Occipital transtentorial approach selected based on venous anatomy for a vermian cavernous malformation: illustrative case.

backgroundCavernous malformations of the superior cerebellar vermis beneath the tentorium are rare and surgically challenging because approach selection must account for lesion location and venous anatomy. OBSERVATIONS: A 69-year-old man presented with vertigo, nausea, and truncal ataxia caused by hemorrhage from a cavernous malformation of the superior cerebellar vermis. Repeated CT during the first 5 days after admission showed hematoma enlargement with worsening symptoms. Preoperative CT venography revealed bilateral hypoplastic transverse sinuses with dominant occipital and marginal sinuses, indicating atypical posterior fossa venous drainage. No major occipital bridging vein was identified along the planned operative corridor. Because of hematoma enlargement, symptom progression, and the risk of sudden deterioration associated with a posterior fossa lesion, early surgery was performed. An occipital interhemispheric transtentorial approach was selected to avoid dominant midline venous drainage pathways and provide a direct trajectory to the lesion. Indocyanine green videoangiography confirmed the absence of a major tentorial sinus along the planned incision line. Complete resection was achieved without venous injury, ischemic complications, or postoperative visual field deficit on clinical assessment. LESSONS: In superior vermian lesions, patient-specific venous drainage patterns may be decisive in approach selection. https://thejns.org/doi/10.3171/CASE25996.