Case-based analysis to assess the validity of the Hat Brim Line Rule in cranial trauma

This study aims to evaluate the forensic reliability of the Hat Brim Line Rule (HBL Rule) in differentiating between accidental falls and intentionally inflicted blunt head trauma. Given the frequent diagnostic ambiguity in cranial injuries, particularly in forensic autopsies, the HBL Rule offers a potentially useful anatomical reference point for assessing the origin of skull fractures. A retrospective analysis was conducted on 78 anonymized autopsy reports from the digital archive of the Institute of Legal Medicine in Berlin, spanning from 2008 to 2024. Each case was classified based on the trauma dynamics (fall from <2 m, fall from stairs, fall from >2 m, or inflicted trauma) and analyzed for fracture location relative to three anatomical landmarks: Above G Line, Hat Brim Line (HBL), and Below External Auditory Meatus (EAM). Statistical associations were calculated using descriptive analysis and chi-square tests to compute the p-value. Fractures located below the EAM were significantly more frequent in inflicted trauma cases, in contrast with the HBL rule. Falls from heights tended to involve fractures above the G Line, while staircase falls often produced complex, multi-regional injuries. The HBL area was involved in most cases across all trauma dynamics but was not exclusively associated with a specific etiology. The hat brim line rule may serve as a useful auxiliary tool in the differential diagnosis of cranial trauma, but it cannot be used independently to distinguish between accidental and inflicted injuries. Its use should be integrated within a multidisciplinary framework, combining anatomical findings, contextual data, and advanced statistical or computational methods to improve diagnostic accuracy.