Urachal Cyst

A urachal cyst is a fluid filled, epithelium lined cavity within a persistent segment of the urachal remnant, closed at both the bladder and umbilical ends. It is the commonest symptomatic urachal remnant in older children and adults, with the cyst typically measuring 2 to 10 cm.

The cyst sits in the midline of the lower abdominal wall between the umbilicus and the bladder dome, deep to the rectus sheath and anterior to the peritoneum. It arises when a central part of the urachus fails to regress while the ends obliterate.

The lining is transitional or columnar epithelium, and desquamated cells accumulate. The contents become infected in about one third. Organisms include Staphylococcus aureus, Escherichia coli, Proteus, Enterococcus, and polymicrobial flora.

An infected cyst can rupture into the peritoneum (peritonitis), the bladder, the umbilicus or the abdominal wall.

Rarely, a calcified or thick walled cyst contains adenocarcinoma or squamous cell carcinoma. Adults over 40 are at greater risk.

• Asymptomatic, found incidentally at imaging, in many.
• Infected cyst: lower abdominal pain (midline, infraumbilical), fever, nausea, dysuria and urinary frequency (from bladder irritation), and a tender, firm midline infraumbilical swelling; erythema of the abdominal skin.
• Peritonitis if the cyst ruptures into the peritoneal cavity; discharge of pus from the umbilicus if it drains through a sinus; pyuria if it drains into the bladder.
• Palpable mass in the lower midline, with signs of local inflammation.
• Malignant change: haematuria, a mass that is fixed, pain, mucus in urine, weight loss.
• Often mistaken for appendicitis, diverticulitis, omphalitis, or ovarian cyst.

• Ultrasound: a midline anechoic or hypoechoic fluid filled structure in the abdominal wall anterior to the peritoneum between the umbilicus and bladder dome; infected cysts show thick walls with debris and air.
• CT with contrast: a well defined midline cystic mass along the course of the urachus, with rim enhancement when infected, and calcification in malignant lesions.
• MRI for detail of the extent and relationships; cystoscopy to exclude bladder connection or tumour.
• Laboratory: raised white cell count, C-reactive protein, urine microscopy and culture, blood cultures when septic.
• Needle aspiration is avoided because of seeding and secondary infection; send fluid for culture only when draining an abscess.
• Biopsy or frozen section in adults with a suspicious solid component.

• Asymptomatic small cysts in children: observation with periodic ultrasound; many resolve. In adults, because of malignant potential, elective excision is advised for persistent cysts.
• Infected cyst or abscess: admission and intravenous antibiotics covering skin and urinary flora for 5 to 7 days.
• Intravenous options are ampicillin sulbactam 50 mg/kg of ampicillin component every 6 hours in children, or 3 g every 6 hours in adults. Alternatively give ceftriaxone 1 to 2 g daily with metronidazole 500 mg every 8 hours.
• Then give oral antibiotics (amoxicillin clavulanate) to complete 10 to 14 days.
• For an abscess, use percutaneous ultrasound guided drainage or open incision and drainage. Leave a drain in place until the output stops.
• Definitive treatment is complete surgical excision of the cyst with the entire urachal remnant and a cuff of bladder dome (when attached). Operate at an interval of 4 to 8 weeks after infection has resolved, through an infraumbilical midline incision or laparoscopically.
• Preserve the peritoneum where possible. Retain or excise the umbilicus depending on the extent of the tract. Incomplete excision leads to recurrence.
• Urethral catheter for 3 to 5 days if the bladder was opened, and cystogram if leak suspected.
• Malignancy: partial or radical cystectomy with en bloc urachal ligament, umbilicus, and pelvic lymph node dissection; adjuvant chemotherapy (5-fluorouracil, cisplatin) in advanced stages.
• Complications: surgical site infection, bladder leak, recurrence, and hernia.
• Prognosis is excellent for benign disease with complete excision.