Anatomical Study of Pterygoalar and Pterygospinous Foramina

Abstract

Abstract Purpose: Pterygoalar bar (PTAB) is a bony bridge formed by the incomplete or complete ossification of the pterygoalar ligament extending between the lateral pterygoid lamina (LPL) and the greater wing of the sphenoid bone. Complete ossification of the pterygoalar ligament results in the formation of the so called “pterygoalar foramen” (PTAF), or Hyrtl’s foramen. On the other hand, pterygospinous bar (PTSB) is another bony bridge resulting from incomplete or complete ossification of the pterygospinous ligament, which extends from the pterygospinous process of the LPL to sphenoidal spine. Complete ossification of this ligament forms the pterygospinous foramen (PTSF), or the Civinini’s foramen. This study was undertaken to examine detailed anatomy and incidence of PTAB, PTSB and the corresponding foramina, as well as to establish their relationship with foramen ovale (FO). Methods: A total of 152 dry adult human skulls (304 sides) obtained from the collection of the Anatomy Department of Dokuz Eylül University were examined in terms of the presence/absence of PTAB/PTSB, their incidence and side, degree of ossification (complete/incomplete), and their relationship with FO. The distance between the spinous processes was measured in cases with incomplete ossification of PTAB/PTSB, while a digital caliper with 0.01 mm sensitivity (Mitutoyo, Japan) was used to measure horizontal and vertical diameters of the foramina in cases with complete ossification (i.e., when PTAF and PTSF were present). SPSS 22.0 statistical software was used for statistical analysis with Student’s t test and Pearson’s correlation analysis. The level of significance was set at p < 0.05. Results: Of the 152 skulls, 11 (7.23%) harbored PTAF and 2 harbored PTSF (1.3%). An incomplete PTAB or incomplete PTSB was present in 110/304 (33.4%) and 21/304 (6.9%) of the sides examined, respectively. PTAB was located medial, lateral, inferior, inferolateral, and inferomedial to FO in 15 (4.93), 29 (9.53%), 77 (25.32%), 28 (9.21%), and 3 (0.98%) of the sides. The distance between PTAB and FO was 7.43 ± 2.58 mm on the right, and 7.51 ± 2.50 mm on the left. The distance between two PTABs was 10.43 ± 3.65 mm on the right and 10.29 ± 3.30 mm on the left. The vertical diameter of PTAF was 3.80 ± 2.08 mm, and the horizontal diameter was 4.96 ± 2.24. In the presence of a foramen, the mean thickness of PTAB was 2.27 ± 0.74 mm, the mean width was 3.45 ± 3.40 mm, and the mean length was 6.54 ± 3.64 mm. No significant differences were identified between right and left-sided measurements (p > 0.05). Conclusion: Close adjacency of PTAB/PTSB to FO as well as their ability to form foramina may hamper the procedures requiring placement of transcutaneous needles into FO or may present anatomical challenges in surgery involving the base of the cranium. Owing to the possibility of neural compression, they may also have clinical significance for craniofacial neurosurgeons, anesthesiologists, radiologists, and dental surgeons. Our results may provide some anatomical insights for planning infratemporal fossa surgery.