle in a series of patients who presented with subarachnoid hemorrhage from a ruptured aneurysm at the top of the basilar artery (BSAH) with the BAB angle in a series of patients who presented with PMSAH.

METHODS: Consecutive patients who presented to our institution with PMSAH or BSAH between January 1, 2005 and December 31, 2010 were studied. Patients with PMSAH were further subdivided into patients with classic PMSAH (CPMSAH) and those with nonclassic PMSAH (NCPMSAH) based on initial head computed tomography examinations. In each patient, the BAB angle was measured on the standard cranial anteroposterior projections after vertebral artery injections.

RESULTS: A total of 21 patients with CPMSAH, 30 patients with NCPMSAH, and 31 patients with BSAH were studied. The BAB angle was significantly smaller in patients with CPMSAH (87.7 ± 17.1 degrees) and NCPMSAH (98.4 ± 21.1 degrees) compared with patients with BSAH (135.0 ± 30.8 degrees) (P < .001).

CONCLUSION: The significantly lower BAB angle in PMSAH patients compared with BSAH patients suggests that bleeding in PMSAH is either nonarterial in nature or is secondary to variations in hemodynamic arterial stress at the top of the basilar artery that need to be studied further with computational models.

ABBREVIATIONS: BAB, basilar artery bifurcation

BAB angle, angle of the basilar artery bifurcation

BSAH, aneurysm at the top of the basilar artery

CPMSAH, classic perimesencephalic subarachnoid hemorrhage

CTA, computed tomography angiography

DSA, digital subtraction angiography

NCPMSAH, nonclassic perimesencephalic subarachnoid hemorrhage

PCA, posterior cerebral artery

PMSAH, perimesencephalic subarachnoid hemorrhage

SAH, subarachnoid hemorrhage

Departments of *Radiology and

Neurosurgery, University of Minnesota, Minneapolis, Minnesota;

§Department of Interventional Neuroradiology, Abbot Northwestern Hospital, Minneapolis, Minnesota;

Departments of Radiology,

Neurological Surgery, and

#Neurology, Washington University School of Medicine, St. Louis, Missouri

Correspondence: Bharathi D. Jagadeesan, MD, MMC 292, Mayo Memorial Building, 420 Delaware Street SE, Minneapolis, MN 55455. E-mail:

Received September 5, 2012

Accepted March 8, 2013

Copyright © by the Congress of Neurological Surgeons