A 35-year-old lady in her first trimester of pregnancy presented with abdominal pain and a palpable anterior abdominopelvic mass. Ultrasound (US) of the pelvis (Fig. 63.1a, b) demonstrated a gravid uterus with multiple uterine fibroids (not shown). In addition, a hypoechoic solid mass with moderately prominent vascularity was noted superior to the uterus, extending up to the umbilicus, raising the suspicion of a pedunculated fibroid. An MRI of the pelvis (Fig. 63.1c, d) also revealed a large heterogeneously enhancing mass beneath the anterior pelvic wall, extending up to the umbilicus. The mass was resected and histopathological analysis revealed a squamous cell carcinoma of a urachal remnant. The pregnancy continued successfully to term.
The urachus is a three-layered remnant of the embryonic allantois (innermost layer of transitional epithelium, an intermediate layer of fibroconnective tissue, and outer smooth muscle layer). The urachus extends from the dome of the bladder to the umbilicus and gets progressively obliterated by four to five months of gestation, leaving behind a fibrous cord called the median umbilical ligament. The complete obliteration of the urachus was originally thought to be a prenatal process; however, recent literature has indicated that the involution may continue in the first few months of life. Failure of this obliteration may result in different types of urachal remnant anomalies, including a completely patent urachus (vesicoumbilical fistula, 48%), vesicourachal diverticulum (3%), umbilical-urachal sinus (18%), and urachal cyst (31%). A normal urachal remnant is quite commonly seen as an incidental finding on pelvic US in children as a small hypoechoic structure, superior to the urinary bladder (Fig. 63.2). A patent urachus can be seen as a tubular connection between the bladder and the umbilicus on sagittal us (Fig. 63.3). An umbilical-urachal sinus can be seen as a blind-ending midline tubular structure below the umbilicus, and may occasionally become infected, resulting in umbilical drainage. A vesicourachal diverticulum is generally asymptomatic and can be incidentally detected on imaging as a midline cystic structure at the superior aspect of the bladder. Occasionally, a large diverticulum may result in stasis, aberrant micturition, infection, or stone formation. Urachal diverticulum as well as other urachal anomalies are particularly associated with prune belly syndrome (see Case 58). A urachal cyst is formed when the urachus closes at both the umbilical and bladder ends and remains patent in between.