One-Piece OZ Craniotomy. A, The cranium has been rotated to the left to show the right frontotemporal area and the position of the keyhole and the cuts extending from the burr holes. The first cut (Cut 1) extends from the keyhole inferiorly along the lateral orbital wall to the inferior orbital fissure. The cut across the zygomatic body (Cut 2) is made approximately 1 cm below the junction of the angle formed by the frontal and zygomatic processes of the temporal bone and also extends, at its deep end, into the anterolateral part of the inferior orbital fissure as does Cut 1. The third cut (Cut 3) crosses near the anterior root of zygomatic process of the temporal bone. The intraorbital cut (Cut 4) along the roof of the orbit and across the superior orbital rim is not shown in this view, but is shown in G and H. The fifth cut (Cut 5) connects the anterior frontal and posterior temporal burr holes, and the final cut (Cut 6) extends from the temporal burr hole anteriorly to the keyhole and crosses the branches of the middle meningeal artery. B, Lateral view of the left fronto-orbital region. At its anterior end, the frontosphenoid suture, which separates the greater wing of the sphenoid bone from the frontal bone, joins the sphenozygomatic and frontozygomatic sutures at a point referred to as the three suture junction. At its posterior end, the frontosphenoid suture meets the coronal and parietosphenoid sutures. The pterion is located over the upper part of the greater sphenoid wing and approximates the site of the lateral end of the sphenoid ridge. In a previous study, it was found that the best site for the keyhole was on the frontosphenoid suture approximately 5 mm behind the three suture junction. C, Anterior view of the right orbit in another specimen. The frontozygomatic suture separates the zygomatic process of the frontal bone above from the frontal process of zygoma below, and runs backward to meet the sphenozygomatic and frontosphenoid sutures at a junctional point, referred to as the three suture junction The best position for the keyhole, based on our previous study, is over the frontosphenoid suture centered approximately 5 mm behind the three suture junction. D, The bone along the frontosphenoid suture has been removed to expose the lateral border of the roof and posterior wall of the orbit. The point at which the frontosphenoid suture crossed the roof of the orbit, an appropriate site for the keyhole to expose both the supraorbital dura and periorbita, is referred to as the cross point. The distance between the cross point and the three suture junction (a) averaged 6.3 mm (range, 3.4–8.3 mm). The average angle formed by a line extending vertically along the lateral orbital rim and a line extending along the lateral edge of the orbital roof (b) was 61 degrees (c). E, Lateral view of the cranium showing the bone cuts extending from the orbital and frontal compartments of the keyhole. The keyhole should expose the frontal dura in its upper half and the periorbita in the lower half with the roof of the orbit in between. The first cut extends from the orbital compartment of the keyhole inferiorly to the anterolateral part of the inferior orbital fissure. The last cut (Cut 6) extends from the temporal burr hole into the frontal compartment of the keyhole and crosses the branches of the middle meningeal artery. The other cuts are as outlined in A. F, Enlarged view of the keyhole, which exposes the periorbita its lower part, the frontal dura in the upper part, and the orbital roof between the two. The inset shows the osseous relationships. (Images courtesy of AL Rhoton, Jr.)