The Tentorial Notch: Morphometric Analysis and its Clinical Relevance to Neurosurgery

Abstract

Introduction: The tentorial aperture is a complex space that varies considerably in size and shape. Although this space is defined by the free edges of the tentorium cerebelli, it has remained anatomically elusive. Modern neuroimaging methods routinely provide images of the tentorial notch but the literature so far available is remarkably devoid of extensive observations on the different types of tentorial notches. Dimensions of tentorial notch may determine the clinical sequelae and prognosis of many neurological conditions. Aim: To analyse the anatomical variations of tentorial notch, elucidating its clinical relevance in neurosurgery. Materials and Methods: A descriptive cross-sectional study was performed from August 2010-January2012. The midbrain was sectioned in an axial plane following the contour of the tentorial edge during medico-legal autopsies in 40 adult human cadavers, age ranging from 20 to 65 years. The parameters measured were: 1) Anterior Notch Width (ANW), the width of tentorial notch through the posterior aspect of the dorsum sellae; 2) Maximum Notch Width (MNW), the maximum width of the tentorial notch in axial plane; 3) Notch Length (NL), the distance between posterosuperior edge of the dorsum sellae in the mid-plane and the apex of notch; 4) Interpedunculoclival (IC) distance, the distance from the interpeduncular fossa to the posterosuperior edge of the dorsum sellae; 5) Apicotectal (AT) distance, the distance between the tectum of midbrain in the mid-plane and the apex of tentorial notch. The data obtained was analysed using Statistical Package for the Social Sciences (SPSS) version 21.0. Results: The quartile groups defined by MNW (mean 29.77±2.26 mm) were labeled as narrow, midrange and wide. Quartile groups defined by NL (mean 57.98±4.52 mm) were labeled as short, midrange and long. By combining these six groups into matrix formation, tentorial notches were classified into eight types. Applying quartile distribution technique to IC (mean 21.21±3.72 mm), brainstem positions within the tentorial notch were labeled as prefixed, midposition and postfixed. Conclusion: Variations in the dimensions of tentorial aperture may be implicated in the different clinical presentations related to transtentorial herniation, concussion and acceleration-deceleration injuries. The results of the present study provide a baseline data about tentorial notch which may facilitate neurosurgical decision making.