Larynx

Cartilaginous framework and vocal cords

The larynx has a complex cartilaginous skeleton that keeps the airway open and supports the vocal apparatus. The organ is located on the cricoid cartilage (cricoid cartilage), the shape of which resembles a signet ring with a massive signet facing posteriorly. Superiorly lies the V-shaped thyroid cartilage (thyroid cartilage). It consists of two laminae that fuse anteriorly and remain open posteriorly. This cartilage protects the vocal folds and has superior and inferior horns, with the inferior horns articulating with the cricoid cartilage.

The paired arytenoid cartilages (arytenoid cartilages) rest upon the lamina of the cricoid cartilage and are also sheltered by the thyroid cartilage. Their anterior vocal processes give rise to the true vocal cords (vocal cords), which converge anteriorly to form the anterior commissure. The movements of the cords are controlled by intrinsic muscles: abduction is mediated by the posterior cricoarytenoid muscle, and adduction by the thyroarytenoid muscle.

An important protective element is the epiglottis (epiglottis). It attaches to the larynx at its stalk and to the hyoid bone via the hyoepiglottic ligament. During swallowing, the epiglottis tilts posteriorly, reliably sealing the laryngeal vestibule.

Laryngeal subdivisions, lymphatic drainage, and innervation

Anatomically, the larynx is divided into three key regions, which is of critical importance in oncology:

• Supraglottic region (supraglottis): extends from the tip of the epiglottis to the laryngeal ventricle. It possesses an extremely rich lymphatic network, with drainage directed to the upper and mid deep cervical nodes.
• Glottic region (glottis): encompasses the true vocal cords and extends to the lower border of the cricoid cartilage. Lymphatic drainage here is very sparse.
• Subglottic region (subglottis): also features sparse lymphatic drainage, directed toward the prelaryngeal, lower deep cervical, and paratracheal lymph nodes.

Innervation is provided by branches of the vagus nerve. The superior laryngeal nerve is responsible for sensation and the motor activity of only a single muscle—the cricothyroid. All other functions are mediated by the recurrent laryngeal nerve.

Diagnostic imaging of laryngeal squamous cell carcinoma

Squamous cell carcinoma accounts for the vast majority (98%) of all malignant laryngeal tumors. CT and MRI are used to assess tumor extent. The examination must be performed during quiet breathing, and axial slices are reconstructed strictly parallel to the true vocal cords.

The clinical and radiological presentation depends on the tumor location:

1. Glottic region (60%): detected early due to hoarseness. If the tumor remains confined to this region, lymph node metastases are rare.
2. Supraglottic region (30%): runs a covert course and is diagnosed late. Due to the abundant lymphatic network, half of patients already have regional metastases at the time of diagnosis. Infiltration of the pre-epiglottic fat space is frequently observed.
3. Subglottic region: isolated primary tumors here are exceedingly rare, typically resulting from the spread of disease from the glottic region.
4. Transglottic tumors: massively involve all three levels of the larynx.

Key criteria for staging on CT/MRI:

• Involvement of the anterior commissure (normally, the soft-tissue thickness there should not exceed 1 mm).
• Extension of tumor masses across the midline.
• Extension into the subglottic region (within the ring of the cricoid cartilage, there are normally no visible soft tissues).
• Involvement of the supraglottic region.
• Involvement of the base of the tongue (critically important for planning the extent of laryngectomy).
• Cartilage invasion (well visualized on tomograms, although ultrasound can detect early extralaryngeal spread).

Other pathologies of the larynx and trachea

In addition to squamous cell carcinoma, other pathological conditions may occur in the laryngeal region:

• Chondrosarcoma: a rare, slow-growing tumor typically originating from the cricoid cartilage. A specific sign on unenhanced CT is coarse "popcorn" calcification. It is treated by local resection.
• Adenoid cystic carcinoma: a tumor arising from minor salivary glands. It is characteristic of the subglottic space or tracheal walls and requires differential diagnosis when mass lesions are identified in these zones.
• Laryngocele: a cystic dilation of the laryngeal saccule (the laryngeal ventricle is a recess between the false and true cords). It can be internal (a smooth submucosal bulge in the supraglottic region) or external (extending into the neck through the thyrohyoid membrane along the superior laryngeal vessels). It is typically air-filled but may contain fluid. Important: when a laryngocele is identified, tumor obstruction of the ventricle must be ruled out.
• Vocal cord palsy: requires careful scanning of the recurrent laryngeal nerve along its entire course. On the left side, the nerve loops under the aortic arch, so the scanning zone must encompass the area from the medulla oblongata to the mediastinum. On the right side, the nerve loops under the subclavian artery and does not descend into the thoracic cavity, making a neck scan sufficient.

Thyroid and parathyroid glands: adjacent anatomy

The thyroid gland is located in the visceral compartment of the neck, lateral to the trachea, with its lobes connected by an isthmus. Embryologically, it descends from the foramen cecum of the tongue base. When this process is disrupted, an ectopic lingual thyroid is formed. A pyramidal lobe—a fibrous tissue band extending superiorly from the isthmus—is a frequent finding. Thyroglossal duct cysts, as remnants of embryonic development, present as midline neck masses that tend to enlarge following infections.

There are typically four parathyroid glands (less commonly up to six). They are located along the thymopharyngeal tract, most often posterior and inferior to the thyroid lobes, and can be found anywhere from the carotid bifurcation to the mediastinum. The primary imaging modality is ultrasound, often combined with fine-needle aspiration biopsy. Radioisotope diagnostics are used less frequently, having been largely replaced by antibody laboratory tests, and are primarily utilized to locate autonomous nodules in the setting of suppressed TSH or suspected thyroiditis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Anatomy of the pre-epiglottic and paralaryngeal fat spaces
• Ultrasonographic signs of extralaryngeal spread of laryngeal tumors
• Differential diagnosis of tracheal mass lesions
• Radiological anatomy of the thyropharyngeal tract and ectopic parathyroid glands
• Specifics of radioisotope studies (99mTc and I-123) in nodular goiter

Other topics in the Neuroimaging section

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