The pyriform sinus is a pear-shaped passage that flanks the sides of the larynx, or voice box. It is a component of the structure in the body responsible for speech. Alternative terms include piriform sinus, piriform recess and piriform fossa.
At its upper region, the pyriform sinus is bound between a fold of mucous membrane called the aryepiglottic fold. Also known as the aryepiglottis, it constitutes the borders of the larynx's opening. This sinus is flanked by the thyroid cartilage, which is the laryngeal skeleton's biggest flexible connective tissue; and the hyothyroid membrane, which surrounds this cartilage. At the bottom of the pear-shaped recess is the cricoid cartilage, a ring-shaped tissue that surrounds the tube connecting the larynx to the lungs.
The mucous membrane that surrounds the pyriform sinus has two branches of the cranial vagus nerve: the recurrent laryngeal nerve and the internal laryngeal nerve. The former is dubbed "recurrent" because of its irregular path, such as rising up in the region between the windpipe called the trachea and the food pipe named the esophagus, while diving into the region between the head and abdomen referred to as the thorax. The internal laryngeal nerve is the internal branch of the superior laryngeal nerve. Both organ systems are responsible for supplying sensation to the larynx.
Any tampering, defect or destruction of either of these nerves by the pyriform sinus could cause adverse effects to the larynx. One could cough uncontrollably if the internal laryngeal nerve is irritated by food particles or water trapped in this sinus. This condition is most common with infants, and in some cases, it might develop into a bacterial infection called acute infectious thyroiditis. Also, a paralysis of the organ it springs from, the superior laryngeal nerve, alters voice pitch into a hoarseness and could become permanent if it remains for a couple of months.
Pyriform sinus is associated with neck and head cancer. It is located in the hypopharynx, or the lower part of the throat region that joins to the esophagus called the pharynx. In about 70 percent of all hypopharyngeal cancer cases, the tumors are specifically located in the pyriform sinus. Since it is hard to diagnose, hypopharyngeal cancer is usually discovered at stage III, which indicates a significant progression of the disease and reduces the chance of survival.