1026. Analysis of the Neural Triangles of the Cerebellomedullary Cistern: An Improved Anatomical View

Authors: Leandro Borba Moreira; Ali Tayebi Meybodi, MD; Xiaochun Zhao; Mark Preul, MD; Michael Lawton (Phoenix, AZ)

Introduction: The vagoaccessory triangle (VAT) and triangles within are surgical corridors to neurovascular structures in the cerebellomedullary cistern (CMC). VAT is generally divided into two triangles: suprahypoglossal (SHT) and infrahypoglossal (IHT). We have anatomically reanalyzed VAT and triangles within to provide improved CMC anatomical understanding. We introduce the hypoglossal-hypoglossal triangle (HHT) formed by rootlets of hypoglossal nerve splayed over vertebral artery (VA) en route to hypoglossal canal. Methods: Twenty far-lateral cadaveric craniotomies were performed. CMC triangles areas were calculated. VA exposure and clipping lengths recorded for each triangle. Average distance from dural penetration point of VA to proximal and distal exposure points was calculated for each triangle. Ranges for different V 4 segments were examined for accuracy on a series of 30 PICA aneurysm angiograms with control intraoperative images. Results: Average areas of HHT and IHT did not show a statistically significant difference (74 ± 20.1mm 2 and IHT 64±12.4mm 2 , respectively), average area of SHT (131 ± 38.3mm 2 )was almost twice (p<.001). According to the adjacent triangle, V 4 -VA course could be divided into 3 segments: V 4i (IHT), V 4h (HHT), V 4s (SHT) average exposure lengths 8±2.7, 10±4.8, 10±3.2mm; clipping lengths 5 ± 3.1, 8 ± 4.6, 7 ± 3.0mm, respectively. Exposure lengths were not statistically different between triangles, neither were clipping lengths. Clipping and exposure lengths for individual V 4 segments were different in V 4i (p=.01) and V 4s (p=.04), but not V 4h . V 4i within 5–12mm, V 4h 14–24mm, V 4s > 26mm from dural penetration point. Using these ranges, predicting PICA triangle origin was performed with 76% accuracy in clinical series. In 6 cases, triangle of origin was partially predicted, only 1 case triangle of origin wrongly predicted. Conclusion: Our findings provide a deeper understanding of VAT and triangles within compared to previous concepts, showing that VAT should be divided into 3 triangles. V 4 subsegments may be approximated from imaging studies, which may help with pre-operative planning.