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Vagus nerve (Cranial nerve X)

The vagus nerve (cranial nerve X) is the longest cranial nerve, extending from the brainstem through the neck and thorax into the abdomen. It is a mixed nerve with both sensory and motor components, playing a crucial role in autonomic control of the heart, lungs, and digestive tract. Its widespread distribution and vital regulatory functions make it a key structure in both clinical neurology and radiology.

Synonyms:

  • Cranial Nerve X

  • CN X

  • Pneumogastric nerve

  • Nervus vagus

Function:

  • Provides parasympathetic innervation to thoracic and abdominal organs (heart, lungs, digestive tract up to the splenic flexure).

  • Conveys sensory information from the pharynx, larynx, external ear, and viscera.

  • Controls motor functions of the soft palate, pharynx, larynx, and parts of the esophagus (important for swallowing and speech).

  • Modulates heart rate, gastrointestinal peristalsis, sweating, and some muscle movements in the mouth, including speech (via recurrent laryngeal nerve branch).

MRI Appearance:

  • 3D T2-weighted MRI:

    • The vagus nerve appears as a small, round, hypointense (dark) structure within the carotid sheath, typically posterolateral to the carotid artery and anterolateral to the internal jugular vein.

    • 3D high-resolution T2 sequences (e.g., CISS, FIESTA, SPACE) are best for nerve visualization.

    • It can be traced from the medulla oblongata through the jugular foramen, along its course in the neck, and into the thorax.

  • T1-weighted MRI:

    • The vagus nerve is generally isointense to slightly hypointense compared to adjacent muscle tissue.

    • Its distinction from surrounding structures is less conspicuous than on T2, but can be appreciated in high-resolution images or with the use of contrast.

CT Appearance:

  • The vagus nerve is not well visualized on conventional CT due to its small size and soft-tissue density.

  • Occasionally, it may be inferred by its anatomical position within the carotid sheath between the internal jugular vein and the carotid artery.

  • CT Angiography: The nerve is identified indirectly by recognizing adjacent vascular landmarks or when affected by pathological enlargement (e.g., schwannomas).

  • CT is primarily useful for evaluating secondary effects (masses, schwannomas, or trauma) rather than direct visualization of the nerve.

MRI images

Vagus nerve (Cranial nerve X) MRI 3T axial image 1

MRI images

Vagus nerve (Cranial nerve X) MRI 3T axial image