Differences in simple morphological variables in ruptured and unruptured middle cerebral artery aneurysms

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Management of unruptured intracranial aneurysms remains controversial in neurosurgery. The contribution of morphological parameters has not been included in the treatment paradigm in a systematic manner or for any particular aneurysm location. The authors present a large sample of middle cerebral artery (MCA) aneurysms that were assessed using morphological variables to determine the parameters associated with aneurysm rupture.


Preoperative CT angiography (CTA) studies were evaluated using Slicer software to generate 3D models of the aneurysms and their surrounding vascular architecture. Morphological parameters examined in each model included 5 variables already defined in the literature (aneurysm size, aspect ratio, aneurysm angle, vessel angle, and size ratio) and 3 novel variables (flow angle, distance to the genu, and parent-daughter angle). Univariate and multivariate statistical analyses were performed to determine statistical significance.


Between 2005 and 2008, 132 MCA aneurysms were treated at a single institution, and CTA studies of 79 aneurysms (40 ruptured and 39 unruptured) were analyzed. Fifty-three aneurysms were excluded because of reoperation (4), associated AVM (2), or lack of preoperative CTA studies (47). Ruptured aneurysms were associated with larger size, greater aspect ratio, larger aneurysm and flow angles, and smaller parent-daughter angle. Multivariate logistic regression revealed that aspect ratio, flow angle, and parent-daughter angle were the strongest factors associated with ruptured aneurysms.


Aspect ratio, flow angle, and parent-daughter angle are more strongly associated with ruptured MCA aneurysms than size. The association of parameters independent of aneurysm morphology with ruptured aneurysms suggests that these parameters may be associated with an increased risk of aneurysm rupture. These factors are readily applied in clinical practice and should be considered in addition to aneurysm size when assessing the risk of aneurysm rupture specific to the MCA location.

Abbreviations used in this paper:CTA = CT angiography; MCA = middle cerebral artery; MIP = maximum intensity projection; MRA = MR angiography; SAH = subarachnoid hemorrhage.

Article Information

Address correspondence to: Rose Du, M.D., Ph.D., Department of Neurosurgery, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts 02115. email: rdu@partners.org.

Please include this information when citing this paper: published online September 7, 2012; DOI: 10.3171/2012.7.JNS111766.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Computed tomography angiograms and 3D models of unruptured and ruptured aneurysms. A and B: Axial (A) and coronal (B) MIP images showing an unruptured right MCA aneurysm. D and E: Axial (D) and coronal (E) MIP images showing a ruptured left MCA aneurysm. C and F: Corresponding 3D reconstructed Slicer images.

  • View in gallery

    Definition of morphological parameters. The parameters measured in 3D models including maximum height, perpendicular height, neck diameter, aneurysm angle, vessel angle, flow angle, and parent-daughter angle. Left: The aspect ratio (AR) is obtained by dividing the perpendicular height by the neck diameter. Right: Calculations of the size ratio (SR). Size ratio = Hmax/Dvcomposite. Dvcomposite is calculated as (Dv1 + Dv2 + Dv3)/3. Dvi = (Dia + Dib)/2, where i = 1, 2, or 3. Dvcomposite is the composite vessel diameter. Dv1, Dv2, and Dv3 represent the individual vessel diameters (mean of 2 locations); D1a, D2a, and D3a represent the vessel diameter at the neck or branching point; and D1b, D2b, D3b represent the vessel diameter 1.5Da away from D1a, D2a, and D3a. The calculations of the size ratio are adapted from Dhar et al.

  • View in gallery

    Scatter plots depicting the interaction between aspect ratio and other morphological parameters.

  • View in gallery

    Scatter plots depicting the interaction between flow angle and other morphological parameters.


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