Anatomical and morphometric study of variations of the clivus in dried human skulls from the northeastern Thai population

Abstract

Purpose: Anatomical variations of the clivus may have clinical and embryological relevance but remain underexplored in specific populations. This study investigated the prevalence and morphometric characteristics of clival anatomical variants in dried human skulls from the Northeastern Thai population. Methods: Three hundred four dried human skulls (282 males, 22 females) were examined macroscopically. Variations of the clivus were identified and recorded by two independent observers, with discrepancies resolved by consensus. Descriptive statistics were used to report prevalence. Morphometric measurements (height and breadth) were taken for applicable variants using a digital caliper. Chi-square tests assessed sex differences. Results: Fossa navicularis magna and tubercle at the anterior margin of the foramen magnum were the most prevalent variants, each observed in 38 skulls (12.5%). The basilar processes were found in 12 skulls (3.9%), condylus tertius in 5 skulls (1.6%), and prebasioccipital arch in 1 skull (0.3%). These variations showed variable morphometry. Fossa navicularis magna averaged 5.1 mm in height and 4.1 mm in breadth; tubercle at the anterior margin of the foramen magnum, 2.7 mm in breadth; basilar processes, 3.9 mm in height; condylus tertius, 6.3 mm in height and 6.9 mm in breadth; and prebasioccipital arch, 10.5 mm in height and 15.5 mm in breadth. No significant sex differences were found for fossa navicularis magna (p = 0.40), tubercle at the anterior margin of foramen magnum (p = 0.61) or basilar process (p = 0.67). Conclusion: Clival variants, especially fossa navicularis magna and anterior tubercles, were found in 12.5% of skulls in this first study on Northeastern Thais. These may impact imaging interpretation and skull base surgery, reiterating the need for anatomical awareness in clinical contexts.