Anatomical variability of the hypoglossal dural pori and canal: double hypoglossal dural porus is the main anatomical configuration in the German population

The hypoglossal nerve innervates all the extrinsic and intrinsic tongue muscles except the palatoglossus. Hypoglossal rootlets emerge from the brainstem via the pre-olivary sulcus, fuse to fiber bundles which pierce the cranial dura mater, and leave the skull through the hypoglossal canal. While the presence of two hypoglossal fiber bundles piercing the dura separately, as well as the presence of exostoses in the hypoglossal canal are well known phenomena, their co-occurrence and the prevalence of these variations in the German population has poorly been described. 101 formaldehyde fixated skull base sides (52 right, 49 left) from the collection of the Institute of Anatomy Mainz, Germany, were used in this study. The course of the hypoglossal nerve from the dural porus to the entrance in the hypoglossal canal was investigated by macroscopical dissection. In 32.7% (n = 33) only one dural porus on each side was present. In most cases (65.3%, n = 66) two hypoglossal dural pori were visible and in 2% (n = 2) three dural pori. Five types of hypoglossal canal configuration could be distinguished: Type 1: Simple canal (34.7%); Type 2: Exostosis at the superior margin (superior lingula, 31.7%); Type 3: Exostosis at the inferior margin (inferior lingula, 4%); Type 4: Both a superior and an inferior lingula (3%); Type 5: Complete osseus bridge (26.7%). Additionally, we described a rare case of a triplication of the hypoglossal canal. A double hypoglossal dural porus is the most common anatomical configuration in the German population.