The Innovative Concept of Craniotomy in suboccipital retrosigmoid keyhole approach: anatomical study, technique nuances, and clinical application

Background : The suboccipital retrosigmoid approach is a classic approach for surgical access to cerebellopontine angle diseases. Previously, we identified a novel method for precise localization of keypoint, known as the "one point, two lines, two distances" theory. However, a comprehensive, safe method for craniotomy remains lacking. Objective : Based on the new landmark method of localization , this study aims to further describe the anatomical basis, surgical technique, and outcomes of the suboccipital retrosigmoid keyhole approach for craniotomy. Methods : Twelve adult specimens of skull were used for the study. The anatomical relationships between the keypoint were analyzed to establish a precise, rapid, and safe method for suboccipital retrosigmoid keyhole craniotomy. This method was then validated through cadaveric dissection. Furthermore, a retrospective analysis of surgical outcomes was performed on 122 clinical patients, assessing accuracy, safety, and exposure results. Results : Measurements from specimens of skull revealed that the up point of digastatic sulci roughly corresponds to the margin of the sigmoid sinus. In craniotomy simulations performed on 12 cadaveric specimens, we freed the bone flap in a "rear-down-front" direction after drilling at the key point. This process passed through the up point of digastatic sulci, with bone around the mastoid emissary vein being removed using a grinding drill, followed by resection of the residual bone along the margin of the sigmoid sinus. In all cadaver specimens, the formation of bone flap resulted in a well-exposed window. In the clinical cohort of 122 patients, keypoints were accurately located, and suitable bone windows were created with good exposure and without damage to important structures. Conclusion : The up point of digastatic sulci serves as a crucial reference point for keypoint localization. Craniotomy techniques based on this reference point provide a precise and safe approach for suboccipital retrosigmoid craniotomy.