An anatomical study of the sigmoid sinus artery: Application to the transmastoid approach

Introduction: We aimed to investigate the morphological features of the artery that traverse the sigmoid sinus's lateral surface and to discuss this structure's clinical relevance. Methods: Ten sides from five cadaveric Caucasian heads were used for gross anatomical dissection to investigate the morphological features of the sigmoid sinus artery (SSA), and additional five sides were used for histological observation. Results: The SSA was found on eight out of ten sides (80%). The mean diameter of the SSA was 0.3 mm. The mean distance from the tip of the mastoid process to the artery was 20.3 mm. Histological observation identified extradural and intradural courses of SSA. The intradural course was further categorized into protruding and non-protruding types. In the protruding type, the SSA traveled within the dura but indented into the bone, making it more or less an intraosseous artery. In the non-protruding type, the SSA traveled within the dura but did not protrude into the bone but rather indented into the lumen of the SS. In all sections, both intradural and extradural courses were identified simultaneously. Conclusions: When the mastoid foramen is observed, it does not always only carry an emissary vein but also an artery. The SSA could be considered a "warning landmark" during bone drilling for the transmastoid approach.