Paratrigeminal, Paraclival, Precavernous, or All of the Above? A Circumferential Anatomical Study of the C3-C4 Transitional Segment of the Internal Carotid Artery.

BACKGROUND: Although the term paraclival carotid pervades recent skull base literature, no clear consensus exists regarding boundaries or anatomical segments. OBJECTIVE: To reconcile various internal carotid artery (ICA) nomenclatures for transcranial and endoscopic-endonasal perspectives, we reexamined the transition between lacerum (C3) and cavernous (C4) segments using a C1-C7 segments schema. In this cadaveric study, we obtained a 360°-circumferential view integrating histological, microsurgical, endoscopic, and neuroradiological analyses of this C3-C4 region and identified a distinct transitional segment. METHODS: In 13 adult, silicone-injected, formalin-fixed cadaveric heads (26 sides), transcranial-extradural-subtemporal and endoscopic-endonasal CT-guided dissections were performed. A quadrilateral area was noted medial to Meckel's cave between cranial nerve VI, anterolateral and posterolateral borders of the lateral-paratrigeminal aspect of the precavernous ICA, and posterior longitudinal ligament. Endoscopically, a medial-paraclival aspect was defined. Anatomical correlations were made with histological and neuroradiological slides. RESULTS: We identified a distinct precavernous C3-C4 transitional segment. In 18 (69%) specimens, venous channels were absent at the quadrilateral area, on the paratrigeminal border of the precavernous ICA. A trigeminal membrane, seen consistently on the superior border of V2, defined the lateral aspect of the cavernous sinus floor. The medial aspect of the precavernous ICA corresponded with the paraclival ICA. CONCLUSION: Our study revealing the juncture of 2 complementary borders of the ICA, endoscopic endonasal (paraclival) and transcranial (paratrigeminal), reconciles various nomenclature. A precavernous segment may clarify controversies about the paraclival ICA and support the concept of a "safe door" for lesions involving Meckel's cave, cavernous sinus, and petrous apex.

Extension of the one-piece orbitozygomatic frontotemporal approach to the glenoid fossa: cadaveric study.

OBJECTIVE: Resection of the glenoid fossa has been described as part of cranial approaches to the clivus and subtemporal approaches. However, radical resection carries a significant risk of postoperative temporomandibular joint dysfunction. We examine a simple variation of our previously described one-piece frontotemporal orbitozygomatic (FTOZ) osteotomy that adds en bloc resection of the root of the zygomatic arch and a portion of the glenoid fossa. METHODS: Five cadaveric fixed heads injected with colored silicone underwent an FTOZ osteotomy that extended to the root of the zygomatic arch and glenoid fossa. RESULTS: A step-by-step guide to the surgical technique is described, with illustrations to depict the glenoid fossa keyhole and bony cuts that free the zygomatic arch and portions of glenoid fossa. The first cut was made through the posterior root, and the second cut was made through the anterior root of the zygomatic arch. CONCLUSION: In this cadaveric study, extension of the one-piece FTOZ approach included the posterior root of the zygoma and the lateral part of the glenoid fossa. En bloc resection of the glenoid fossa and root of the zygomatic arch, together with the FTOZ osteotomy, facilitated reconstruction of the temporomandibular joint and increased the amount of exposure obtained with this FTOZ osteotomy. Comprehensive understanding of functional outcomes awaits further clinical study.