Anatomic position of the asterion

OBJECTIVE: The asterion is defined as the junction of the lambdoid, parie toomastoid, and occipitomastoid sutures. The asterion has been used as a landmark in lateral approaches to the posterior fossa. However, its reliability as a landmark comes into question considering the apparent variability of its position. This study was performed to determine the reliability of the asterion as a surgical landmark. METHODS: One hundred dried skulls were obtained for study. A 2-mm drill hole was placed at file asterion an each side. The position of the drill hole on the inner surface of the skull was next determined and recorded. RESULTS: The asterion was located over the posterior fossa dura in 32% on the right and 25% on the left its position was over the transverse or sigmoid sinus complex in 61% on the right and 66% on the left. The landmark was located above the transverse-sigmoid sinus complex in 7% on the right and 9% on the left. CONCLUSIONS: The asterion is not a strictly reliable landmark in terms of locating the underlying posterior fossa dura, its location is very often directly over the transverse-sigmoid sinus complex. Burr holes placed at the asterion may often open the bone directly over the sinus, leading to potential damage.