Pharyngeal Constrictors

Three overlapping muscles — superior, middle and inferior — that form the back and side walls of the pharynx and squeeze food down during swallowing.

Three overlapping muscles that squeeze food and liquid down from the mouth into the esophagus when you swallow.

Dose to the constrictors is linked to long-term dysphagia, one of the most important late effects after head and neck radiotherapy. Many constrictor segments lie next to or inside the target in oropharynx and hypopharynx cancer, so sparing is often partial: the goal is to reduce the dose to the parts outside the target. Some protocols contour the three muscles separately; others (like RTOG 0920's "OAR pharynx") use one structure of uninvolved pharyngeal wall and adjacent constrictors.

Brouwer 2015 contours the constrictors as one structure, about 3 mm thick:

• Top: the lower tips of the pterygoid plates.
• Bottom: see the note below.
• Front: at the top, the hamulus of the pterygoid plate, the mandible, the base of tongue and the pharyngeal lumen; in the middle, the base of tongue and the hyoid; at the bottom, the soft tissue of the supraglottic and glottic larynx.
• Back: the prevertebral muscle.
• Sides: at the top, the medial pterygoid muscle; in the middle, the greater horn of the hyoid; at the bottom, the superior horn of the thyroid cartilage.

Note on the lower limit: Brouwer's text places it at the lower edge of the cricoid cartilage, while its Table 1 lists the lower edge of the arytenoid cartilages (where its separate cricopharyngeal inlet structure begins). Published guidelines vary most at the top and bottom of this structure, so check which definition your protocol uses. Brouwer notes the constrictors can be subdivided for research — Christianen 2011 is one such reference.