EMBRYOLOGY:
Its embryonic development occurs from the 4th week of gestation and is closely related to the development of the trachea. It comes from the ventral groove of the laryngotracheal groove that deepens forming a septum that separates the laryngotracheal tube from the esophagus.It is generated from the endoderm and mesenchyme adjacent to the primitive intestine between the 4th and 6th-gill arch. - The hypobranchial eminence will give origin to the epiglottis and the cuneiforms.- The 4th arch and 6th arch will give origin to the thyroid and cricoid respectively. (1)
Because they share a common embryonic origin, any congenital malformation of the esophagus will have a laryngeal or tracheal repercussion. (Fig. 1)
ANATOMY:
We will address the anatomic structures that the radiologist must be familiar with to be an effective consultant with the otolaryngologist. Laryngeal anatomy can be grouped into three elements:
- CARTILAGINOUS SKELETON.
- VOCAL CORDS.
- PARAGLOTTIC SPACES.
CARTILAGINOUS SKELETON:
- Thyroid: The largest of all the cartilages of the larynx, with shield morphology. It has two laminae that meet in the midline. The angle of fusion is 90 degrees forming an anterior projection known as Adam's apple. The laminae project posteriorly generating superior and inferior horns as the insertion site of the thyrohyoid ligament. (2) (Fig 2).
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- The inferior horn serves as an articular surface with the cricoid.
- Thyroid ligaments:
- Thyroepiglottic ligament: site of attachment of the epiglottis to the thyroid cartilage.
- Vestibular ligament: Also named false vocal cord. Just below the thyroepiglottic junction. It constitutes the superior border of the laryngeal vestibule.
- Vocal ligament: True vocal cord and responsible for voice generation and joins just inferior to the vestibular ligament. It joins the angle of junction between the thyrohyoid laminae below the vestibular fold. To join the vocal process of the arytenoid cartilage.
- Cricoid: The only complete cartilage of the airway and with ring morphology. (Fig. 3)
- Arytenoids: Located in the superior and lateral part of the edges of the lamina quadrigemina and pyramidal morphology. The vocal cords are inserted in the vocal process (anterior aspect) and the lateral aspect (muscular) where the posterior and lateral cricoarytenoid muscles are inserted. (2) (Fig 4).
- Corniculate and cuneiform: fibroelastic cartilage nodules at the apices of the arytenoids.
- Epiglottis: fibroelastic cartilage in the form of a leaf that projects behind the tongue and the hyoid bone, in its lower part is inserted the thyroepiglottic ligament and the aryepiglottic and glossoepiglottic folds forming the vallecula. (2) (Fig. 5)
VOCAL LIGAMENT AND VESTIBULE:
Two ligaments arise from the arytenoid towards the junction between the thyroid laminae. They are separated by a lateral sacculation called the laryngeal vestibule. The laryngeal vestibule corresponds to the anatomical boundary between the supraglottis and the glottis.The vocal ligament corresponds to a bilateral mucosal fold, composed of the thyroarytenoid muscle in its inner course from the thyroid lamina to the arytenoid cartilage.
PARAGLOTTIC SPACE:
An even space containing fat located between the cartilaginous skeleton and the mucosal surface of the larynx. At the level of the false vocal cord, this space is predominantly filled with fat. In the true vocal cord, the fat is thinned and only lateral to the thyrohyoid muscle. The importance of the paraglottic space lies in the fact that it is a site of dissemination of neoplastic disease and that it is not visible in nasofibrolaryngoscopy and therefore its evaluation in the diagnostic images is of vital importance. (2,6) (Fig 6)
PRE-EPIGLOTTIC SPACE:
Fat space anterior to the epiglottis of C-shaped morphology in axial images. Its posterior border corresponds to the epiglottis and anteriorly to the thyrohyoid membrane together with the thyroid laminae, inferiorly it continues with the paraglottic spaces. (2,6) (Fig 7)
DIVISION OF THE LARYNX:
The proper anatomy of the larynx is divided into three sectors, each with its own boundaries: Supraglottis (Fig 8), Glottis (Fig 9), Subglottis (Fig 10).
- Intrinsic laryngeal muscles: The ability to generate vocal sound is secondary to the contraction and relaxation of the vocal folds by the articulation of the arytenoid cartilages and glottic intrinsic laryngeal muscles innervated by the recurrent laryngeal nerve (except for the cricothyroid muscle). (Fig 11)
LARYNGEAL TRAUMA:
Laryngeal trauma, whether traumatic or penetrating, is a life-threatening injury in that it closely affects airway patency and has an incidence in Europe of between 1:5000 to 1:137,000. Laryngeal trauma includes soft tissue injury, cartilage fractures, laryngotracheal sections, and laryngeal stenosis. (3,4)
- SOFT TISSUES: It may even be the only sign of trauma. As the larynx is richly vascularized and has abundant connective tissue, it is prone to hematoma formation and submucosal edema that can close the glottis.
- It is very important to evaluate the symmetry of the soft tissues.
- They should be suspected when a hematoma is visualized or there's bulging of the vocal cords. Laryngeal edema is usually symmetrical and laryngeal lacerations should be suspected with the presence of air within the paraglottic space. (3,4) (Fig. 12, 13, 14)
- FRACTURES AND DISLOCATIONS OF THE LARYNGEAL SKELETON: They are quite difficult to see due to their contours and irregular ossification. They can be horizontal, vertical, or oblique discontinuities.
- Fractures of the thyroid are the most common and generated by anteroposterior compression and generate paramedian fracture of the thyroid wings. While strangulation is caused by compression of the larynx on the cervical spine. (Fig 15, 16)
- Cricoid fractures require extreme force and are usually associated with hematomas. Cricoid fractures are RARE to be isolated and are related more to fractures of other associated cartilages. In 50% of the cases, it is with laryngotracheal separations. In complete sections, the trachea descends to the mediastinum. (3,4) (Fig 17, 18)
INFECTIONS OF THE LARYNX:
EPIGLOTTITIS:
Acute infection affects the supraglottis. The most causative agent is Haemophilus influenza, streptococcus, candida, and viruses can generate it.
Occurs between 2 and 4 years of age, the newborn is protected by the mother's vertical immunity but resolves within three months after birth. Fever and signs of respiratory obstruction such as sniffing position to move the epiglottis away from the airway and salivation with respiratory stridor. Radiologic findings include Increased size of the epiglottis, which is up to two to three times enlarged. (5) (Fig. 19)
CROUP (LARYNGOTRACHEITIS):
Most common disease of the pediatric larynx and occurs between 1 and 3 years of age. it is a viral infection by parainfluenza 1 and 3, RSV, and influenza. There is diffuse mucosal edema in the subglottis and trachea. The subglottis is the narrowest area of the larynx in pediatrics and the subglottis is the only site in the entire larynx that is covered in 360 degrees of cartilage. Therefore, subglottic laryngeal edema must be treated with great care because of airway compromise. The diagnosis is clinical, but the radiography is intended to rule out other causes of stridor such as the presence of foreign bodies. (5) (Fig. 20)
SQUAMOUS CELL TUMOR OF THE LARYNX:
The most common malignant neoplasia of the neck. It is more common in men than in females (3:1). Risks factors include Alcoholism, smoking, and viral infections such as HPV. Normally its origin is from de laryngeal mucosa and extends to the submucosa. The diagnosis is made by laryngoscopy and diagnostic imaging. Most of the cases originate from the glottis (Fig 21, 22)(65%), followed by supraglottis (Fig 23, 24)(30%) and subglottis (Fig 25, 26)(5%).
Squamous cell tumor of the larynx has four classical imaging patterns: 1. Abnormal enhancement, 2. Soft tissue thickening, 3. Exofitic mass and 4. Combination of the three previous.
What should the radiology report contain?
- Location of the mass (Supraglottis, Glottis, Subglottis)
- Invasion of the pre-epiglottic and paraglottic spaces
- Describe transglottic extension
- Compromise of the cartilaginous skeleton
- Metastasis (Nodal and extraglottic).