Fig. 2

a Operative CT venogram demonstrating subtotal occlusion of the right sigmoid sinus, with severe luminal narrowing on the posterior side. The emissary vein was found downstream of the severe stenosis. The tumor (asterisk) is located inside the sigmoid sinus. b Right presigmoid craniectomy was performed. After drilling the petrosal bones, very high pressure was found in the transverse and sigmoid sinuses. c Intraoperative indocyanine green fluorescence angiogram revealing a mass lesion as a blood flow defect. The mass was located inside the sigmoid sinus. d–f The tumor was observed after retraction of the dura and sinus, without dura or sinus wall incision. The tumor was extruded out spontaneously, because of the high pressure in the sinus. The extra sinus part of the tumor was removed first, and then the tumor was followed into the sinus. The tumor was located predominantly involving the sigmoid sinus