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 the mastoid canal is reported here. In 7 of 161 patients who underwent retromastoid craniectomy, the postoperative soft tissue window image computed tomographic scans demonstrated a hypodense mass in the ipsilateral 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 masses in the sigmoid sinus was confirmed 1 month to 2 years after surgery. These computed tomographic findings suggested that this abnormal hypodense mass might be a migrated fragment of the bone wax that had been used for the control of venous bleeding from the mastoid emissary vein, because each of the seven affected patients had a large mastoid foramen and a large quantity of bone wax had been needed to control the bleeding during retromastoid craniectomy. No other material with the potential to migrate into the sigmoid sinus had been applied as a packing material. In two of the seven patients, venous magnetic resonance angiography after surgery demonstrated that the ipsilateral sigmoid sinus was not patent and the computed tomographic scans also revealed that the hypodense masses occupied the sigmoid sinus. It is concluded that the intrasurgical application of a large quantity of bone wax to control the bleeding from the large emissary veins carries a risk of the migration of bone wax into the sigmoid sinus.(ABSTRACT TRUNCATED AT 250 WORDS)