Introduction: The superior petrosal vein, one of the most constant and largest venous structures in the posterior fossa, may result in venous complications if occluded. The purpose of this study is to call attention to a unique variant in which the superior petrosal veins and sinus were absent, and venous drainage was through the galenic and tentorial groups.

Methods: Anatomical dissection of one formalin-fixed adult head, in which the left superior petrosal vein and sinus were not present. Also, a detailed analysis of venographic images of a patient without any identifiable superior petrosal vein nor sinus.

Results: The superior petrosal veins are 1-3 bridging veins draining into the superior petrosal sinus, as the major drainage of the petrosal group. In the cases described, the superior petrosal vein and sinus were absent and venous drainage was through the galenic and tentorial groups, including the lateral mesencephalic or bridging vein on the cerebellar tentorial surface.

Conclusions: In these unique cases, in which the superior petrosal sinus and veins are absent, care should be directed to preserving the collateral drainage through the galenic and tentorial tributaries. Although surgical strategies for intraoperative management and preservation of venous structures are still controversial, knowledge of the possible anatomical variations are considered to be essential to improve surgical outcomes.

Patient Care: Recognizing the multiple variation of the posterior fossa veins will help to avoid potential complication of the posterior fossa surgeries.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the various anatomy of posterior fossa veins, and 2) Discuss the venous complications of posterior fossa surgeries.

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