Application of anatomy of anterior clinoid process and anterior clinoidectomy in neurosurgery / 中华神经医学杂志

The anterior clinoid process (ACP) is an important anatomical structure of the skull base. Some surgeries for intracranial lesions require to remove the ACP in order to achieve visual field exposure of the lesions and surrounding anatomical structure, and provide sufficient operating space. In this paper, the research progress in anatomy and variation of the ACP, methods of anterior clinoidectomy, and applications of anterior clinoidectomy in neurosurgical surgerys are summarized as follows.

Impact of Anterior Clinoid Process Pneumatization on Adjacent Anatomical Structures

The Anterior clinoid process is closely related to many important anatomical structures including vessels, nerves, and paranasal sinuses. In the majority of cases, this process is osseous, but its pneumatization has been recorded as an anatomic variant. Coronal CT scans of the head region that were done for thirty-seven patients at Tanta University hospitals were collected to be used in teaching radiological anatomy for medical students. During their routine investigation, a case of a female aged 21 years showed bilateral pneumatization of the anterior clinoid processes associated with some variants of the adjacent anatomical structures. These findings were discussed on anatomical basis with referral to their possible clinical implications. If a surgical removal of the anterior clinoid process is recommended, a comprehensive knowledge of its anatomy, pneumatization, and associated regional anatomic variants is crucial for neurosurgeons to avoid risky complications.

Measurement of Critical Structures around Paraclinoidal Area : A Cadaveric Morphometric Study

OBJECTIVE: Although removal of the anterior clinoid process (ACP) is essential surgical technique, studies about quantitative measurements of the space broadening by the anterior clinoidectomy are rare. The purposes of this study are to investigate the dimension of the ACP, to quantify the improved exposure of the parasellar space after extradural anterior clinoidectomy and to measure the correlation of each structure around the paraclinoidal area. METHODS: Eleven formalin-fixed Korean adult cadaveric heads were used and frontotemporal craniotomies were done bilaterally. The length of C6 segment of the internal carotid artery on its lateral and medial side and optic nerve length were checked before and after anterior clinoidectomy. The basal width and height of the ACP were measured. The relationships among the paraclinoidal structures were assessed. The origin and projection of the ophthalmic artery (OA) were investigated. RESULTS: The mean values of intradural basal width and height of the ACP were 10.82 mm and 7.61 mm respectively. The mean length of the C6 lateral and medial side increased 49%. The mean length of optic nerve increased 97%. At the parasellar area, the lengths from the optic strut to the falciform liament, distal dural ring, origin of OA were 6.69 mm, 9.36 mm and 5.99 mm, respectively. The distance between CN III and IV was 11.06 mm. CONCLUSION: With the removal of ACP, exposure of the C6 segments and optic nerve can expand 49% and 97%, respectively. This technique should be among a surgeon's essential skills for treating lesions around the parasellar area.

The Pterional Approach and Extradural Anterior Clinoidectomy to Clip Paraclinoid Aneurysms

OBJECTIVE: The surgical clipping of paraclinoid segment internal carotid artery aneurysms is considered difficult because of the complex anatomical location and important neighboring structures. Our experiences of pterional craniotomy and extradural anterior clinoidectomy (EAC) to clip paraclinoid aneurysms are reported herein. METHODS: We present two patients with paraclinoid aneurysms who underwent surgical clipping using pterional craniotomy and EAC. The clinical results and operative techniques were reviewed from the patients' medical records. RESULTS: EAC improves the surgical field in the suprasellar and periclinoid regions. Clinically, a good outcome was obtained in both cases. No surgical complications directly resulting from the EAC were observed. CONCLUSION: Favorable surgical results can be obtained with pterional craniotomy and EAC for the clipping of paraclinoid aneurysms. EAC is advocated for the clipping of paraclinoid aneurysms.

The Avoidance of Microsurgical Complications in the Extradural Anterior Clinoidectomy to Paraclinoid Aneurysms

OBJECTIVE: Paraclinoid segment internal carotid artery (ICA) aneurysms have historically been a technical challenge for neurovascular surgeons. The development of microsurgical approach, advances in surgical techniques, and endovascular procedures have improved the outcome for paraclinoid aneurysms. However, many authors have reported high complication rates from microsurgical treatments. Therefore, the present study reviews the microsurgical complications of the extradural anterior clinoidectomy for treating paraclinoid aneurysms and investigates the prevention and management of observed complications. METHODS: Between January 2004 and April 2008, 22 patients with 24 paraclinoid aneurysms underwent microsurgical direct clipping by a cerebrovascular team at a regional neurosurgical center. Microsurgery was performed via an ipsilateral pterional approach with extradural anterior clinoidectomy. We retrospectively reviewed patients' medical charts, office records, radiographic studies, and operative records. RESULTS: In our series, the clinical outcomes after an ipsilateral pterional approach with extradural anterior clinoidectomy for paraclinoid aneurysms were excellent or good (Glasgows Outcome Scale : GOS 5 or 4) in 87.5% of cases. The microsurgical complications related directly to the extradural anterior clinoidectomy included transient cranial nerve palsy (6), cerebrospinal fluid leak (1), worsened change in vision (1), unplanned ICA occlusion (1), and epidural hematoma (1). Only one of the complications resulted in permanent morbidity (4.2%), and none resulted in death. CONCLUSION: Although surgical complications are still reported to occur more frequently for the treatment of paraclinoid aneurysms, the permanent morbidity and mortality resulting from a extradural anterior clinoidectomy in our series were lower than previously reported. Precise anatomical knowledge combined with several microsurgical tactics can help to achieve good outcomes with minimal complications.

Pre -vs. Post-Anterior Clinoidectomy Measurements of the Optic Nerve, Internal Carotid Artery, and Optico-Carotid Triangle: A Cadaveric Morphometric Study

Anterior clinoid process is a small bony structure but it is very important regarding its location and relationships with neighboring neurovascular, dural, and bony structures. Removal of this process has been used in various modification of standard pterional approach. The authors have speculated how much expansion of operative window could be obtained with anterior clinoidectomy, so we measured the lengths of optic nerve, internal carotid artery, and the length and width of optico-carotid triangle(OCT) before and after extradural anterior clinoidectomy 17 times in 10 cadaveric heads. This procedure provided about two fold increase in the length of optic nerve and OCT, and over three fold expansion in the width of OCT. The results indicate that the addition of this relatively simple and easy procedure to standard approach makes the operative field more comfortable and safe than expected. We believe this procedure can be used routinely with or without combination of wide skull base exposure in cases of such lesions as belows: 1) lesions causing optic nerve or chiasmatic compression, 2) lesions encircling/covering the optic nerve and internal carotid artery, 3) lesions arising from or extending into the optic canal, orbital apex, and paraclinoid region, 4) suprasellar/parasellar lesions with limited operative windows(e.g. prefixed chiasm, infra-optic or subchiasmatic locations or adherence).