The nasopharynx is the most superior part of the pharynx, more closely related to the nasal cavities than the oropharynx or laryngopharynx.
Structure
Macroscopic Appearance
The nasopharynx is a non-collapsible tube, sited above the soft palate and posterior to the nasal cavity.
The roof of the nasopharynx curves inferiorly as it progresses posteriorly, and is continuous with the posterior wall of the oropharynx. The anterior aspect is formed by the body of the sphenoid bone, and the curved posterior aspect by the basilar part of the occipital bone. The most postero-inferior part of the nasopharynx is separated from the anterior arch of the atlas by the pharyngobasilar fascia and the superior constrictor muscle. The roof contains the pharyngeal tonsil (adenoid).
The lateral walls of the nasopharynx contain the opening of the pharyngotympanic tube. The cartilage of this tube causes the mucosa to bulge, forming the tubal elevation. The tubal tonsil lies just posterior to the elevation, and two folds (the salpingopharyngeal and more anterior salpingopalatine folds) pass inferiorly from the tubal elevation to the pharynx and soft palate respectively. Behind the tubal tonsil is the pharyngeal recess.
The floor of the nasopharynx formed by the nasal surface of the soft palate. The floor is the only mobile part of the nasopharynx.
The nasopharynx communicates with the nasal cavity through the paired nasal apertures, and with the oropharynx through the pharyngeal isthmus.
Microscopic Appearance
The epithelium of the nasopharynx is of respiratory type (ciliated pseudostratified columnar with goblet cells) near the nasal cavities and non-keratinising stratified squamous type near the pharyngeal isthmus. Numerous submucosal and mucosal glands open onto the mucosal surface.
The junction between the two cell types is noted for columnar cells with villi (not cilia). This zone extends from the superior tip of the nasal septum, to the pharyngotympanic tubes, and finally to the union of the soft palate with the lateral walls of the pharynx.
Physiological variations in structure
During swalloing, the posterior part of the soft palate elevates and closes the pharyngeal isthmus.
In childhood, the pharyngeal tonsil is relatively large compared to the nasopharynx, and may lead to difficulties with nasal breathing. It begins to involute by the age of 8 – 10, usually negating this problem.
Pathological variations in structure
Adenoidectomy refers to the removal of the pharyngeal tonsil. It is performed when a large pharyngeal tonsil is causing obstruction of the nasopharynx or pharyngotympanic tubes.
Neurovascular Supply
Arterial Supply
The nasopharynx receives arterial supply from branches of the external carotid artery. The primary vessels include the ascending pharyngeal artery (lateral walls), ascending palatine artery (region around pharyngotympanic tube, soft palate), and the greater palatine artery and artery of the pterygoid canal which supply the roof.
Venous drainage
Veins form a plexus beneath the constrictor muscles, typically draining to the pterygoid plexus of veins. Some blood may empty directly into the internal jugular vein.
Lymphatic drainage
Three distinct pathways of lymphatic drainage from the nasopharynx exist:
- Posteroinferiorly to the retropharyngeal nodes (including the node of Rouvierre), and from there to upper deep cervical nodes.
- Directly to superior deep cervical nodes
- Laterally to mastoid and spinal accessory nodes (region V)
Innervation
Sensory supply is predominately visceral through the pharyngeal plexus of nerves. The main contributor is the glossopharyngeal nerve (IX). A small section of the anterior medial roof of the nasopharynx is supplied by somatic sensory branches of the maxillary nerve (V2).
Motor supply to the muscles of the nasopharynx is via the vagus nerve (X) except for tensor veli palatini, which receives motor input from the mandibular nerve (V3).
Routes of cancer spread
Nasopharyngeal cancer may develop extensive local invasion and distant metastasis.
Local Invasion
Nasopharyngeal cancers may spread easily through any of the nearby foramen / spaces between skull bones. These include:
- Foramen ovale (mandibular division of trigeminal nerve)
- Foramen spinosum (meningeal branch of V3, middle meningeal artery)
- Foramen lacerum / carotid canal
- Jugalar foramen (transmitting the internal jugular vein, IX, X and XI)
The foramen ovale and foramen lacerum are particularly close to the nasopharynx.
If invading through the bone, cancer may spread:
- Anteriorly into the nasal cavities (87%)
- Anterosuperiorly into the cavernous sinus (19%) or orbit (4%)
- Laterally into the pharyngotympanic tube, leading to obstruction and otitis media, or into the pterygoid muscles leading to jaw dysfunction (50%).
- Posteriorly into the occipital bone / clivus (41%) or prevertebral muscles (19%)
- Superiorly into the sphenoid bone (38%) and sinus, and the pituitary gland (3%), cavernous sinus, and optic chiasm
- Inferiorly into the soft palate and oropharynx (21%)
Lymphatic spread
A plexus of submucosal lymphatics exists beneath the entire pharynx, including the nasopharynx. Lymph may follow three pathways, to retropharyngeal nodes, directly to superior deep cervical nodes, or to mastoid and spinal accessory nodes.
Haematogenous spread
Nasopharyngeal carcinoma may spread early in its course to bone, liver and lung. This often occurs early in the course of the disease.
Neurological spread
The nasopharynx is innervated by numerous branches of the glossopharyngeal and vagus nerves. These form a plexus around the pharynx with added contribution from sympathetic nerves arising in the superior cervical ganglion. Involvement of the glossopharyngeal or vagus nerves may enable the tumour to spread more easily through the jugular foramen.
Nasopharyngeal carcinoma seems to spread rapidly along the maxillary and mandibular divisions of the trigeminal nerve, leading to intracranial deposits of disease.
