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Background The literature on multiple intracranial aneurysms (MIA) in patients with aneurysmal subarachnoid hemorrhage (aSAH) focuses largely on risk factor analysis and consists essentially of retrospective cohort studies of limited sample size, or studies in populations outside Europe and North America. The purpose of this cohort study was to identify predictors for aneurysm multiplicity and to investigate the anatomic distribution of MIA in a representative Western cohort of patients with aSAH. Methods The Swiss Study of Subarachnoid Hemorrhage (SOS) database includes anonymized data from all tertiary neurovascular facilities in Switzerland. The dataset for 2009–2014 was used to compare characteristics of patients with aSAH and MIA and those with a single intracranial aneurysm (SIA) by means of descriptive and multivariate regression analysis. Results Among 1689 unselected patients with aSAH, 467 had MIA (prevalence, 27.6%). The location of the ruptured index aneurysm was correlated with the probability of finding bystander aneurysms and predicted their likely anatomic distribution. Patients with a ruptured basilar artery aneurysm (odds ratio [OR], 2.11; 95% confidence interval [CI], 1.30–3.44) or a ruptured middle cerebral artery aneurysm (OR, 1.86; 95% CI, 1.35–2.55) were at the greatest risk for having MIA. Larger size of the index aneurysm (OR per 1 mm, 1.03; 95% CI, 1.01–1.06) was also positively correlated with aneurysm multiplicity. Males were less likely than females to have MIA (OR, 0.79; 95% CI, 0.61–1.01). Conclusions In patients with aSAH, the location of the ruptured index aneurysm is correlated with the probability of finding bystander aneurysms, and is predictive of the sites at which bystander aneurysms are most likely to be found.

Objective To analyze the impact of intraoperative ultra-low-field magnetic resonance imaging (MRI) on the extent of tumor resection in nonfunctioning pituitary adenomas (NFPAs). Methods Retrospective analysis was performed of 104 consecutive cases undergoing intraoperative MRI–guided transsphenoidal surgery for NFPA. General patient data; endocrinologic parameters; neurologic examinations; preoperative and postoperative symptoms; preoperative, intraoperative, and postoperative imaging; and proliferation index were evaluated with an overall mean follow-up of 34 months. Results The use of intraoperative MRI led to an increase of the overall remission rate by 52.2%, from 44.2% to 67.3%. Tumor characteristics such as size and invasiveness had an important impact on postoperative remission rate. In patients with macroadenoma and without previous pituitary surgery, a remission rate of 82.2% was achieved. Overall, the sensitivity of intraoperative MRI in the study was 32.4%. There were no false-positive interpretations. A higher proliferation index was found in the 15 patients with postoperative enlargement of residual adenomas or tumor recurrence compared with the other patients of the study group. Conclusions This study shows that the outcome of surgical treatment of NFPAs was improved by the use of intraoperative MRI owing to more radical resection. The remission rate seems to depend on tumor characteristics. Recurrent disease might be reduced by the use of intraoperative MRI leading to more complete surgical resection of NFPAs.