Is a potential space that lie on either side of the larynx. They are two in number. It is shaped like a pyramid with the base poinint above and the apex below. They belong to the hypopharyngeal area of the pharynx. It has two parts; the shallow upper part and a deeper lower part.
The pyriform fossa is bounded laterally by the mucosa covering the lamina of the thyroid cartilage. Medially it is bounded by the aryepiglottic fold and arytenoid cartilages above and the cricoid cartilage below. Superiorly it is bounded by the lateral glosso epilglottic fold (Pharyngoepiglottic fold), inferiorly it continues with the oesophagus.
Diagram showing Pyriform fossa
Deep to the mucous membrane of the lateral wall of the pyriform fossa lies the internal laryngeal branch of the superior laryngeal nerve. It supplies sensori fibres to this area.
Clinical importance of pyriform fossa:
1. Anatomically it is a hidden area. Any malignancy in this area will initially cause fewer symptoms and has a tendency to present very late.
2. This area is richly endowed with lymphatics. They drain into the upper deep cervical group of lymph nodes. Any malignancy in this area has a tendency for nodal metastasis.
3. Foreign bodies in the throat commonly gets lodged here.
4. Since superior laryngeal nerve lies superfically in this area, it can be topically blocked by placing cotton plegets soaked in 4% xylocaine in this area. This is known as the pyriform fossa block.
Examination of the pyriform fossa:
The superficial shallow portion of the pyriform fossa is easily visible in a laryngeal mirror. This portion will be visible in the indirect laryngoscopy examination. The deeper portion of the pyriform fossa is hidden and is not visible to the IDL mirror. Only a direct examination using a upper oesophageal speculum will reveal this portion.
Tumors involving the pyriform fossa commonly arise from its deep portion. This may escape detection during a IDL scopy examination. But if one looks for pooling of saliva in the involved pyriform fossa the underlying growth can be suspected. Hence pooling of saliva is an important clinical sign indicating a under lying tumor in the deep portion of the pyriform fossa, or the presence of a foreign body can also be suspected by this sign.
Causes for pooling of saliva in the pyriform fossa:
Pooling of saliva in the pyriform fossa is not only caused by growth affecting this area causing obstruction to saliva being swallowed, but also due to intense cricopharyngeal muscle spasm.
1. Malignant growth involving the deep portion of the pyriform fossa
2. Foreign body being lodged in the pyriform fossa.
3. Growth involving the crico pharynx or upper oesophagus can also cause pooling of saliva.