Stability of infundibular dilatations: a single center follow-up study and systematic review of the literature

PURPOSE: Although infundibular dilatations (IDs) have been thought to be benign anatomical variants, case reports suggest that they can grow and rupture. The aim of this study was to determine whether IDs have a tendency to grow or rupture. METHODS: The study population was collected from the Tampere University Hospital (TAUH) Aneurysm Database. The presence of IDs was screened from the medical records and imaging studies of 356 intracranial aneurysm patients left to follow-up from 2005 to 2020. The imaging studies were reviewed to confirm the IDs, and their clinical course. Finally, we performed a systematic review of published cases of ID leading to aneurysmatic rupture from PubMed. RESULTS: We found 97 typical IDs in 83 patients and 9 preaneurysmal lesions resembling ID in 9 patients. Out of the typical cone-shaped IDs, none grew or ruptured in a total follow-up of 409 patient-years. One preaneurysmal lesion ruptured during a follow-up: this lesion had components of both infundibular dilatation and aneurysm at the beginning of follow-up. In the systematic literature search, we found 20 cases of aneurysmatic SAHs originating from an ID. Of those, only 7 had imaging available prerupture. All 7 IDs were typically cone-shaped, but a branching vessel originating from the apex of ID was only seen in 4/7. CONCLUSION: Typical infundibular dilatations seem to be benign anatomical variants that are stable and, thus, do not need prophylactic treatment or imaging follow-up. Likely, the SAHs reported from IDs were actually caused by misdiagnosed preaneurysmal lesions.