Microsurgical anatomy of the tentorial sinuses

Variations of the tentorial sinus of cadaver cerebellar tentoria were examined under a surgical microscope. The tentorial sinuses were classified into four groups: Group I, in which the sinus receives venous blood from the cerebellar hemisphere; Group II, in which the sinus drains the cerebellum; Group III, in which the sinus originates in the tentorium itself; and Group IV, in which the sinus originates from a vein bridging to the tentorial free edge. The tentorial sinuses of Groups I and II were frequently located in the posterior portion of the tentorium. The sinuses of Group I were short and most freqeuntly present in the lateral portion of the tentorium. The tentorial sinuses of Group II, which was usually large and drained into the dural sinuses near the torcular, were separated into five subtypes according to the draining veins and direction of termination. The tentorial sinuses of Groups III and IV were located near the tentorial free edge or the straight sinus. The draining patterns of the tentorial sinuses and their draining veins (so-called 'bridging veins') were present in most cases. Knowledge of this anatomy can benefit the neurosurgeon carrying out repair near or on the cerebellar tentorium.