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Left recurrent laryngeal nerve

The left recurrent laryngeal nerve (RLN) is a major branch of the vagus nerve (cranial nerve X). Unlike the right RLN, which loops around the subclavian artery, the left RLN arises from the vagus nerve in the thorax. It loops under the arch of the aorta, posterior to the ligamentum arteriosum, before ascending superiorly in the tracheoesophageal groove toward the larynx.

Along its course, the left RLN gives motor, sensory, and autonomic branches. It enters the larynx below the inferior pharyngeal constrictor muscle, deep to the inferior cornu of the thyroid cartilage. The nerve is closely related to the thyroid gland, trachea, and esophagus, making it particularly vulnerable during thyroid, parathyroid, cardiac, and mediastinal surgeries.

Clinically, injury to the left RLN can result in unilateral vocal cord paralysis, leading to hoarseness, dysphonia, aspiration risk, and impaired airway protection. Compression by mediastinal masses, aortic aneurysms, or enlarged left atrium (Ortner’s syndrome) can also damage the nerve.

Synonyms

  • Inferior laryngeal nerve (after entering larynx)

  • Branch of vagus nerve (CN X)

Function

  • Provides motor innervation to all intrinsic laryngeal muscles except the cricothyroid (supplied by external branch of superior laryngeal nerve)

  • Provides sensory innervation to mucosa of the larynx below the vocal cords, trachea, and cervical esophagus

  • Coordinates phonation, swallowing, and airway protection

MRI Appearance

T1-weighted images:

  • Difficult to visualize directly due to small caliber

  • Seen as a linear hypointense structure within the tracheoesophageal groove

  • Indirect signs: muscle denervation (atrophy, fatty infiltration) in laryngeal muscles

T2-weighted images:

  • Appears as a thin hypointense nerve relative to surrounding soft tissue

  • Denervation edema in intrinsic laryngeal muscles shows hyperintensity

STIR:

  • Suppresses fat, improving contrast between the nerve and surrounding structures

  • Sensitive for inflammatory or infiltrative changes

T1 Post-Gadolinium (Gd-enhanced MRI):

  • The nerve itself may not enhance significantly

  • Enhancement may be seen in cases of neuritis, perineural tumor spread, or postoperative scarring

  • Indirect evaluation: abnormal enhancement of denervated laryngeal muscles

MRI Non-Contrast 3D Imaging:

  • Provides high-resolution mapping of the tracheoesophageal groove and laryngeal framework

  • Useful in surgical and oncologic planning for thyroid cancer, mediastinal tumors, and laryngeal preservation

CT Appearance

Non-contrast CT:

  • Nerve itself is not usually visualized due to small caliber

  • Indirect signs: asymmetry of laryngeal ventricles or vocal cord position in RLN palsy

CT Post-Contrast:

  • Helpful for identifying extrinsic compression or displacement by tumors, lymphadenopathy, or vascular structures (aortic arch, left atrium)

  • Detects causes of RLN palsy such as thyroid carcinoma, esophageal tumors, mediastinal masses, or aortic aneurysm

  • 3D reconstructions useful in evaluating relationship to thyroid gland and mediastinal structures

MRI image

Left recurrent laryngeal nerve MRI axial image -img-00000-00000

CT image

Left recurrent laryngeal nerve ct axial image -img-00000-00000