Intraoperative premature rupture of middle cerebral artery aneurysms: risk factors and sphenoid ridge proximation sign.

OBJECTIVE This study was an investigation of surgical cases of a ruptured middle cerebral artery (MCA) aneurysm that was conducted to identify the risk factors of an intraoperative premature rupture. METHODS Among 927 patients with a ruptured intracranial aneurysm who were treated over an 8-year period, the medical records of 182 consecutive patients with a ruptured MCA aneurysm were examined for cases of a premature rupture, and the risk factors were then investigated. The risk factors considered for an intraoperative premature rupture of an MCA aneurysm included the following: patient age; sex; World Federation of Neurosurgical Societies clinical grade; modified Fisher grade; presence of an intracerebral hemorrhage (ICH); location of the ICH (frontal or temporal); volume of the ICH; maximum diameter of the ruptured MCA aneurysm; length of the preaneurysmal M segment between the carotid bifurcation and the MCA aneurysm; and a sign of sphenoid ridge proximation. The sphenoid ridge proximation sign was defined as a spatial proximation < 4 mm between the sphenoid ridge and the rupture point of the MCA aneurysm, such as a daughter sac, irregularity, or dome of the aneurysm, based on the axial source images of the brain CT angiography sequences. RESULTS A total of 11 patients (6.0%) suffered a premature rupture of the MCA aneurysm during surgery. The premature rupture occurrences were classified according to the stage of the surgery, as follows: 1) craniotomy and dural opening (n = 1); 2) aspiration or removal of the ICH (n = 1); 3) retraction of the frontal lobe (n = 1); 4) dissection of the sphenoid segment of the sylvian fissure to access the proximal vessel (n = 4); and 5) perianeurysmal dissection (n = 4). The multivariate analysis with a binary logistic regression revealed that presence of a sphenoid ridge proximation sign (p < 0.001), presence of a frontal ICH associated with the ruptured MCA aneurysm (p = 0.019), and a short preaneurysmal M segment (p = 0.043) were all statistically significant risk factors for a premature rupture. Plus, a receiver operating characteristic curve analysis revealed that a preaneurysmal M segment length ≤ 13.3 mm was the best cutoff value for predicting the occurrence of a premature rupture (area under curve 0.747; sensitivity 63.64%; specificity 81.66%). CONCLUSIONS Patients exhibiting a sphenoid ridge proximation sign, the presence of a frontal ICH, and/or a short preaneurysmal M segment are at high risk for an intraoperative premature rupture of a MCA aneurysm. Such high-risk MCA aneurysms have a superficial location close to the arachnoid in the sphenoidal compartment of the sylvian fissure and have a rupture point directed anteriorly.