Tonsillar fossa

The tonsillar fossa (a.k.a. tonsillar sinus) is a recess in the lateral wall of the oropharynx that forms the anatomical bed of the palatine tonsil. It is bounded anteriorly by the palatoglossal arch and posteriorly by the palatopharyngeal arch, with the palatine tonsil occupying most of the interval between these two mucosal folds.

Supratonsillar fossa

Although the palatine tonsil occupies the majority of the tonsillar fossa, it does not completely fill the space. At the superior aspect of the fossa, above the upper pole of the tonsil, a small recess persists between the palatoglossal and palatopharyngeal arches, known as the supratonsillar fossa. This recess forms an important anatomical subdivision of the tonsillar fossa and may serve as a site for retention of desquamated epithelium, secretions, and infective material.

Plica semilunaris (semilunar fold)

The superior part of the tonsillar fossa also contains a delicate crescent-shaped mucosal fold termed the plica semilunaris. This fold extends between the palatoglossal and palatopharyngeal arches and partially overlies the supratonsillar fossa. Its prominence is variable, but when well developed it contributes to the configuration of the superior tonsillar recess.

Plica triangularis

Another mucosal fold associated with the tonsillar fossa is the plica triangularis (triangular fold), which extends from the posterior surface of the palatoglossal arch across the anteroinferior aspect of the palatine tonsil. By partially covering the medial surface of the tonsil, this fold may create a recess between itself and the tonsillar tissue, contributing to the formation of the tonsillar sinus. In some individuals, adhesions may obliterate this space.

Clinical correlates

These mucosal folds and recesses are clinically significant because the crypts and spaces within the tonsillar fossa can trap epithelial debris, food particles, and bacteria, predisposing to recurrent infection and chronic tonsillitis.

Medial and lateral surfaces of palatine tonsil

• The medial surface of the palatine tonsil projects into the cavity of the oropharynx from the tonsillar fossa and contains multiple openings of tonsillar crypts, which increase the surface area available for immunological surveillance.

• The lateral surface is covered by a fibrous capsule that forms the boundary between the tonsil and the wall of the tonsillar fossa.

• Lateral to this capsule lies loose connective tissue separating the tonsil from the superior constrictor muscle, collectively forming the tonsillar bed.

Clinical correlates (neurovascular relations of tonsillar fossa)

The tonsillar fossa is also of surgical importance because of its close neurovascular relations. The tonsillar branch and ascending palatine branch of the facial artery lie in close proximity to the tonsillar bed and are important sources of haemorrhage during tonsillectomy. Posterolaterally, the internal carotid artery lies approximately 2-2.5 cm from the fossa. The glossopharyngeal nerve is closely related to the lateral wall of the tonsillar fossa and may account for referred otalgia experienced during tonsillitis.