The intracanalicular segment of the hypoglossal nerve: An anatomical study using magnetic resonance imaging

Few studies have documented the morphology of the intracanalicular segment of the hypoglossal nerve (CSHN). Therefore, the aim of this study was to characterize the CSHN using magnetic resonance imaging (MRI). In total, 95 patients underwent thin-sliced, contrast MRI. The axial and coronal images were used for analysis. The CSHNs were bilaterally identified in 97% and 94% of the 95 patients on the axial and serial coronal images, respectively. On axial images, length of the hypoglossal canal was measured as 8.2 ± 1.66 mm on the right and 8.4 ± 1.71 mm on the left. The CSHN was delineated as a slightly tortuous, linear structure with variable length. The CSHN course in the hypoglossal canal could be classified into the ventral, central, and ventrodorsal types, with the ventral type most predominant and found in 65% on the right side and 43% on the left. The angle formed by the CSHN and perpendicular line was highly variable. On serial coronal images, the CSHN course in the hypoglossal canal was also variable and could be found in the any part of the canal. The CSHN is a distinct structure characterized by morphological variability, which can influence the type of hypoglossal neuropathy arising from the CSHN.