Anatomy

The pharynx, an incomplete muscular tubular structure, is divided into nasopharynx, oropharynx, and hypopharynx depending on its relationship with the oral cavity. Anatomically, the nasopharynx is above the oral cavity, the oropharynx is at the same level as the oral cavity, and the hypopharynx is below the oral cavity.

The nasopharynx is located behind the nasal cavity and it continues inferiorly into the oropharynx. It is a potential space enclosed by roof, floor, and posterior and lateral walls. The superior constrictor forms the muscular wall of the nasopharynx on the posterior and lateral walls only. The average anteroposterior distance ranges from 2 to 3 cm while both the transverse and vertical diameters range from 3 to 4 cm. There are considerable variations between individuals and, even in one person, its volume and shape change with the position of the patient and during various movements of the organs of the oral cavity.1

Anteriorly, the two choanae of the nasal cavity continue into the nasopharynx, where the posterior edge of the nasal septum that separates the choanae constitutes part of the anterior wall. The roof is formed by the continuation of the rostrum posterior to the undersurface of the body of the sphenoid, which slopes backward and downward to merge with the posterior wall. The posterior wall is formed by the anterior surface of the arch of the atlas and the upper portion of the body of the axis. The floor opens into the oropharynx and, when the soft palate moves upward to close this potential space, the pharyngeal isthmus, the upper surface of the soft palate becomes the floor of the nasopharynx (Fig. 22.1).

High on the lateral wall of the nasopharynx is the orifice of the eustachian tube, followed inferiorly by the superior constrictor muscle. The pharyngeal openings of the eustachian tube are enclosed by an incomplete cartilaginous ring, which is deficient inferolaterally. This cartilaginous ring on the medial side of the opening forms an elevation of mucosa; this is the torus tubarius. Medial to this elevation is the pharyngeal recess or fossa of Rosenmüller, which is a slitlike space of variable depth, shape, and size (Fig. 22.2). The opening of the recess may be narrow or wide and the recess may extend laterally, occasionally to above the superior constrictor muscle. The fossa of Rosenmüller is the most common site where NPC is found. Tumor in the fossa may infiltrate nearby structures before growing into the lumen of the nasopharynx. Due to the close proximity of the fossa to structures at the skull base, these structures may be affected early in the course of the disease and contribute to the presenting clinical features.

The epithelial lining of the nasopharynx mainly consists of pseudostratified ciliated columnar cells; this starts at the choana area and extends to the roof and lateral wall. In the posterior wall most of the lining epithelium is composed of stratified squamous cells. These epithelial cells lie on a distinct basement membrane and the lamina propria contains abundant lymphoid tissue (Fig. 22.3). The enclosing muscular layer comprises the superior constrictor muscle that is deficient in the upper part of the lateral wall where the eustachian tube passes medially, separating it from the upper edge of the muscle and the skull base. External to and enclosing the muscle is the pharyngobasilar fascia, which covers the posterior and lateral aspects of the superior constrictor. This fascia is attached to the basiocciput superiorly and forms a median raphe in the posterior midline. This pharyngobasilar fascia is a solid sheet of fibrous tissue that extends laterally to the medial pterygoid plate while inferiorly it merges with the buccopharyngeal fascia. Posteriorly, behind the superior constrictor are the prevertebral muscles with the prevertebral fascia and then the vertebrae.

The fascia around the nasopharynx form a few potential spaces and each of them contains important structures. These spaces to some extent influence the pathway of tumor spread.

1. 
   

   The retropharyngeal space lies between the pharyngobasilar fascia and the prevertebral fascia, and is a part of the retrostyloid portion of the paranasopharyngeal space. It is found on both sides, paramedian in location, situated lateral to the median raphe of the pharyngobasilar fascia. The retropharyngeal space contains the lymph node of Rouvière, the first lymph node station that may be affected when a tumor extends through the lymphatic channel (Fig. 22.4).

   
   
2. 
   

   The parapharyngeal space is lateral to the pharynx and is divided by the styloid process and its attachments into the prestyloid and retrostyloid compartments. The former is located lateral to the fossa of Rosenmüller and contains the maxillary artery and nerves. The more posteromedially retrostyloid located compartment contains the contents of the carotid sheath, the last four cranial nerves, the sympathetic trunk, and the upper deep cervical lymph nodes (Fig. 22.5). The tumor in the nasopharynx involves the prestyloid compartment by direct extension, and once there it may infiltrate the maxillary nerve and, extending upward, the trigeminal nerve. The retrostyloid compartment can be affected either by direct tumor extension and invasion or by lymphatic spread. The associated symptoms reflect the involvement of the respective cranial nerves.

The arterial supplies of the nasopharynx are abundant; these are the ascending pharyngeal, ascending palatine, and pharyngeal branches of the sphenopalatine artery, all of which originate from the external carotid artery. The venous plexus beneath the mucosal membrane communicates with the nearby pterygoid plexus. There is a well-developed submucosal plexus of lymph vessels in the nasopharynx that drains primarily into the retropharyngeal lymph nodes and sometimes directly to the cervical nodes. Efferents from the retropharyngeal group of nodes drain to the deep cervical lymph nodes. As the nasopharynx is a midline structure, the efferents of lymphatics draining the central area frequently reach lymph nodes on both sides of the neck.

Pathologies

Adenoids

The lymphoid tissue and nodules are present submucosally extending from the nasopharynx laterally to the eustachian tube orifices and then inferiorly to the soft palate and along the lateral wall to the tonsils. Medially the lymphoid tissue extends to the tongue base. This forms the Waldeyer′s ring of lymphoid tissue and is regarded as the first line of defense.

Adenoids are aggregates of lymphoid follicles and nodules in the nasopharynx that have increased in size physiologically or have formed a mass in response to repeated inflammation, and that may produce symptoms. This usually happens in children between 3 and 7 years of age. The symptoms related to the increase in size are nasal obstruction or decreased hearing due to serous otitis media when the eustachian tube openings are blocked. This might also account for obstructive sleep apnea in children.3 When there is associated infection, additional symptoms may include nasal discharge, postnasal drip, otitis media, and generalized malaise. The diagnosis is usually made by the clinical features and endoscopic examination of the nasopharynx. The adenoids usually regress after adolescence, although in some patients the lymphoid tissue may persist as a mass in the nasopharynx even when they are adults. Biopsy under endoscopic view is indicated to differentiate it from other pathologies in the nasopharynx (Fig. 22.7).

The treatment should start with medication such as topical corticosteroids if there is an allergic element or mild decongestant nasal drops; if symptoms escalate despite medication, then adenoidectomy is indicated.

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