Precise Localization of the Posterior Clinoid Process in the Fetal Skull Base

Objective: To determine the precise position of the posterior clinoid process (PCP) in fetuses. Materials and Methods: Skull bases of 32 fetuses (11 males/21 females) aged 17 to 32 weeks in utero were included in the study. The distances of PCP to certain reference points were measured. Results: The distances of PCP to the foramen ovale, foramen rotundum, superior orbital fissure, anterior clinoid process, foramen magnum, and crista galli were measured as 7.70±1.86 mm, 6.99±1.65 mm, 6.07±1.85 mm, 3.85±1.10 mm, 15.34±3.38 mm, and 14.49±2.65 mm, respectively. All parameters were similar for both sides ( P >0.05). Apart from the distance of PCP to the foramen magnum, the remaining parameters were similar for both genders. This parameter was greater in males than females ( P =0.001). All parameters were greater in the third-trimester fetuses than the second-trimester fetuses. All parameters increased with advancing gestational weeks ( P <0.001). Linear functions were calculated for the distances of PCP to the crista galli ( y = 1.311 + 0.551 × age), to the foramen magnum ( y = 0.086 + 0.638 × age), to the anterior clinoid process ( y = −0.303 + 0.174 × age), to the superior orbital fissure ( y = − 2.013 + 0.338 × age), to the foramen rotundum ( y = 1.803 + 0.217 × age), and to the foramen ovale ( y = 0.760 + 0.290 × age). Conclusion: The measured distances increased with growth. The linear functions displaying the growth dynamics of PCP-related parameters may be used to estimate the distances.