Subtemporal Approach and Its Infratentorial Extension: Review and a Comparative Analysis of Different Techniques

Introduction Surgical resection of lesions occupying the incisural space is challenging. In a comparative fashion, we aimed to describe the anatomy and surgical approaches to the tentorial incisura and to the rostral brainstem via the intradural subtemporal approach and its infratentorial extensions. Methods Six fresh human head specimens (12 sides) were prepared for the microscopic dissection of the tentorial incisura using the intradural subtemporal approach and its infratentorial extensions. Endoscope was used to examine the anatomy of the region inadequately exposed with the microscope. Image-guided navigation was used to confirm bony structures visualized around the petrous apex. Results Standard subtemporal approach provides surgical access to the supratentorial brainstem above the pontomesencephalic sulcus and to the lateral surface of the cerebral peduncle. The linear or triangular tentorial divisions can provide access to the infratentorial space below the pontomesencephalic sulcus. The triangular tentorial flap in comparison with the linear incision obstructs the exposure of anterior incisural space and of the prepontine cistern. Visualization of the brainstem below the trigeminal nerve can be achieved by the anterior petrosectomy. Conclusion Infratentorial extension of the intradural subtemporal approach is technically demanding due to critical neurovascular structures and a relatively narrow corridor. In-depth anatomical knowledge is essential for the selection of the appropriate operative approach and safe surgical resections of lesions.

Occipital transtentorial approach for pineal region lesions: Addressing the controversies in conventional teaching

Background: The occipital transtentorial (OT) approach is well-established approach for pineal region tumors and can be of choice for the lesions located around the suboccipital part of tentorium such as the quadrigeminal plate, posterior part of thalamus, tentorial surface of cerebellum, splenial region, posterior falx, and lesions around the tentorial incisura. However, it is not very much extensively used in the above-mentioned locations other than the pineal region. Methods: Thirty-one patients of pineal region lesions were operated by OT approach, the role of conventional preoperative evaluation of the anatomy of the venous sinuses, deep venous system, and tentorial angle was investigated. Results: A variety of lesions were operated using this approach achieving gross and near total resection in majority of the cases (76.6%), with acceptable postoperative mean modified Rankin scales (1.8). Conclusion: The OT is a preferable approach for pineal region lesions for patients of all ages and can be tailored for achieving high resectability rates irrespective of the status of the deep venous system and tentorial angle, with reasonable postoperative surgical outcome.

Perforating Arteries of the Lemniscal Trigone: A Microsurgical Neuroanatomic Description

Background: The perforating arteries in the dorsolateral zone of the midbrain play a crucial role in the functions of the brain stem. Their damage due to herniation, pathological lesions, or surgery, favored by the narrow tentorial incisura, can lead to hemorrhages or ischemia and subsequently to severe consequences for the patient.Objective: In literature, not much attention has been directed to the perforating arteries in the lemniscus; in fact, no reports on the perforators of this anatomical region are available. The present study aims to a detailed analysis of the microanatomy and the clinical implications of these perforators, in relation to the parent vessels. We focused on the small vessels that penetrate the midbrain's dorsolateral surface, known as lemniscal trigone, to understand better their microanatomy and their functional importance in the clinical practice during the microsurgical approach to this area.Methods: Eighty-seven alcohol-fixed cadaveric hemispheres (44 brains) without any pathological lesions provided the material for studying the perforating vessels and their origin around the dorsolateral midbrain using an operating microscope (OPMI 1 FC, Zeiss). Measurements of the perforators' distances, in relation to the parent vessels, were taken using a digital caliper.Results: An origin from the SCA could be found in 70.11% (61) and from the PCA in 27.58% (24) of the hemispheres. In one hemisphere, an origin from the posterior choroidal artery was found (4.54%). No perforating branches were discovered in 8.04% of specimens (7).Conclusion: The perforating arteries of the lemniscal trigone stem not only from the superior cerebellar artery (SCA), as described in the few studies available in literature, but also from the posterior cerebral artery (PCA). Therefore, special attention should be paid during surgery to spare those vessels and associated perforators. A comprehensive understanding of the lemniscal trigone's perforating arteries is vital to avoid infarction of the brainstem when treating midbrain tumors or vascular malformations.

Meningioma of posterolateral tentorial incisura: a case demonstration of paramedian supracerebellar transtentorial approach

The paramedian supracerebellar transtentorial approach allows unobstructed exposure to the quadrigeminal cistern, tectal plate, pineal region, tentorial incisura, medial basal temporal lobe, and posterior ambient cistern. The authors present a meningioma of the posterolateral tentorial incisura case in a 62-year-old male who presented with a long history of upper-extremity tremors and walking difficulties. MRI revealed supra- and infratentorial tumor extension and hydrocephalus. This approach enabled us to achieve gross-total resection without causing neurovascular injury or any postoperative neurological deficits. For each pathology, the pros and cons of various approaches should be considered based on the anatomy, vasculature, and any surrounding structures. The video can be found here: https://stream.cadmore.media/r10.3171/2021.4.FOCVID2138.

Interhemispheric Precuneus Retrosplenial Transfalcine Approach for Falcotentorial Meningiomas: Anatomic Study and Clinical Series

BACKGROUND Falcotentorial meningiomas are surgically challenging. Currently accepted approaches include occipital interhemispheric and supracerebellar infratentorial approaches, which have documented drawbacks. OBJECTIVE To propose an alternative approach to the posterior tentorial incisural space, the interhemispheric precuneus retrosplenial transfalcine approach (IPRTA). METHODS A total of 6 colored-silicone-injected adult cadaveric heads were dissected. We measured the interval between bridging veins and studied computed tomography venography scans of 20 subjects to confirm the feasibility of the IPRTA. Bony landmarks, the region's bridging veins, and the anterior and posterior borders of the approach were identified. The surgical corridor widths (veins’ interval) and lengths were compared between alternative midline approaches. We also reviewed 4 consecutive clinical cases using this approach. RESULTS The IPRTA provides the shortest distance to the anterior and posterior limits of the posterior tentorial incisura. Moreover, it is the only approach that provides direct visualization of the anterior and posterior limits of falcotentorial junction meningiomas. In all specimens and patients, a minimum 30-mm interval between the anterior and posterior parietal veins was found in at least one of the hemispheres. Tumor removal was successful in all 4 patients but resulted in mild paresthesia in the lower extremities of 2 patients and temporary foot drop in 1 patient. CONCLUSION The IPRTA offers the shortest and most direct corridor for falcotentorial meningiomas and provides excellent visualization of most of the critical structures in the region. Detailed preoperative evaluation of the deep and superficial venous structures is recommended.

A Study to Analyze the Tentorial Incisura in Indian Population, for Racial Differences and Its Impact in the Outcome of Patients with Head Injury

Aim To measure the size of tentorial notch in Indian population, compare it with the western population from the literature available, and analyze the relation between size of tentorial notch and the outcome in patients with head injury. Materials and Methods The study was done using 10 cadavers and 15 autopsy specimens. In all the specimens, tentorial incisura was measured using vernier caliper after opening the skull and cutting the midbrain at the level of tentorial edge carefully without damaging the tentorium. All measurements were done in millimeters. Results Mean values, age-dependent mean values, and percentile values were calculated for various parameters in the tentorial incisura. Majority of the tentorial incisura are of typical type. Cases of tentorial incisura are significantly smaller in the age group of 20 to 25 years. Rate of deterioration of Glasgow coma scale (GCS) is rapid when the tentorial incisura is large. Conclusion There were no significant variations in measurements of tentorial incisura in Indian population compared with the western population. Rate of deterioration of GCS is higher in patients who had large tentorial incisura compared with other groups, which is statistically significance. However, this is to be confirmed by further study using large groups of patients to be used for clinical applications.