Controversy still exists over the exact contributions of the allantois and the ventral cloaca to urachal formation.
Four anatomic urachal variants have been described, depending on the degree of urachal tubularization and the status of associated umbilical vessels.
1. Patent Urachus
Failure of complete urachal lumen closure results in free communication between the bladder and the urachus, and urine leaks from the umbilicus. Lower urinary tract obstruction may also be a contributing factor.
The diagnosis can be made at birth or soon thereafter, when the umbilical cord is ligated and urine drains from the umbilicus. A tumor-like protrusion from the umbilicus is frequently seen, and occasionally an umbilical hernia may also be present.
A confirmation of the diagnosis can be obtained by analyzing the fluid for urea and creatinine or injecting methylene blue via a catheter into the bladder. Conversely, indigo carmine can be injected into the fistulous tract to look for a color change in the urine. A voiding cystourethrogram is important to rule out any lower tract obstruction, and it may also demonstrate the communication.
Early treatment is recommended because umbilical excoriation, recurrent urinary infection, septicemia and stone formation may develop.
Neither cauterization of the umbilical lumen alone nor simple ligation has yielded satisfactory results. Complete excision of the urachus and umbilicus with a cuff of bladder by an extraperitoneal approach is a standard method of treatment. In addition, if there is any lower urinary tract obstruction, this also requires treatment.
2. Urachal Cyst
When the urachal lumen incompletely obliterates, there exists the potential for cystic development within this epithelial lined space. Most cysts develop in the lower third of the urachus.
The cyst generally remains small and silent. Occasionally, it is felt as a midline lower abdominal mass. More often, symptoms are related to size or secondary infection.
Septic cysts most commonly present in adults, but some have been reported in infants. These cysts then produce localized pain and sometimes inflammation in association with systemic symptoms. If left untreated, the abscess will often drain from the umbilicus or into the bladder.
The differential diagnosis of a palpable uninfected cyst includes a bladder diverticulum, umbilical hernia and ovarian cyst. An infected cyst may be difficult to differentiate from acute appendicitis.
Lower abdominal ultrasound and especially CT scans are excellent methods of confirming the diagnosis.
An infected cyst is best treated by incision and drainage with subsequent excision.
3. Urachal Sinus
A urachal sinus is probably the sequela of a small urachal cyst that became infected and dissected to the umbilicus. Rarely, it may drain into the bladder; the cyst position probably dictates the primary direction of drainage. The symptoms and treatment are similar to the other urachal anomalies already described.
The diagnosis of a draining urachal sinus may be difficult to differentiate from an umbilical granuloma or umbilical sinus. A fistulogram may be helpful.
4. Vesicourachal Diverticulum
Complete obliteration of the urachus at the umbilicus and incomplete closure at the bladder level may result in a vesicourachal diverticulum. Lower urinary tract obstruction may or may not be a related factor. This problem is usually discovered during radiologic evaluation for a urinary tract infection via a VCUG. Occasionally, stones have been detected within the diverticulum.
RELATED UMBILICAL DISORDERS
These result from incomplete closure of the omphalomesenteric duct.
1. Omphalomesenteric duct.
This is extremely rare and may be recognized with fecal drainage noted from the umbilicus. It is more common in boys than in girls, and differentiation from urachal anomalies is important for the surgical approach. Confirmation is done through a fistulogram.
2. Partially patent omphalomesenteric duct.
A. Omphalomesenteric duct sinus.
B. Omphalomesenteric duct cyst.
This can be diagnosed with fistulograms and require excision.
3. Meckel’s diverticulum.
Persistence of the proximal portion of the omphalomesenteric duct as a diverticulum opening into the ileum is called a Meckel’s diverticulum. It may be associated with an umbilical polyp.
4. Umbilical polyp.
Persistence of intestinal mucosa at the umbilicus can develop into an umbilical polyp. Probing and possibly a fistulogram are important. A simple polyp can be treated superficially with silver nitrate or local excision. It is important, however, to make sure that it is not associated with a duct remnant.
Failure of the intestines to recede into the abdominal cavity by the end of the tenth week of gestation results in an omphalocele.
About 50% of infants with an omphalocele have other congenital anomalies.
6. Umbilical hernia.
This is usually congenital and relates to the incomplete closure of the anterior abdominal wall fascia after the intestines have returned to the abdominal cavity.
Inflammation of the umbilicus
B. Single umbilical artery
Controversy still exists over the single umbilical artery as a barometer of other congenital anomalies. Certainly, the incidence of urinary tract abnormalities is not significantly increased in newborns with a single umbilical artery.