The urachus is a small tube-like structure that runs along the midline of your abdomen, connecting the top of the bladder to the belly button. In a developing fetus, it serves as part of the urinary drainage system. By around the 12th week of pregnancy, this channel normally seals itself off and becomes nothing more than a thin fibrous cord called the median umbilical ligament. Most people go their entire lives without knowing it exists, but when it doesn’t close properly, it can cause problems ranging from minor drainage at the belly button to, in rare cases, cancer.
How the Urachus Forms Before Birth
During early fetal development, a structure called the allantois helps manage waste. The urachus forms from the far end of the allantois, creating a channel between what will become the urinary bladder and the umbilical cord. This channel allows urine to drain out of the fetus and into the surrounding amniotic fluid.
As the fetus grows, the bladder descends into the pelvis and the urachus gradually narrows. By roughly 12 weeks of gestation, the channel closes entirely. What remains is a small, solid band of fibrous tissue, the median umbilical ligament, embedded in the tissue behind the abdominal wall between the bladder and the navel. It has no function after birth.
What Happens When the Urachus Doesn’t Close
Sometimes the urachus fails to seal off completely, leaving behind a remnant that can take several forms depending on which portion stays open.
- Patent urachus: The entire channel remains open from the bladder to the belly button. This is the most obvious type, because urine leaks from the navel. In newborns, the telltale sign is a near-constant wet discharge from the umbilicus, often with skin irritation around it. If there’s any doubt about whether the fluid is urine, testing it for creatinine (a waste product found in urine) confirms the diagnosis. Babies with a patent urachus are also prone to recurrent urinary tract infections.
- Urachal cyst: The middle section of the urachus stays open as an isolated pocket of fluid, with both ends sealed. Because it’s buried in the abdominal wall, it often produces no symptoms until it becomes infected.
- Urachal sinus: One end of the urachus (the belly button end) stays open while the rest closes. This can cause persistent or intermittent drainage from the navel.
- Vesicourachal diverticulum: The bladder end stays open, forming a small pouch that bulges off the top of the bladder. This type is frequently discovered by accident on imaging done for unrelated reasons.
Symptoms of an Infected Urachal Cyst
Urachal cysts can sit quietly for years, even decades, before announcing themselves. The trigger is almost always infection. When a cyst becomes infected, it can produce fever, lower abdominal pain, tenderness and redness over the lower belly, nausea, vomiting, and painful urination. Some people develop a palpable mass below the navel. The bacteria involved are typically the same species that cause urinary tract and skin infections.
Infected cysts in adults are sometimes mistaken for other conditions, including appendicitis or an abdominal abscess, because the symptoms overlap. The location of the pain, right along the midline between the bladder and navel, is the main clue that points toward a urachal problem.
How Urachal Remnants Are Diagnosed
Ultrasound and CT scans are the primary tools. On ultrasound, a patent urachus shows up as a tube-like structure running from the top of the bladder toward the belly button, just beneath the abdominal wall. Urachal cysts appear as fluid-filled pockets in the midline of the lower abdomen. A vesicourachal diverticulum looks like a small fluid-filled sac protruding from the top of the bladder.
One diagnostic challenge is distinguishing an infected cyst from something more serious like urachal cancer, because both can appear as thick-walled, mixed-density masses on imaging. When the imaging is ambiguous, a needle biopsy or fluid sample is typically needed to clarify the diagnosis.
Treatment for Symptomatic Remnants
If a urachal remnant causes symptoms or becomes infected, complete surgical removal is the standard approach. Simply draining an infected cyst and treating with antibiotics isn’t enough on its own: roughly 30% of cases managed that way develop repeat infections. Complete excision also eliminates the small but real risk of cancer developing in the remnant tissue later in life.
Surgery can be done through a traditional open incision or laparoscopically (through small incisions using a camera). The laparoscopic approach results in less pain, better cosmetic outcomes, and faster recovery. In one comparison, patients who had laparoscopic surgery returned to normal activities in about 11 days on average, compared to nearly 16 days for those who had open surgery. Hospital stays were also significantly shorter with the laparoscopic approach, averaging under 2 days when the bladder itself didn’t need repair, versus close to 4 days with an open procedure.
Urachal Cancer
Cancer arising from the urachus is extremely rare, with an estimated incidence of about 1 in 5 million people per year, accounting for less than 1% of all bladder tumors. The overwhelming majority of these cancers are adenocarcinomas, a type of cancer that forms in mucus-producing gland cells. This is notable because most bladder cancers are a different type entirely, which is one of the ways doctors distinguish urachal cancer from ordinary bladder cancer.
These tumors typically develop in the dome or front wall of the bladder, where the urachus originally attached. Diagnosis involves specific criteria established by the World Health Organization: the tumor must be centered in the bladder wall at the dome, and there should be no evidence of the more common type of bladder cancer elsewhere in the organ.
The prognosis depends heavily on whether the cancer can be surgically removed. For patients with resectable tumors, the five-year survival rate sits around 50%. For those with cancer that has already spread, outcomes are considerably worse. Geographic patterns exist as well. Incidence is highest in Japan and lowest in Canada, though the reasons for this variation aren’t fully understood.