Variation in Lingual Nerve Course: A Human Cadaveric Study

Abstract

The lingual nerve is a terminal branch of the mandibular nerve. It is varied in its course and in its relationship to the mandibular alveolar crest, submandibular duct and also the related muscles in the floor of the mouth. This study aims to understand the course of the lingual nerve from the molar area until its insertion into the tongue muscle. This cadaveric research involved the study of 14 hemi-mandibles and consisted of two parts: (i) obtaining morphometrical measurements of the lingual nerve to three landmarks on the alveolar ridge, and (b) understanding non-metrical or morphological appearance of its terminal branches inserting in the ventral surface of the tongue. The mean distance between the fourteen lingual nerves and the alveolar ridge was 12.36 mm, and they were located 12.03 mm from the lower border of the mandible. These distances were varied when near the first molar (M1), second molar (M2) and third molar (M3). The lingual nerve coursed on the floor of the mouth for approximately 25.43 mm before it deviated toward the tongue anywhere between the mesial of M1 and distal of M2. Thirteen lingual nerves were found to loop around the submandibular duct for an average distance of 6.92 mm (95% CI: 5.24 to 8.60 mm). Their looping occurred anywhere between the M2 and M3. In 76.9% of the cases the loop started around the M3 region and the majority (69.2%) of these looping ended at between the first and second molars and at the lingual developmental groove of the second molar. It gave out as many as 4 branches at its terminal end at the ventral surface of the tongue, with the presence of 2 branches being the most common pattern. An awareness of the variations of the lingual nerve is important to prevent any untoward complications or nerve injury and it is hoped that these findings will be useful for planning of surgical procedures related to the alveolar crest, submandibular gland/ duct and surrounding areas.

Revisiting the relationship between the submandibular duct, lingual nerve and hypoglossal nerve

“…Hölzle et al reported that SD runs deep in the floor of the oral cavity without a relationship with the LN in 11.8 % of the cases [12]. Al-Amery et al found that LN was passing below the SD before rising again toward the ventral surface of the tongue in 12 out of the 13 of the cases, in one case the relationship was similar with the findings of Hölzle et al [1,12,15].…”

“…They also found the mean distance between the LN and alveolar ridge was 12.36 mm and the mean distance between the LN and the lower border of mandible was 12.03 mm [1].…”

“…There is a wide variation in the course of LN up to its intersection with the SD. If the surgical procedures were performed without enough appreciation of the relationship between LN and SD, the damage potentiality to the LN will be increased as it is intertwined with the SD [1]. This study was limited by the number of the cadavers available so the findings may not possibly present the general population.…”

“…Most of the studies are describing a loop configuration of the lingual nerve (LN) around the submandibular duct (SD) [1,9,17]. They claim that the LN passes lateral to the SD, then continues superiorly and anteriorly on its medial side to the surface of hyoglossus [6,12].…”

“…It lies on the deep part of the submandibular gland and passes below the SD which crosses it from medial to lateral, then curves upward, forward and medially to enter the tongue. LN is the first key for the glandular excision by the endoscopic intraoral approach [1,8,16,19].…”