CTA Evaluation of Basilar Septations: An Entity Better Characterized as Aberrant Basilar Fenestrations

A basilar artery intraluminal septation is an exceedingly rarely reported, presumed congenital abnormality. In our clinical practice, we have occasionally noticed an intraluminal band within the inferior aspect of the basilar artery on CTA. Furthermore, we have noticed, at times, the presence of a punctate calcification associated with this finding. We hypothesized that what previous studies have called "basilar septations" in fact represent miniature and thus aberrant basilar fenestrations.

We retrospectively reviewed CTA studies obtained between January 1, 2017, and August 31, 2019. Identified intraluminal basilar abnormalities were classified as either basilar septations or basilar fenestrations. Association with other posterior circulation abnormalities was documented.

A total of 3509 studies were examined. A basilar intraluminal abnormality was evident in 80 patients (2.3%). Of these 80 patients, 59 were classified as having a basilar fenestration (1.7%) and 21 were classified as having basilar septations (0.6%). Associated calcification was evident in 3 of the basilar fenestration cases and 13 of the basilar septation cases.

Basilar septations most likely represent and should be referred to as aberrant basilar fenestrations. They should be interpreted as benign congenital incidental findings and should not be misinterpreted as focal dissections or arterial webs. Important variations in the morphology of aberrant basilar fenestrations exist, including areas of thinning, varying thickness, and nodularity. Therefore, when associated with calcification or nodularity, aberrant basilar fenestrations should not be confused with focal intraluminal thrombi or calcified or noncalcified emboli.