Endoscopic Endonasal Cavernous Sinus Surgery: An Anatomic Study

To the Editor: We read with great interest the article by Alfieri and Jho (1) about the endoscopic endonasal cavernous sinus anatomy and surgery. The authors dissected five adult cadaveric head specimens using 0-, 30-, and 70-degree 4-mm rod-lens endoscopes. The posterior wall of the cavernous sinus was approached via a paraseptal middle turbinectomy or by a middle meatal approach. The authors subdivided the internal carotid artery (ICA) at the posterior wall of the sphenoidal sinus into two main segments: the parasellar and the paraclival. They also subdivided the C4 segment (the cavernous segment) of Bouthillier et al.’s (2) classification into four segments: trigeminal, hidden, inferior horizontal, and anterior vertical segments. The vidian canal is a landmark that leads to the foramen lacerum, the mandibular nerve, and the pterygopalatine fossa. As the authors stated in the Discussion, many different classifications of the ICA have been reported, and the classification schema of Bouthillier et al. (2) may be the most agreeable. Their classification system considers the cavernous ICA as a C4 segment and adds a new segment: the lacerum or C3 segment. The petrolingual ligament is the border where the lacerum segment (C3) continues as the cavernous segment (C4). We studied the petrolingual ligament, the posteroinferior attachment of the lateral wall of the cavernous sinus, bilaterally in five cadaveric head specimens (3). The ligament is surgically important because of its identification as a landmark for dissection of the ICA during approaches to posterolateral intracavernous and extracavernous lesions. We were the first investigators to describe the triangle formed laterally by the petrolingual ligament; medially by the ICA; and posteriorly by the petrous apex, the dorsum sellae, and the petrosphenoidal ligament (Gruber’s ligament). This triangle is the area in which the VIth cranial nerve leaves Dorello’s canal and enters the cavernous sinus. We referred to the functional zone between the petrous and intracavernous segments of the ICA as the trigeminal segment because this area is covered by the trigeminal ganglion and the root (3). Bouthillier et al. (2) referred to this segment of the ICA as the lacerum segment, although the ICA does not pass through the foramen lacerum. Alfieri and Jho (1), however, subdivided the C4 segment of Bouthillier et al.’s classification schema into four segments: trigeminal, hidden, inferior horizontal, and anterior vertical segments. Well-known classical segments of the intracavernous ICA are the posterior vertical segment, the posterior bend, the horizontal segment, the anterior bend, and the anterior vertical segment. The new classification schema offered by Alfieri and Jho may be useful for endoscopic endonasal cavernous sinus anatomy and surgery. Use of the term trigeminal segment to refer to one subsegment of the intracavernous ICA might be confusing, however, considering that the trigeminal roots are not actually in the cavernous sinus but cover the lateral border of the cavernous sinus. The authors conducted an excellent endoscopic anatomic study. Ibrahim M. Ziyal Tunçalp Özgen