Emissary Foramina of the External Occipital Protuberance: A Magnetic Resonance Imaging Study

The posterior interparietal region is known to be a distinct area of the skull, predisposing to a variety of bony variants and congenital anomalies. The bony canals in this region have not yet been explored in detail. This study aimed to characterize them.

Overall, 82 patients underwent thin-slice contrast magnetic resonance imaging. Coronal and sagittal images were used for the analysis.

At the rostral limit of the posterior interparietal region, the parietal foramen (PF) and transmitting emissary vessels were identified in 84% of cases, mostly delineated as single channels. They were located in the left parasagittal region (PS) in 26%, lateral to the left PS in 33%, right PS in 40%, lateral to the right PS in 12%, and midline in 16% of the cases. In 4% of the cases, the PF presented an obstruction around the outer opening. In the more caudal part of the posterior interparietal region, 51% of the patients presented with fine bony canals and transmitting emissary vessels, lying in the midline and parasagittal levels.

The frequency of PFs may be underestimated for superficially hidden outer openings of the canals. The midline posterior interparietal region may present fine bony canals for transmitting emissary vessels that function complementarily with PFs.