The urachus is a tube-like structure that forms in a developing embryo. It connects the umbilical cord to the urinary bladder before birth. After birth, the urachus usually shrinks into a small ligament. However, traces of the urachus (called urachal residues) can be detected in up to one-third of adults. Urachal residues usually do not cause any symptoms.
A growth of cancerous cells that starts in the urachus is called urachal cancer.
Because of its location, urachal cancer can grow into the abdominal wall and the abdominal cavity. Often it infiltrates the roof of the urinary bladder. Urachal cancer can grow for a long time before causing symptoms. As a result, it is often detected at later stages.