Development and cross-sectional morphology of the recurrent laryngeal nerves in human fetuses

The recurrent laryngeal nerve is a bilateral branch of the vagus nerve that is mainly associated with the motorinnervation of the intrinsic muscles of the larynx. Despite its bilateral distribution, the right and left recurrent laryngealnerves display unequal length due to embryological processes related to the development of the aortic arches. This lengthasymmetry leads to theories about morphological compensations to provide symmetrical functions to the intrinsic musclesof the larynx. In this study we investigated the developmental and cross-sectional morphometrics of the recurrent laryngealnerves in human fetuses. Fifteen stillbirth fetuses donated to anatomical and medical research were used for investigation. Fetuses had intrauterine age ranging from 30 to 40 weeks estimated by biometry methods. Specialized anatomical dissectionof the visceral block of the neck was performed to prepare histological samples of the recurrent laryngeal nerves in its point ofcontact with the larynx, and morpho-quantitative techniques were applied to evaluate the epineurium and perineural space ofthe recurrent laryngeal nerves. No statistical difference in the cross-sectional morphology of the epineurium and perineuralspace between right and left recurrent laryngeal nerves intra-individually was confirmed, however, we found evidence thatthese structures are under greater development in the left recurrent laryngeal nerve during 30 to 40 weeks of intrauterinelife. Our data suggest that the nerves are under morphological development that possibly set the stage for accommodation oflarger diameter and myelinization of the left recurrent laryngeal nerve during post-natal life.