The pyriform sinus, also known as the piriform fossa or piriform recess, is a pair of pear-shaped anatomical indentations located in the lower part of the throat, called the hypopharynx. These recesses sit on either side of the laryngeal inlet, the opening to the voice box. This structure functions as a channel that ensures liquids and food safely bypass the airway.
Anatomy and Location in the Throat
The pyriform sinus is a distinct depression situated posterolaterally within the pharynx, the muscular tube behind the nose and mouth. To visualize its position, one can imagine a small gutter on either side of the entrance to the larynx.
Medially, the boundary is formed by the aryepiglottic fold, a triangular membrane connecting the side of the epiglottis to the arytenoid cartilage. Laterally, the recess is bordered by the thyroid cartilage, often referred to as the Adam’s apple, and the associated thyrohyoid membrane.
Primary Role in Swallowing
The primary physiological function of the pyriform sinus is to facilitate the efficient passage of a bolus during swallowing, known as deglutition. It acts as a diversionary conduit, directing liquids and food away from the opening of the trachea, or windpipe. This rapid channelling is necessary to prevent aspiration, the accidental entry of material into the lungs.
During the pharyngeal phase of swallowing, the epiglottis covers the laryngeal inlet to protect the airway. The pyriform sinuses then form the final path, guiding the material around the closed larynx and into the upper esophageal sphincter. This bypass mechanism ensures that the food bolus is propelled directly into the esophagus. When swallowing function is impaired, material can pool in this space, increasing the risk of aspiration after the swallow has completed.
Clinical Importance: Head and Neck Cancer
The pyriform sinus is a common site for the development of malignant disease, specifically Squamous Cell Carcinoma. This region is the most common location for cancers originating in the hypopharynx, accounting for approximately 65% to 85% of cases. The deep location of the sinus means that tumors often grow substantially before causing noticeable symptoms, leading to a late stage of diagnosis for many patients.
The area has a rich network of lymphatic vessels, resulting in a high rate of regional lymph node metastasis, occurring in up to 70% of lesions upon initial presentation. Common symptoms include persistent throat pain, difficulty swallowing (dysphagia), and sometimes a sensation of having a lump in the throat. Due to the advanced stage at diagnosis, most tumors are classified as T3 or T4, often requiring complex treatment plans.
Addressing Other Common Clinical Issues
Beyond malignancy, the pyriform sinus is a frequent site for foreign body impaction. Small, sharp items such as fish bones or chicken splinters often become lodged in the recess because of its depression-like structure. This impaction can cause acute, localized pain and the sensation that a foreign object is stuck in the throat.
Another clinical issue associated with the surrounding area is the formation of Zenker’s diverticulum, a pouch that develops just below the pyriform sinus at the pharyngo-esophageal junction. While not directly in the sinus, this condition involves a structural weakness that causes a mucosal sac to bulge outward. This pouch can trap food and liquid, which can lead to regurgitation and chronic swallowing difficulties.