Anatomy: Reccurent Laryngeal Nerve
Vagus Nerve: The reccurent laryngeal nerve is a branch of the vagus nerve so an understanding of the vagus nerve is needed to understand its branches. The vagus nerve (Cranial Nerve X) is a mixed cranial nerve with motor, sensory, special visceral and autonomic functions. It is the longest cranial nerve in the body but also has a large and complicated territory of innervated end organs. Branches of the vagus nerve innervate the muscles of the larynx and pharynx, sensation of the external tympanic membrane and portions of the ear, special taste sensation from the root of the tongue and epiglottis, and the innervation of the parasympathetic cardiovascular and gastrointestinal systems. After it exits from the skull base via the jugular foramen, the vagus nerve then courses through the carotid sheath posterior to the carotid artery and internal jugular vein. This anatomy, while variable, variable giving off several branches during its descent including the auricular branch to the ear, pharyngeal branches to the pharyngeal plexus, the superior laryngeal nerve (with external and internal branches), cardiac branches, and finally the recurrent laryngeal nerve.
Reccurent Laryngeal Nerve: The recurrent laryngeal nerve has a distinct course on each side. On the right, it branches from the vagus anterior to the subclavian artery, loops posteriorly around it, and ascends into the tracheoesophageal groove. On the left, it branches anterior to the aortic arch, looping posterior to the ligamentum arteriosum and arch before ascending in the same tracheoesophageal groove. Both sides enter the larynx deep into the inferior constrictor at the level of the cricothyroid joint. The recurrent laryngeal nerve provides motor innervation to all intrinsic laryngeal muscles except the cricothyroid muscle and sensory innervation to the mucosa below the vocal folds, cervical trachea, and upper esophagus. Anatomic variations include a non-recurrent RLN, most often right sided and associated with an aberrant right subclavian artery, as well as frequent extralaryngeal branching.
Clincal Relevance:
Surgery: From a surgical perspective, the recurrent laryngeal nerve is highly vulnerable during thyroidectomy, parathyroidectomy, central neck dissection, tracheostomy, esophagectomy, anterior cervical spine surgery, and cardiothoracic procedures involving the aortic arch. Similarly, placement of vagus nerve simulators require knowledge of the vagus nerve within the carotid sheath. Surgical injury can result in ipsilateral vocal fold paralysis causing hoarseness, dysphonia, aspiration risk, or, if bilateral, airway obstruction. Recognizing the anatomical course, common variants, and associated radiologic changes is essential for preoperative planning, intraoperative nerve preservation, and postoperative assessment
Radiology: Radiographically, the recurrent laryngeal nerve itself is rarely directly visualized but its course can be inferred at its branch points and within the tracheoesophageal groove. Pathologic processes such as tumor, infection, or postsurgical changes can obscure fat planes or distort this region on corss sectional imaging. Imaging signs of unilateral vocal cord paralysis include medial deviation and thickening of the ipsilateral aryepiglottic fold, dilation of the ipsilateral piriform sinus, anteromedial rotation of the arytenoid cartilage, and enlargement of the laryngeal ventricle. If there is clincal concern for new onset vocal cord paralysis it is important that cross sectional imaging protocols extdnign inferiorly below the artic arch to cover the entire course of the nerves course. On the left, the RLN is particularly susceptible to compression by mediastinal masses, aortic aneurysms, or pulmonary artery enlargement; on the right, subclavian artery aneurysms or apical lung tumors may cause similar deficits.
