The authors report two surgical cases with acoustic neurinoma in which haemorrhagic infarction occurred via a compromise in cerebral deep venous outflow. In both cases, surgery was performed via the posterior petrosal approach, and the neurinomas were completely removed. In the first case, the haemorrhagic infarction was considered to have resulted from transection of the tentorial sinus, the presence of which had not been predictable by preoperative angiography. In the second case, the haemorrhagic infarction was caused by a coagulation of the petrosal vein, which was firmly adherent to a tumour. With the posterior petrosal approach, meticulous care is necessary to preserve the deep anastomotic veins into and around the cerebellar tentorium. Thereby, catastrophic morbidity related to compromised deep cerebral venous outflow can be avoided.