Quantitative analysis of the working area and angle of attack for the retrosigmoid, combined petrosal, and transcochlear approaches to the petroclival region

Object. The authors quatitatively assessed the working areas and angles of attack associated with retrosigmoid 2m (RS), combined petrosal (CP), and transcochlear (TC) craniotomies. Methods. Four silicone-injected cadaveric heads were bilaterally dissected using three approaches progressing from the least to the most extensive. Working areas were determined using the Optotrak 3020 system oil the tipper and middle thirds of the petroclivus and brainstem. Angles of attack were studied using the Elekta SurgiScope at the Dorello canal and the origin of the anterior inferior cerebellar artery (AICA). The TC approach provided significantly greater (p < 0.001) working areas at the petroclivus (755.6 +/- 130.1 mm(2)) and brainstem (399.3 +/- 68.2 mm(2)) than the CP (354.1 +/- 60.3 and 289.7 +/- 69.9 mm(2)) and RS approaches (292.4 +/- 59.9, 177.2 +/- 54.2 mm(2), respectively). The brainstem working area associated with the CP approach vas significantly larger (p < 0.001) than that associated with the RS route. There was no difference in the petroclival working area comparing the CP and RS approaches (p = 0.149). The horizontal and vertical angles of attack achieved using the TC approach were wider than those of the CP and RS at the Dorello canal and the origin of the AICA (p < 0.001). Conclusions. The CP approach offers a more extensive working area than the RS for lesions involving the anterolateral surface of the brainstem, but not for petroclival lesions. The TC approach provides the widest corridor, improving the working, area and angle of attack to both areas, but hearing must be sacrificed and the facial nerve is at risk.