Novel Morphological Classification of Intracranial Aneurysm Wall Irregularity Associates Specific Features with Increased Size and Rupture Risk: A Retrospective Single-Center Cross-Sectional Study

Introduction/Objectives: Wall irregularity is a known risk factor in the evaluation of intracranial aneurysms, but the prognostic value of its subtypes remains unclear. Materials and methods: In this retrospective single-center cross-sectional study (2023–2025), we reviewed consecutive adult patients with intracranial aneurysms. Morphology was classified as daughter sac, multilobulated, or complex irregularity. We compared rupture status and calculated PHASES, ELAPSS, and UIATS scores. Principal Component Analysis (PCA), and logistic and linear regression were applied. Results: A total of 180 patients with 180 index aneurysms were included; mean age was 67.2 ± 12.1 years, and 72.2% were women. Overall, 43.3% of aneurysms were irregular, specifically: daughter sac (25.0%), multilobulated (36.1%), and complex irregularity (11.1%). SAH occurred in 40 patients (22.2%). Ruptured aneurysms had larger maximum diameter, size ratio, and aspect ratio (all p < 0.0001), plus higher 5-year PHASES (p = 0.0091) and ELAPSS growth scores (p < 0.0001). PCA identified three clusters with differing 5-year rupture risks; Cluster 3 had the highest risk (5.71 ± 5.25%) and was characterized by a higher proportion of daughter sac and multilobulated morphology (p = 1.65 × 10−7 and 8.80 × 10−16). Linear models showed each irregular subtype was associated with significantly larger aneurysm size. Conclusions: Irregular wall patterns were common and associated with larger aneurysm dimensions and higher risk scores. These findings support further investigation of refined morphological descriptors in rupture risk stratification.