The canal of Nuck is a small area of peritoneum just anterior to the round ligament that everts and protrudes through the inguinal ring and toward the labia majora. Usually the canal itself disappears before birth or during the first year of life. If it remains patent, patients may develop an inguinal hernia or a communicating hydrocele.

A canal of Nuck cyst is defined as a hydrocele (fluid-filled hernia of the peritoneum) that extends into the inguinal canal. It is a very rare condition, and the specific etiology of formation of the cyst is unknown. These cysts often present as painless swelling in the labial or inguinal regions. Patients may describe that a bulge appears with standing and improves when supine. Some patients will have symptoms of pain (especially after periods of standing) associated with the swelling.