Feasibility for Side-to-Side PICA-PICA Bypass and Variations: A Correlative Cadaver and Computed Tomography Angiogram Study

BACKGROUND AND OBJECTIVES: The posterior inferior cerebellar artery (PICA) is highly variable artery with a complex anatomy that limits surgical strategies, including PICA-PICA bypass. Detailed anatomic criteria for bypass feasibility remain incompletely defined. This study aimed to define the anatomic criteria for side-to-side PICA-PICA bypass and evaluate how PICA variations, especially at the origin, affect bypass feasibility and preoperative planning. METHODS: Dissections were performed on 25 cadavers to evaluate PICA origins and anatomic variations affecting bypass feasibility. We measured the PICA diameter, origin location, proximity to surrounding structures, and the presence/absence of bilateral caudal loops (BCL). Subsequently, we retrospectively analyzed 120 computed tomography angiograms to assess prevalence of anatomic configurations favorable for PICA-PICA bypass in a broader population. RESULTS: PICA-PICA bypass was feasible in 13 of 25 cadavers (52%), including 7 (54%) ideal and 6 (46%) barely feasible cases. Bypass was infeasible in 12 specimens (48%) because of absent or hypoplastic PICA, excessive intervessel distance, or unfavorable BCL configuration. BCLs were identified in 18 specimens (72%); however, bypass was feasible in 9 cases (50%). Feasible cases demonstrated shorter origin-to-dura distances (15.6-16.2 mm) than infeasible cases (20.1 mm). PICA origins were classified along the V4 vertebral artery as premedullary, lateral medullary, or postmedullary, with lateral medullary origin most common (61.1%) and strongly associated with BCL presence (95.5%). Computed tomography angiogram analysis demonstrated a mean PICA caliber of 1.54 mm with a mean bilateral difference of 0.28 mm. Overall BCL prevalence was 67%, decreasing as origin-to-dura distance increased. CONCLUSION: PICA-PICA bypass feasibility is strongly determined by PICA origin, caudal loop formation, and bilateral vessel proximity. Distant origins and absent or hypoplastic PICAs significantly reduce bypass feasibility. These findings support the use of preoperative imaging to identify anatomic configurations that favor PICA-PICA bypass and guide surgical planning.