• Benedikt Bandhauer, Philipp Gruber, Lukas Andereggen, Jatta Berberat, Stefan Wanderer, Marco Cattaneo, Gerrit A Schubert, Luca Remonda, Serge Marbacher, and Basil E Grüter.
• 1Department of Neurosurgery, Cantonal Hospital Aarau, Switzerland.
• J. Neurosurg. 2024 Sep 27: 171-7.

ObjectiveIndication for treatment of unruptured intracranial aneurysms (UIAs) is based on several factors, such as patient age, previous medical history, and UIA location and size. For patients harboring UIAs initially managed noninvasively, the treatment strategy during follow-up (FU) can be changed to include surgical or endovascular intervention. This study aims to identify characteristic patterns and potential predictors of UIAs that require revision of the initial management strategy.MethodsThe authors identified intracranial aneurysm (IA) cases newly diagnosed between 2006 and 2022 and initially assigned conservative management. These cases were retrospectively reviewed for 1) patient and UIA characteristics at the time of diagnosis (patient age, comorbidities, previous medical history, potential risk factors, as well as UIA angioarchitecture, location, and size), and 2) any changes in treatment strategy (reason for change, time until intervention, modality of intervention).ResultsAmong 1041 IA cases diagnosed in the study period, 144 were initially assigned conservative management. In 10 (6.9%) of these 144 cases, the treatment indication was modified to microsurgical clipping (n = 6) or endovascular embolization (n = 4) after a median FU of 26 months (IQR 8.5-64.5 months). In these 10 cases, the indication for intervention was attributable to IA growth (n = 7), a change in IA configuration (n = 2), or both (n = 1). Exploratory analyses of the effects of UIA size on diagnosis in terms of the hazard for a change of decision suggested an effect starting from 3 mm. No conservatively managed UIAs (n = 144) ruptured during the study period (median FU 24.5 months, IQR 7.75-55.75 months).ConclusionsThe likelihood of a shift to invasive UIA treatment is relatively low if a conservative therapeutic strategy was initially established. However, for cases with changes to the treatment strategy, the change is most often attributable to UIA growth over time. UIAs measuring < 3 mm at initial diagnosis are less likely to be later treated interventionally than those > 3 mm at diagnosis. Therefore, conservatively managed patients with UIAs should be closely monitored with regular radiographic FUs, particularly if the UIA measured > 3 mm at the time of diagnosis.

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