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Wei-Hsin Wang, Stefan Lieber, Roger Neves Mathias, Xicai Sun, Paul A. Gardner, Carl H. Snyderman, Eric W. Wang, and Juan C. Fernandez-Miranda

OBJECTIVE

The foramen lacerum is a relevant skull base structure that has been neglected for many years. From the endoscopic endonasal perspective, the foramen lacerum is a key structure due to its location at the crossroad between the sagittal and coronal planes. The objective of this study was to provide a detailed investigation of the surgical anatomy of the foramen lacerum and its adjacent structures based on anatomical dissections and imaging studies, propose several relevant key surgical landmarks, and demonstrate the surgical technique for its full exposure with several illustrative cases.

METHODS

Ten colored silicone-injected anatomical specimens were dissected using a transpterygoid approach to the foramen lacerum region in a stepwise manner. Five similar specimens were used for a comparative transcranial approach. The osseous anatomy was examined in 32 high-resolution multislice CT studies and 1 disarticulated skull. Representative cases were selected to illustrate the application of the findings.

RESULTS

The pterygosphenoidal fissure is the synchondrosis between the lacerum process of the pterygoid bone and the floor of the sphenoid bone. It constantly converges with the posterior end of the vidian canal at a 45° angle, and its posterolateral end points directly to the lacerum foramen. The pterygoid tubercle separates the vidian canal from the pterygosphenoidal fissure, and forms the anterior wall of the lower part of the foramen lacerum. The lingual process, which forms the lateral wall of the foramen lacerum, was identified in 53 of 64 sides and featured an average height of 5 mm. The mandibular strut separates the foramen lacerum from the foramen ovale and had an average width of 5 mm.

CONCLUSIONS

This study provides relevant surgical landmarks and a systematic approach to the foramen lacerum by defining anterior, medial, lateral, and inferior walls that may facilitate its safe exposure for effective removal of lesions while minimizing the risk of injury to the internal carotid artery.

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Huy Q. Truong, Stefan Lieber, Edinson Najera, Joao T. Alves-Belo, Paul A. Gardner, and Juan C. Fernandez-Miranda

OBJECTIVE

The medial wall of the cavernous sinus (CS) is often invaded by pituitary adenomas. Surgical mobilization and/or removal of the medial wall remains a challenge.

METHODS

Endoscopic endonasal dissection was performed in 20 human cadaver heads. The configuration of the medial wall, its relationship to the internal carotid artery (ICA), and the ligamentous connections in between them were investigated in 40 CSs.

RESULTS

The medial wall of the CS was confirmed to be an intact single layer of dura that is distinct from the capsule of the pituitary gland and the periosteal layer that forms the anterior wall of the CS. In 32.5% of hemispheres, the medial wall was indented by and/or well adhered to the cavernous ICA. The authors identified multiple ligamentous fibers that anchored the medial wall to other walls of the CS and/or to specific ICA segments. These parasellar ligaments were classified into 4 groups: 1) caroticoclinoid ligament, spanning from the medial wall and the middle clinoid toward the clinoid ICA segment and anterior clinoid process; 2) superior parasellar ligament, connecting the medial wall to the horizontal cavernous ICA and/or lateral wall of the CS; 3) inferior parasellar ligament, bridging the medial wall to the anterior wall of the CS or anterior surface of the short vertical segment of the cavernous ICA; and 4) posterior parasellar ligament, which anchors the medial wall to the short vertical segment of the cavernous ICA and/or the posterior carotid sulcus. The caroticoclinoid ligament and inferior parasellar ligament were present in most CSs (97.7% and 95%, respectively), while the superior and posterior parasellar ligaments were identified in approximately half of the CSs (57.5% and 45%, respectively). The caroticoclinoid ligament was the strongest and largest ligament, and it was typically assembled as a group of ligaments with a fan-like arrangement. The inferior parasellar ligament was the first to be encountered after opening the anterior wall of the CS during an interdural transcavernous approach.

CONCLUSIONS

The authors introduce a classification of the parasellar ligaments and their role in anchoring the medial wall of the CS. These ligaments should be identified and transected to safely mobilize the medial wall away from the cavernous ICA during a transcavernous approach and for safe and complete resection of adenomas that selectively invade the medial wall.

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Juan C. Fernandez-Miranda, Nathan T. Zwagerman, Kumar Abhinav, Stefan Lieber, Eric W. Wang, Carl H. Snyderman, and Paul A. Gardner

OBJECTIVE

Tumors with cavernous sinus (CS) invasion represent a neurosurgical challenge. Increasing application of the endoscopic endonasal approach (EEA) requires a thorough understanding of the CS anatomy from an endonasal perspective. In this study, the authors aimed to develop a surgical anatomy–based classification of the CS and establish its utility for preoperative surgical planning and intraoperative guidance in adenoma surgery.

METHODS

Twenty-five colored silicon–injected human head specimens were used for endonasal and transcranial dissections of the CS. Pre- and postoperative MRI studies of 98 patients with pituitary adenoma with intraoperatively confirmed CS invasion were analyzed.

RESULTS

Four CS compartments are described based on their spatial relationship with the cavernous ICA: superior, posterior, inferior, and lateral. Each compartment has distinct boundaries and dural and neurovascular relationships: the superior compartment relates to the interclinoidal ligament and oculomotor nerve, the posterior compartment bears the gulfar segment of the abducens nerve and inferior hypophyseal artery, the inferior compartment contains the sympathetic nerve and distal cavernous abducens nerve, and the lateral compartment includes all cavernous cranial nerves and the inferolateral arterial trunk. Twenty-nine patients had a single compartment invaded, and 69 had multiple compartments involved. The most commonly invaded compartment was the superior (79 patients), followed by the posterior (n = 64), inferior (n = 45), and lateral (n = 23) compartments. Residual tumor rates by compartment were 79% in lateral, 17% in posterior, 14% in superior, and 11% in inferior.

CONCLUSIONS

The anatomy-based classification presented here complements current imaging-based classifications and may help to identify involved compartments both preoperatively and intraoperatively.