[Variations in the course of the inferior laryngeal nerve. Surgical anatomy, classification, diagnosis]

Because of multiple variations in course, the inferior laryngeal nerve shows a great variety of topographic relations to adjacent cervical structures. It may recur in the tracheoesophageal groove or anteriorly or posteriorly to it. It can pass under, over, or through the ramifications of the inferior thyroid artery. If Zuckerkandl's tubercle is enlarged, the nerve may be luxated. It is firmly fixed to the ligament of Berry by tight adhesions. Before entering the larynx, the nerve may show multiple ramifications. It may also recur around the inferior thyroid or vertebral artery. On the right, a nonrecurrent nerve is found in 0.6-0.8% of individuals, always in coincidence with a "lusorian" artery. Three course variations can be distinguished: descending (type I), horizontal (II), and ascending (III). A nonrecurrent nerve on the left is extremely rare, as it can only be found as a combination anomaly of a right-sided lusorian artery with situs inversus viscerum. The divided inferior laryngeal nerve shows recurrent and nonrecurrent ramifications. A nonrecurrent inferior laryngeal nerve can be indirectly ruled out preoperatively by demonstration of a normally developed brachiocephalic trunk via colour-coded duplex ultrasound.