A Six-Surface System to Describe Anatomy of Anterior Clinoid Process and Its Application in Anterior Clinoidectomy and Resection of Paraclinoid Meningioma.

OBJECTIVE: The anterior clinoid process (ACP) is surrounded by nerves and vessels that, together, constitute an intricate anatomical structure with variations that challenges the performance of individualized anterior clinoidectomy in treating lesions with different extents of invasion. In the present study, we established a 6-surface system for the ACP based on anatomical landmarks and analyzed its value in guiding ACP drilling and resection of paraclinoid meningiomas. METHODS: Using the anatomical characteristics of 10 dry skull specimens, we set 9 anatomical landmarks to delineate the ACP into 6 surfaces. Guided by our 6-surface system and eggshell technique, 5 colored silicone-injected anatomical specimens were dissected via a frontotemporal craniotomy to perform anterior clinoidectomy. Next, 3 typical cases of paraclinoid meningioma were selected to determine the value of using our 6-surface system in tumor resection. RESULTS: Nine points (A-H and T) were proposed to delineate the ACP surface into frontal, temporal, optic nerve, internal carotid artery, cranial nerve III, and optic strut surfaces according to the adjacent tissues. Either intradurally or extradurally, the frontal and temporal surfaces could be identified and drilled into depth, followed by skeletonization of the optic nerve, cranial nerve III, internal carotid artery, and optic strut surfaces. After the residual bone was removed, the ACP was drilled off. In surgery of paraclinoid meningiomas, our 6-surface system provided great benefit in locating the dura, nerves, and vessels, thus, increasing the safety of opening the optic canal and relaxing the oculomotor or optic nerves and allowing for individualized ACP drilling for meningioma removal. CONCLUSIONS: Our 6-surface system adds much anatomical information to the classic Dolenc triangle and can help neurosurgeons, especially junior ones, to increase their understanding of the paraclinoid spatial structure and accomplish individualized surgical procedures with high safety and minimal invasiveness.

A New Practical Method Based on MRI to Individually Localize the Transverse-Sigmoid Sinus Junction in Retrosigmoid Craniotomy: A Retrospective Before-After Study.

Background: Although the asterion has long been used as a skeletal surface marker of the transverse-sigmoid sinuses junction (TSSJ) point in the retrosigmoid approach, abundant evidence shows that the relationship between asterion and TSSJ point varies greatly. In recent years, new technologies have been developed, such as neuronavigation and three-dimensional volume rendering imaging, that can guide in exposing the TSSJ point individually. However, they are not only expensive but also difficult to apply in emergency surgery. Objective: To introduce a quick, practical, and low-cost new method for locating the TSSJ point precisely. Methods: In this retrospective before-after study, the test group located the TSSJ point with our new method during a 6-month period, while the control group used asterion as a surface landmark to estimate the TSSJ during the preceding 6 months. The primary outcome is the immediate exposure rate of the TSSJ point by the initial burr hole. Results: There were 60 patients in both control and test groups as no significant difference in the general clinical characteristics of both groups were observed. The new three-step method significantly increased the TSSJ exposure rate by initial burr hole compared with the control group (96.67% vs. 53.33%, P = 0.0002). Moreover, the total bone loss and craniotomy duration were significantly reduced by the new method. Incidence of sinus injury (10% vs. 6.6%), post-operation infection (3.33% vs. 3.33%), and CSF leakage (3.33% vs. 0%) were similar. Conclusions: The novel three-step approach accurately locates TSSJ points in retrosigmoid craniotomy, reduces bone defects, saves time, and does not increase the risk of sinus injury, infection, and CSF leakage.