Refined and simplified surgical landmarks for the MacCarty keyhole and orbitozygomatic craniotomy

Precise placement of the MacCarty keyhole, a burr hole simultaneously exposing the anterior cranial fossa floor and orbit, provides accurate, efficient entry for orbitozygomatic and supraorbital craniotomies. To locate the optimal keyhole site, previous studies have used superficial landmarks that, in our experience, are not always visible or consistent on older crania.

Therefore, we present a technique for accurate keyhole placement using landmarks that are easily visible across age ranges.

From inside the cranium, 1-mm burr holes were placed along the anterior junction of the floor and lateral wall of the anterior cranial fossa in 50 adult skulls (100 sides, with calvaria removed). Additionally, from inside the orbit, 1-mm burr holes were placed into the lateral orbital roof. Exit sites of intracranial and intraorbital burr holes were referenced to the frontozygomatic suture. The center of the site between the exiting intracranial and intraorbital holes was deemed the best location for the keyhole.

The keyhole center was 6.8 mm (mean) superior and 4.5 mm (mean) posterior to the frontozygomatic suture, which was easily identified on all specimens. Although this keyhole center was slightly more superior on right sides than left, this was not statistically significant. In a minority of specimens, the keyhole was located near the meningo-orbital foramen (22%) and the lateral extent of the frontal sinus (2%).

We defined an alternative method for locating the MacCarty keyhole, based on a reliable external landmark, approximately 7 mm superior and 5 mm posterior to the frontozygomatic suture.