Occipital petalia as a predictive imaging sign for transverse sinus dominance

Occipital petalia is an anatomic description where one of the occipital lobes protrudes towards the contralateral side. Transverse sinus (TS) asymmetry might cause diagnostic challenges with regards to thrombotic or compressive pathologies involving these sinuses. In this study, we investigated the association between occipital petalia and TS hypoplasia on MRI studies.

In 264 subjects with no neurological complaints, occipital bending was determined on T1-weighted images based on the angulation of interhemispheric fissure between occipital lobes with respect to an imaginary midline. TS asymmetry was evaluated visually. Information on handedness and ocular dominance was also gathered from all participants.

Rightwards bending was observed in 72 subjects (27%), whereas leftwards bending was present in only 10 participants (4%). The presence or direction of bending was related neither to hand nor ocular dominance. In participants with rightwards bending, 72% had a larger TS on the right-side, while only a single subject had a left-sided predilection for venous drainage. In subjects with leftwards bending, 70% had a left-dominant TS drainage system and none had a larger TS on the right. Overall, the direction of bending was predictive of TS dominance on the ipsilateral side with a PPV of 72% (95%CI, 60-82%) for right and 70% (95%CI, 35-92%) for left.

The direction of bending, a relatively straightforward radiologic diagnosis, is closely linked to the side of TS hypoplasia, and thereby might provide physicians with an additional diagnostic clue regarding the interpretation of imaging findings related to TSs and their pathologies.