Urachal remnant

A urachal remnant is a persistent segment of the urachus, a midline embryologic structure that normally obliterates before birth. Its persistence results in various urachal anomalies, including urachal sinus, urachal cyst, vesico-urachal diverticulum, and patent urachus.

The urachus is derived from the allantois, a projection from the yolk sac that appears around day 16 of gestation and connects the fetal bladder to the umbilicus. As the bladder descends during fetal development, the urachus normally narrows and obliterates by birth to form the median umbilical ligament. Failure of this process results in persistent urachal tissue, giving rise to anomalies such as urachal sinus, cyst, diverticulum, or a patent urachus. The urachus typically measures 3-10 cm in length and 8-10 mm in diameter and is composed of three layers: a transitional epithelial lining, a connective tissue core, and an outer muscular layer continuous with the detrusor muscle. Resected specimens from symptomatic and asymptomatic patients may contain epithelial components, and some may show signs of inflammation or cystic degeneration, highlighting the potential for clinical complications even in previously unremarkable remnants.

The reported prevalence of urachal remnants varies widely depending on diagnostic criteria and study methodology. In surgical series, such as patients undergoing laparoscopy for inguinal hernia repair, visible residual urachal tissue has been observed in up to 35.4% of cases, particularly in infants under 1 year of age, suggesting physiologic regression with age. In contrast, ultrasonographic studies in patients under 18 years report a much lower prevalence of around 0.2%. Urachal remnants are slightly more common in males. Reported subtype distributions include patent urachus (10-48%), urachal cyst (31-43%), urachal sinus (18-43%), and urachal diverticulum (3-4%).

Urachal remnants are congenital anomalies more frequently diagnosed in males.

Urachal remnants are most often asymptomatic and discovered incidentally. When symptomatic, presentations vary by age and remnant type. In infants, the most common signs include umbilical granulation tissue, discharge, and erythema. A patent urachus may cause continuous or intermittent urine leakage from the umbilicus, leading to persistent irritation. In older children, abdominal pain is a more frequent symptom. Urachal cysts may present either incidentally or when infected, leading to umbilical discharge of pus, suprapubic pain, or recurrent UTIs if the cyst communicates with the bladder. Infected urachal anomalies can present with high fever, abdominal tenderness, LUTS, or a palpable abdominal mass. Urachal diverticula are typically asymptomatic and found during imaging for unrelated conditions. Associated anomalies, including vesicoureteral reflux, may coexist and have been reported in up to 37% of pediatric patients with urachal remnants.