Anatomical Evaluation of Cavernous Sinus, Middle Fossa, and Paraclival Triangles of Fetal Skull Base During the Second Trimester.

The development of the skull base during the fetal period is critical, as the configuration of the cavernous sinus, middle fossa, and paraclival triangles forms the basis for future neurovascular relationships relevant to skull base surgery. Despite their clinical importance, normative morphometric data for these regions during the second trimester are limited. This study aimed to characterize the anatomical organization of fetal skull base triangles and to evaluate whether their proportional arrangement and bilateral symmetry are established prenatally. Second-trimester fetal specimens were examined using microsurgical dissection under operative microscopy. The cavernous sinus, middle fossa, and paraclival triangles were identified according to established classifications, and bilateral area measurements were obtained using a digital caliper. Intraobserver reliability was assessed by repeated measurements and Pearson correlation analysis. No significant differences were observed between the right and left sides (P>0.05), indicating preserved bilateral symmetry at this developmental stage. Within each side, a consistent hierarchical organization was evident, with clinoidal and oculomotor-related triangles occupying proportionally larger areas, while middle-fossa triangles were smaller. High intraobserver reliability was demonstrated across all measurements. These findings indicate that the proportional and hierarchical organization of skull base triangles is already established during the second trimester, suggesting that fundamental surgical corridors of the anterior and middle cranial base are present well before birth. This normative data set provides a foundation for future anatomical, embryological, and neurosurgical studies.