Morphometric and topographic analysis of calvaria: A special focus on parietal emissary foramina

Abstract

Background: The parietal foramina (PFs) are located on either side of the sagittal suture at the posterior aspect of the parietal bone. The part of the sagittal suture between the two PFs is called obelion because it resembles the Greek symbol % “obelos.” The PF transmits an emissary vein named Santorini vein which connects the extracranial veins to the superior sagittal sinus. The emissary veins are of clinical significance as they are involved in the pathway of spreading infection from the extracranial to the intracranial source. PF is of special interest to neuroanatomists and neurosurgeons due to its anatomical variations and surgical importance. Materials and Methods: A total of 111 dry human calvariae of unknown gender were included in the study. These human calvariae were observed for the presence or absence and also observed for the unilateral, bilateral, single, or multiple PFs. The foramina were macroscopically observed by using a magnifying lens, and a needle was probed into each foramen to check their patency. Topographical parameters were measured. Results: Out of 111 calvariae, a single parietal emissary foramen was observed in 63 (56.7%) on the right parietal bone, 67 (60.3%) on the left parietal bone, and absence of parietal emissary foramen on right parietal bone in 41 (36.9%) and 37 (33.3%) on the left parietal bone, bilateral absence in 23 (20.7%) of the parietal bones. The presence of parietal emissary foramen on the sagittal suture was observed in 2 (1.8%) of skulls and also noted the single, double, multiple PF in 56.7%, 2.7%, 1.8% and 60.3%, 4.5%, 0, respectively. The different shapes of PF that was observed were circle shape on the right side 69.3%, on the left 66.6%, slit shape on the right 0.9%, on the left 1.8%, oval shape on the right 2.7%, on the left 1.8%. Out of all parietal emissary foramen, bilateral PF was observed in 53 + single parietal foramen on right 63 + on left 67 + double on right 3 + on left 5 + multiple on right 3 = 247. Out of 247 PF, 8 were patent through and the connection was oblique. All the other foramina were found to open into the diploic space. For those foramina through and through patency could not be assessed. The distance between the PF, distance of PF and sagittal suture, distance from the bregma to obelion, distance from lambda to obelion were measured. The obtained results are tabulated. Conclusion: Parietal emissary veins are surgically important structures that receive little attention in scalp surgeries. These veins cause excessive bleeding if not located properly. The current study reports the anatomical variations in the PF which may serve as an important landmark to the neurosurgeon.