Tag: transtentorial

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Application of Topographical Anatomy of the Trochlear Nerve in Transtentorial Approaches: An Anatomic Study

Operative Neurosurgery 28:705–711, 2025

his study examines the topographical anatomy of the trochlear nerve in relation to the free edge of the tentorium (FET) for safer transtentorial surgical approaches. It identifies safe zones for FET transection, minimizing injury risk to the trochlear nerve, crucial for surgeries involving the cavernous sinus.

• Study Focus: The study investigates the relationship between the trochlear nerve (CN IV), oculomotor nerve (CN III), and the free edge of tentorium (FET) to identify a safe zone for surgical maneuvers.

• Methods: Ten embalmed specimens were analyzed using digital microcalipers to measure morphometric details such as the distance between CN IV and CN III.

• Key Findings: CN IV pierces the deep layer of the FET and continues within it before entering the cavernous sinus. A nerve-free portion of FET averages 1.93 mm, with significant variability among specimens.

• Surgical Implications: Transection of the FET poses the lowest risk of CN IV injury if performed less than 2 mm or more than 10 mm posterior to the oculomotor porus (OP).

• Anatomical Observations: The FET is composed of deep and superficial layers, with the deep layer continuous with the petrous bone dura.

• Clinical Relevance: Knowledge of the topographical anatomy of CN III and CN IV is crucial for safe surgical approaches, especially in cases involving tumors or aneurysms.

• Limitations: The study’s experimental nature and limited sample size may not fully capture the anatomical variance encountered in vivo.

• Conclusion: The study provides essential anatomical guidance for reducing the risk of nerve injury during transtentorial surgical approaches.

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Transtentorial transcollateral sulcus approach to the ventricular atrium

J Neurosurg 126:1246–1252, 2017

Conventional approaches to the atrium of the lateral ventricle may be associated with complications related to direct cortical injury or brain retraction. The authors describe a novel approach to the atrium through a retrosigmoid transtentorial transcollateral sulcus corridor.

METHODS: Bilateral retrosigmoid craniotomies were performed on 4 formalin-fixed, colored latex–injected human cadaver heads (a total of 8 approaches). Microsurgical dissections were performed under 3× to 24× magnification, and endoscopic visualization was provided by 0° and 30° rigid endoscope lens systems. Image guidance was provided by coupling an electromagnetic tracking system with an open source software platform. Objective measurements on cortical thickness traversed and total depth of exposure were recorded. Additionally, the basal occipitotemporal surfaces of 10 separate cerebral hemisphere specimens were examined to define the surface topography of sulci and gyri, with attention to the appearance and anatomical patterns and variations of the collateral sulcus and the surrounding gyri.

RESULTS: The retrosigmoid approach allowed for clear visualization of the basal occipitotemporal surface. The collateral sulcus was identified and permitted easy endoscopic access to the ventricular atrium. The conical corridor thus obtained provided an average base working area of 3.9 cm2 at an average depth of 4.5 cm. The mean cortical thickness traversed to enter the ventricle was 1.4 cm. The intraventricular anatomy of the ipsilateral ventricle was defined clearly in all 8 exposures in this manner. The anatomy of the basal occipitotemporal surface, observed in a total of 18 hemispheres, showed a consistent pattern, with the collateral sulcus abutted by the parahippocampal gyrus medially, and the fusiform and lingual gyrus laterally. The collateral sulcus was found to be caudally bifurcated in 14 of the 18 specimens.

CONCLUSIONS: The retrosigmoid supracerebellar transtentorial transcollateral sulcus approach is technically feasible. This approach has the potential advantage of providing a short and direct path to the atrium, hence avoiding violation of deep neurovascular structures and preserving eloquent areas. Although this approach appears unconventional, it may provide a minimally invasive option for the surgical management of selected lesions within the atrium of the lateral ventricle.

 

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