Abstract
PURPOSE: The dural sigmoid sinus (SS) is a major surgical landmark. It is aimed to report an extraordinary and clinically significant anatomical variation- the mastoid pouch of the SS, which replaces the mastoid air cells. METHOD: The archived angioCT file of a 45 y.o. male was retrospectively studied on planar sections and by three-dimensional volume renderings. RESULTS: An expansive mastoid pouch of the left SS was found, measuring 1.74 cm in transverse diameter and 2.18 cm in sagittal diameter, replacing the typical mastoid air cell system. This SS pouch extended to the mastoid cortex and was covered by a robust (1.41 cm broad) tegmen sinus sigmoidei. The bony wall between the SS pouch and the mastoid portion of the facial canal was 4.65 mm thick. CONCLUSION: The marked venous encroachments into the mastoid region emphasise the necessity for comprehensive preoperative imaging and careful selection of surgical approaches to prevent inadvertent vascular compromise.