Transhorizontal fissure approaches to the middle cerebellar peduncle: quantitative anatomical analyses of the retrosigmoid, extended retrosigmoid, and presigmoid-retrolabyrinthine approaches

Pontine cavernous malformation (CM) resection requires thorough surgical planning to minimize morbidity and recurrence. This study compared posterolateral middle cerebellar peduncle (MCP) access after opening the interlobular triangle via the retrosigmoid (RS), extended retrosigmoid (xRS), and presigmoid-retrolabyrinthine (PSRL) approaches. The 3 approaches were performed in 6 cadaveric heads (12 sides). The interlobular triangle was configured over the MCP after dissecting the transhorizontal fissure. Quantitative comparisons of the MCP exposure area, volume of surgical freedom (VSF), and anteroposterior and rostrocaudal angles of attack (AOA) at the posterolateral MCP were completed. No significant difference was found for MCP exposure. The PSRL approach produced a VSF similar to the xRS approach (120 [44.8] mm3 vs 114.7 [47.3] mm3, p=0.80), and the PSRL and xRS had significantly greater VSF than the RS approach (63 [23.4] mm3; p<0.001 for both). The xRS (41.6° [7.4°]) and PSRL (47° [7.8°]) approaches had significantly larger anteroposterior AOAs than the RS (38.5° [7.4°]) approach (p<0.001, p=0.007). The PSRL approach had a mean (SD) 15.3° (5.4°) and 29° (5.2°) anterior angle advantage in the anteroposterior AOA over the xRS and RS approaches, respectively. The PSRL- and xRS-transhorizontal fissure approaches were superior to the RS-transhorizontal fissure approach for all instrument maneuverability parameters in the posterolateral MCP. The former 2 approaches were preferable for access to lateral pontine CMs, especially those with dorsal extensions. The xRS approach compensates for disadvantages of the RS and PSRL approaches to achieve surgical corridors for extensive central pontine CM resection.