Regional Variation in Skull Thickness Along a Horizontal Plane: Implications for Neuroanatomy Teaching, Neurosurgery, Radiology and Forensic Analysis.

Objective To quantify skull thickness variation at a horizontal plane passing 2 cm above the highest points of the left and right supraorbital margins anteriorly and the external occipital protuberance posteriorly and to propose a standardized six-region classification for cranial margins. Methods Fifteen adult dry basilar skulls from four publicly funded medical institutions in Eastern India were studied. The skull margin at the defined plane was marked at 1-cm intervals between the anterior and posterior midlines on both sides. Thickness was measured using a digital micrometer by three independent observers, with mean values used for analysis. The margin was divided into six regions per side: anteromedial (AM), anterolateral (AL), lateral anterior (LA), lateral posterior (LP), posterolateral (PL), and posteromedial (PM). Inter-observer reliability was assessed using a two-way random-effects intraclass correlation coefficient (ICC). All statistical analyses were performed using Stata v18. Results A total of 2,235 measurements were analyzed. Thickness decreased from AM to LA regions and then increased toward the PM region. The LA region was thinnest (left=3.144±0.286 mm; right=3.234±0.809 mm), while the PM region was thickest (left=10.638±1.661 mm; right=11.266±1.659 mm). ICC exceeded 0.9 for over 80% of measurements, confirming high measurement consistency. Conclusions This study establishes a reproducible six-region classification and provides precise morphometric data along a clinically important horizontal plane. Apart from its use in cranium sectioning in cadavers, the findings can guide safe neurosurgical entry points, improve radiological lesion localization, and support forensic cranial analysis.