A rare anatomical variant of the relationship between a branch of the superior cerebellar artery and the rootlets of the trochlear nerve: illustrative case.

backgroundThe superior cerebellar artery (SCA) typically has the most consistent course of the infratentorial branches; however, variations do occur. Originating near the basilar artery (BA) bifurcation, the SCA proceeds to its pontomesencephalic segment, where it may contact the trochlear nerve (cranial nerve [CN] IV) or its rootlets emerging dorsally from the brainstem. OBSERVATIONS: During routine dissection, a previously undescribed SCA variation was identified. The left SCA arose as a single trunk from the BA and divided into the rostral trunk (RoTr) and caudal trunk. The RoTr then bifurcated into the medial hemispheric artery (inferior branch) and vermian artery (superior branch). The superior branch of the RoTr gave rise to the precerebellar artery, which coursed 3.2 mm before passing between two trochlear nerve rootlets in the rootlet exit zone. LESSONS: Understanding complex anatomical variations of the SCA and its relationship to CN IV is crucial for accurate diagnosis of the trochlear nerve dysfunction and for effective surgical planning. A thorough understanding of these variations enables physicians to anticipate potential challenges and adapt their approach accordingly. Intraoperative identification of unexpected vascular patterns underscores the importance of the surgeon's knowledge of anatomical variability, which may significantly impact both safety and surgical strategy. https://thejns.org/doi/10.3171/CASE25653.