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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 C; 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. chi2 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.
Sadatomo et al. (Sat,) studied this question.