Thyroid Cartilage

1. Overview

The thyroid cartilage is the largest cartilage of the larynx and a prominent structure in the upper respiratory tract. It provides protection and structural support to the vocal cords and laryngeal cavity. Its external prominence, commonly referred to as the Adam’s apple, is more prominent in males due to the effects of androgens during puberty. The thyroid cartilage plays a crucial role in phonation, airway protection, and swallowing.

2. Location

The thyroid cartilage is located:

• In the anterior neck, below the hyoid bone

• Above the cricoid cartilage and in front of the larynx

• At the level of the C4–C5 vertebrae in most adults

It forms the anterior and lateral walls of the larynx and is situated just inferior to the thyrohyoid membrane and superior to the cricothyroid membrane.

3. Structure

The thyroid cartilage is composed of:

• Hyaline cartilage: Flexible but strong cartilage that can ossify with age

• Two laminae: Flat plates that join anteriorly to form the laryngeal prominence (Adam’s apple)

• Superior and inferior horns (cornua):

  • Superior horns attach to the hyoid bone via the thyrohyoid ligament

  • Inferior horns articulate with the cricoid cartilage at the cricothyroid joints

The thyroid cartilage has a thyroid notch at the superior border and a posterior edge that remains open to allow for movement of internal laryngeal structures. It serves as a key attachment point for muscles and membranes involved in voice production and swallowing.

4. Function

The thyroid cartilage performs several critical functions:

• Structural protection: Shields the vocal cords and the entrance to the trachea

• Anchorage point: Serves as a point of attachment for the vocal cords, intrinsic laryngeal muscles, and ligaments

• Voice modulation: Participates in changing pitch through tensioning of the vocal cords via the cricothyroid joint

• Supports airway patency: Maintains the open structure of the upper airway

5. Physiological Role(s)

The thyroid cartilage contributes to multiple respiratory and phonatory functions:

• Phonation: Movements at the cricothyroid joint tilt the thyroid cartilage, altering vocal cord tension and thereby pitch

• Air passage: Maintains the laryngeal opening to allow smooth passage of air during breathing

• Swallowing and airway protection: Coordinates with other laryngeal structures to prevent aspiration by elevating and closing the larynx during swallowing

6. Clinical Significance

Laryngeal Trauma

The thyroid cartilage can be fractured or displaced due to blunt neck trauma (e.g., in motor vehicle accidents, sports injuries, or strangulation). Symptoms include:

• Hoarseness

• Stridor

• Painful swallowing (odynophagia)

May require surgical repair if the airway is compromised.

Thyroplasty

A surgical procedure that involves implanting material into or manipulating the thyroid cartilage to reposition a paralyzed vocal cord. It’s used to improve voice quality in vocal cord paralysis (Type I thyroplasty).

Cricothyrotomy Landmark

The cricothyroid membrane, located just below the thyroid cartilage, is used in emergency airway access procedures like cricothyrotomy. The prominence of the thyroid cartilage helps identify this membrane quickly.

Laryngeal Cancer Involvement

Advanced tumors of the larynx may invade the thyroid cartilage, especially if arising from the glottis or subglottic regions. Invasion into cartilage is a key factor determining the need for total laryngectomy.

Ossification and Aging

The thyroid cartilage begins to ossify with age, particularly in males. On radiographs and CT scans, this can appear as calcified structures and may aid in age estimation during forensic investigations.

Adam’s Apple Prominence

The anterior laryngeal prominence is typically more prominent in males due to hormonal effects on cartilage growth during puberty. While not pathological, it can be a source of cosmetic concern for some individuals.