Urachus

What is a urachus?

The urachus (yer-UH-kus) is a fibrous tube (canal) that extends between the urinary bladder to the navel (belly button) in a fetus. It’s how pee (urine) leaves the fetus during the first trimester.

In most fetuses, the urachus closes before birth — usually during the last week or so of the first trimester.

Is the urachus the belly button?

No, the urachus isn’t the belly button. It’s a tube where pee initially drains during the first trimester.

Your belly button is the spot where the umbilical cord attaches to your abdomen as a fetus. A healthcare provider cuts it shortly after birth. The umbilical cord carries oxygen and nutrient-rich blood to a fetus. It also carries away pee that it receives from the urachus.

What is the function of the urachus?

During the first trimester, the urachus helps remove a fetus’s pee through the birthing parent’s placenta by way of the umbilical cord. As the fetus develops, its bladder begins to move toward its pelvis. As this happens, the urachus stretches and develops into a small, fibrous cord (median umbilical ligament).

Do adults have a urachus?

In most adults, the urachus develops into the median umbilical ligament. But about 33% of adults still have some urachal tissue. Many adults with urachal tissue don’t even realize it because it usually doesn’t cause any problems.

Do females have a urachus?

All fetuses have a urachus, regardless of their sex. Most of the time, the urachus develops into a ligament at the end of the first trimester.

Where is the urachus located?

The urachus extends between the top-front part (dome) of a fetus’s bladder and belly button.

What does the urachus look like?

The urachus looks like a thick tube or cord. It may pinch in (taper) at both ends, or one end may be wider than the other, like a funnel. The length of a urachus can vary between 1 centimeter and 15 centimeters (about 0.4 inches to 6 inches) — a little shorter than an aspirin tablet or about as long as a pen.

What are the most common tests to check the urachus?

If a healthcare provider thinks your baby might have a urachal problem, they’ll recommend an ultrasound. An ultrasound is a painless, noninvasive imaging test that allows providers to see your baby’s internal tissues and organs. They may also recommend an MRI. An MRI is another type of painless imaging test.

If a provider suspects that your baby has a patent urachus and that wetness around their belly button is coming from their bladder, they’ll test the fluid to see if it contains urea or creatinine. Urea and creatinine are waste products that typically leave their body through their pee.

Another test that can provide a clear view of the tissue behind your baby’s belly button is a voiding cystourethrogram (VCUG). During a VCUG, a provider injects a dye through their urinary system into their bladder. A VCUG is useful if your baby also has a problem with their bladder’s structure.

What is the remnant of the urachus?

A urachal remnant is when the urachus doesn’t close. There are different types of urachal remnants, which include:

• Patent urachus. This occurs when the urachus doesn’t close as expected. It’s completely open, which may cause pee to leak out of your baby’s belly button or a wet, irritated and discolored (red, brown or purple) area around their belly button (granuloma).
• Urachal cyst. A urachal cyst is when the urachus doesn’t close and a pocket of tissue and pus (cyst) forms between your baby’s belly button and bladder. A urachal cyst usually doesn’t have any symptoms. But a bacterial infection can occur and cause symptoms, including abdominal pain and bloody or cloudy fluid near the belly button.
• Urachal sinus. This occurs when the urachus doesn’t close as expected near your baby’s belly button but closes at their bladder. A urachal sinus usually doesn’t have any symptoms. But a bacterial infection may cause abdominal pain and bloody or cloudy fluid near their belly button.
• Diverticulum. A diverticulum is when the urachus doesn’t close as expected near your baby’s bladder. It usually doesn’t cause any symptoms. But sometimes, pee can get trapped in this area, which may cause urinary tract infections (UTIs). UTI symptoms may include fever and pain or burning when your baby pees (dysuria).

Another name for a urachal remnant is a urachal abnormality.

What is urachal cancer?

Urachal cancer is a rare type of bladder cancer. It most often appears in people who are 50 or older who have urachal tissue. Urachal cancer symptoms may include:

• Blood in your pee (hematuria)
• Mucus in your pee (mucinuria)
• Bacteria in your pee (bacteriuria)
• Abdominal pain
• A lump in your abdomen (abdominal mass)

What are common treatments for the urachus?

A healthcare provider may recommend chemical cauterization if your baby has persistent wetness around their belly button area. During chemical cauterization, a provider applies a small amount of a chemical (like silver nitrate, ferric subsulfate solution or aluminum chloride hexahydrate). The chemical usually helps the area heal within a few days. They may need to take antibiotics afterward.

Antibiotics are also very effective at treating urachal cysts. In some cases, a provider may need to drain fluid from the cyst with a needle. After the cyst heals, your baby may need surgery to remove the urachus and anything that connects to it, like the top of their bladder. Leaving urachal tissue behind increases your baby’s risk of developing urachal cancer or other conditions, including infections or bladder stones. But most people who have a provider remove their urachal tissue don’t have any further problems.