Morphological differences between ruptured and unruptured cases in middle cerebral artery aneurysms

OBJECTIVE: To elucidate the morphological differences between ruptured and unruptured aneurysms, three-dimensional digital subtraction angiography was performed in 44 cases (20 unruptured, 24 ruptured) of middle cerebral artery aneurysm. METHODS: When the neck was located on the extension of the midline of the parent artery, it was defined as Type Q when it was not, it was defined as Type D. Aspect ratio (AP ratio; dome/neck ratio) and daughter artery ratio (DA ratio; diameter of the larger daughter artery/diameter of the smaller daughter artery) were calculated, and these ratios were compared for ruptured and unruptured cases. RESULTS: Nineteen cases were Type C and 25 cases were Type D. chi(2) test revealed that there were significantly more ruptured cases among Type C (14 out of 19) compared with Type D (10 out of 25) (P < 0.05). AP ratios were 2.24 +/- 0.75 for ruptured cases and 1.56 +/- 0.58 for unruptured cases. DA ratios were 1.53 +/- 0.54 in ruptured cases and 2.14 +/- 0.80 for unruptured cases. Both showed significant differences (P < 0.01). In cases with an AP ratio of 1.8 or greater and a DA ratio less than 1.7, 13 out of 15 (87%) were ruptured cases. On the contrary, in cases with an AP ratio less than 1.8 and a DA ratio of 1.7 or greater, 12 out of 13 (92%) were unruptured cases. CONCLUSION: Type C and equality of the diameters of two daughter arteries, together with high AP ratios, seem to be morphological factors that associate with aneurysmal rupture.