A, The trigeminal posterior root, ganglion, and three divisions have been exposed by removing the dura from the lateral wall of Meckel’s cave and the cavernous sinus. The posterior root enters the midpons below the SCA and is intertwined with the branches of the superior petrosal vein. B, The SCA loops downward and, at the junction of the rostral and caudal trunks, contacts the posterior trigeminal root at the pontine junction. The cerebellar lip projects forward and may block access to the junction of the trigeminal nerve and pons in the retrosigmoid approach. C, SCA with an early bifurcation. The rostral trunk loops downward and indents the upper surface of the trigeminal nerve. D, Another SCA passes around the pons and bifurcates into its rostral and caudal trunks above the trigeminal root entry zone. (Images courtesy of AL Rhoton, Jr.)