The anterior condylar confluence of Trolard and its venous tributaries: an anatomical review

Abstract The anterior condylar confluence (ACC) of Trolard is a small extracranial venous plexus at the external orifice of the hypoglossal canal. Described over 150 years ago and present in the classical French anatomical literature, it was largely absent from the Anglophone radiological and surgical literature until the corrosion-cast study of San Millán Ruíz et al. (2002). It is the venous crossroads of the craniocervical junction, linking the posterior fossa dural sinuses, the internal jugular vein and the vertebral venous system. This structured anatomical review, illustrated with retrospectively selected MR and CT angiographic examinations, synthesises the anatomy of the confluence and of the ten venous channels reported to communicate directly or indirectly with ACC territory: the anterior, lateral and posterior condylar veins, branches of the internal jugular vein and its bulb, the inferior petrosal sinus, the inferior petro-occipital vein, the internal carotid artery venous plexus of Rektorzik, the prevertebral venous plexus, the marginal sinus and the clival diploic veins. For each, we collate the reported prevalence, osseous conduit, connected territories, and clinical relevance, and we state the denominators explicitly, since they differ by cast, side, junction, and subject. Two themes recur. The confluence is valveless throughout and reverses its drainage direction with posture, so the channels that join it form a bidirectional network rather than tributaries of a sinus. Targeted anatomical and imaging studies consistently identified the ACC, whereas the visibility and reported prevalence of several individual connections varied substantially across methods. Knowledge of this anatomy is required for far-lateral, transcondylar and endoscopic approaches, for transvenous access to the cavernous sinus, and for recognising fistulae of the region.