MASTOID CANAL AND MIGRATED BONE WAX IN THE SIGMOID SINUS - TECHNICAL REPORT

A STUDY OF the migration of bone wax into the sigmoid sinus through th e mastoid canal is reported here. In 7 of 161 patients who underwent r etromastoid craniectomy, the postoperative soft tissue window image co mputed tomographic scans demonstrated a hypodense mass in the ipsilate ral sigmoid sinus. The density value of the hypodense mass ranged from -34 to -79 Hounsfield units, which was neither as low as that of air nor as high as that of cerebrospinal fluid, but was comparable to that of fat tissue or bone wax. The continued presence of all of these mas ses in the sigmoid sinus was confirmed 1 month to 2 years after surger y. These computed tomographic findings suggested that this abnormal hy podense mass might be a migrated fragment of the bone wax that had bee n used for the control of venous bleeding from the mastoid emissary ve in, because each of the seven affected patients had a large mastoid fo ramen and a large quantity of bone wax had been needed to control the bleeding during retromastoid craniectomy. No other material with the p otential to migrate into the sigmoid sinus had been applied as a packi ng material. In two of the seven patients, venous magnetic resonance a ngiography after surgery demonstrated that the ipsilateral sigmoid sin us was not patent and the computed tomographic scans also revealed tha t the hypodense masses occupied the sigmoid sinus. It is concluded tha t the intrasurgical application of a large quantity of bone wax to con trol the bleeding from the large emissary veins carries a risk of the migration of bone wax into the sigmoid sinus. Care should be taken in the management of the emissary veins, and the use of bone wax should b e minimized in order to prevent sigmoid sinus occlusion.