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Two-Piece OZ Craniotomy

Surgical Correlation

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Two-Piece OZ Craniotomy. A, The cranium has been positioned to show the position of the cuts along the roof and lateral wall of the orbit (red dashed line) following elevation of the first piece, the pterional flap. The sphenoid ridge along with the temporal squama has been drilled away. The cuts along the anterior root of zygoma (yellow line) and across the zygomatic body (black dashed line) are similar to those in the one-piece OZ craniotomy. A small notch has been drilled along the anterolateral wall of the temporal fossa (red crosshatched area). The supraorbital rim is divided lateral to the supraorbital notch and the cut along the orbital wall passes adjacent to the lateral edge of the superior orbital fissure. The cut along the lateral orbital wall passes through the already drilled small notch and into the lateral end of the inferior orbital fissure. The green arrow marks the lateral edge of the inferior orbital fissure. B, The inset shows the position of the scalp incision. The frontotemporal bone flap has been elevated and the remainder of the temporal squama has been removed. The dura has been elevated from the orbital roof and sphenoid ridge. A small notch has also been drilled along the anterolateral wall of the temporal fossa (red crosshatched area). The sphenoidal ridge has been drilled away until the temporal dura near the junction of the roof and the lateral wall of the orbit is reached. C, The attachments of the temporal dura have been freed and the dura has been elevated medially to expose the anterior clinoid process. D, The osteotomy (another specimen) divides the superior orbital rim, the orbital roof and lateral wall and extends from a point lateral to the supraorbital notch to the anterolateral edge of the inferior orbital fissure. The cut extends along the edge but not into the superior orbital fissure and ends in the lateral part of the inferior orbital fissure. E, The roof and lateral orbital wall have been elevated. The remaining bone medial to the superolateral edge of the superior orbital fissure and the anterior clinoid process, if needed, can be removed. F, The two-piece OZ craniotomy includes a bone flap similar to that of a frontotemporal (pterional) craniotomy and a second piece that includes part of the lateral and superior orbital rim and the roof and lateral wall of the orbit, a portion of the zygomatic body, and the anterior part of the zygomatic arch. G, Anterior view of the left orbit, comparing the extent of osteotomies in the one-piece (red dashed line) and two-piece (black dashed line) OZ craniotomies. In the two-piece OZ craniotomy the orbital roof and lateral wall are removed intradurally under direct vision, thus allowing for a more extensive orbitotomy. This two-piece approach permits the elevation of the orbital roof to extend nearer the superolateral edge of the superior orbital fissure than in the one-piece. H, Anterior view comparing the orbital osteotomies in a right one- and two-piece OZ craniotomy. Significantly more orbital roof and lateral wall is elevated in the two-piece as compared to one-piece OZ. The orbital roof makes up nearly 67% of the total orbitotomy of the two-piece, while comprising only 27% of the one-piece. (Images courtesy of AL Rhoton, Jr.)

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