John R. Gaughen, Jr., M.D.

June 23, 2005

Discussion

During embryologic development, the allantois involutes to form the urachus, which extends from the apex of the bladder to the umbilicus. Normally, the urachus involutes to form a fibrous remnant. Failure of the urachus to close completely leads to a spectrum of congenital abnormalities. When the entire tract remains patent (the most common anomaly), a patent urachus is formed, which represents a fistula between the bladder and the skin surface at the umbilicus. An urachal sinus occurs when the umbilical end of the tract remains patent. A vesicourachal diverticulum occurs when the vesical end of the tract remains patent. An urachal cyst occurs when the mid-portion of the tract remains patent, with no communication with the umbilical or vesical end. Aside from a patent urachus, most urachal anomalies are asymptomatic. The most common complication is infection. Neoplasm represents an uncommon complication of urachal anomalies. Malignant neoplasms are more common than benign neoplasms. Although, like the bladder, the urachus is usually lined with transitional epithelium, the vast majority of urachal malignancies are adenocarcinoma, likely secondary to columnar metaplasia of the transitional epithelium. Both calcification and mucin production are common. Squamous cell, transitional cell, and anaplastic carcinomas comprise a small minority of urachal malignancies. Urachal adenocarcinoma peaks in middle age, usually arising at the vesical end of the tract, adjacent to the bladder. Like other precariously placed malignancies, symptoms are delayed, and patients often present in advanced stages of disease. Thus, long-term survival is poor.

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