The asterion, derived from the Greek word asterion meaning “starry,” is an anatomical landmark on the human skull.
The asterion is made up of the junction of the occipital bone, the temporal bone, and the parietal bone. Its definition can also be a confluence of the lambdoid suture which is the junction of the occipital and parietal bones, the occipitomastoid suture, which is a junction of the occipital and temporal bones, and the parietomastoid suture, which is a junction of the parietal and temporal bones. It is a visible landmark on the human skull seen when removal of the soft tissue from the bony surfaces has taken place.
The asterion is a clinically significant piece of human cranial anatomy primarily for its utilization as a landmark in the retrosigmoid approach to skull base surgery. This technique is important for tumor resection from the cerebellopontine angle, such as with vestibular schwannoma removal. A 2007 study of dried human skulls published in the Chinese Medical Journal by Xia et al., sought to provide the best location on the surface anatomy of the skull through which to drill to perform an endoscopic retrosigmoid keyhole approach in skull base minimally invasive surgery. The authors found that a hole 2.0 cm in diameter placed at the midpoint between the tip of the mastoid and the asterion was the best location from which to access the structures of the cerebellopontine angle.
The asterion also potentially plays a part in the placement of hearing implants. In a 2018 study published in Otology & Neurotology, Arnold et al. state the need for an alternative site for implantation of the floating mass transducer of a bone conduction hearing implant, which ordinarily is implanted on the mastoid. The authors state that for patients with prior mastoid surgery or anatomical difficulties precluding appropriate placement of the mass transducer, an alternative method should be in place. They propose a retrosigmoid approach, using pre-operative computed tomography scanning and avoiding the sigmoid sinus by targeting a point approximately 1.9 cm posterior and 1.7 cm inferior to the asterion, and 3.3 cm posterior and 2.1 cm superior to the mastoid notch.