Excerpt from Urachal Carcinoma

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Background

Urachal carcinoma is a rare cancer accounting for less than 0.7% of bladder cancers. Commonly, urachal carcinoma arises in the dome of the urinary bladder at the vesicourachal junction. The tumor commonly invades the anterior abdominal wall, and most patients have a poor prognosis. Approximately 85% of urachal carcinomas are adenocarcinomas, and these are 40% of bladder adenocarcinomas.

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Pathophysiology

The pathogenesis of urachal carcinoma is poorly understood. Adenocarcinoma is believed to arise from malignant transformation of columnar metaplasia in as many as 84% of patients. However, in 3%, it arises within the transitional cell epithelium, and the transitional epithelium undergoes metaplasia to become glandular epithelium. Approximately 70% of urachal carcinomas are mucin-producing adenocarcinomas, and 15% are non–mucin-producing adenocarcinomas.

Frequency

United States

Urachal carcinomas are rare.

Mortality/Morbidity

Mortality is based on the stage at presentation. The prognosis with urachal carcinoma is poor compared with that of other types of bladder carcinomas. Early detection is important in preventing death because urachal cancers that are found early have a good prognosis. However, in 50% of patients, the disease is fatal. The 5-year survival rate of less than 16%. The poor prognosis is a result of the late presentation of symptoms, a tendency for early local invasion, and pulmonary and osseous metastasis.

Sex

Approximately 75% of urachal carcinoma cases occur in men.

Age

Patients usually are aged 40-70 years.

Anatomy

The urachus is a musculofibrous band that is an extension of the urogenital sinus. This band extends from the bladder dome to the umbilicus; in the fetus, it is contiguous with the allantois. The urachus lies in the space of Retzius, between the transversalis fascia anteriorly and the peritoneum posteriorly. In 70% of adults, a small lumen lined by transitional epithelium remains in the urachus. The persistence of a urachal lumen can lead to a urachal fistula, urachal cyst, or urachal sinus. In some patients, this epithelium can undergo metaplasia to become glandular epithelium. The result may be malignancy, usually mucinous adenocarcinoma. Most (90%) urachal carcinomas are juxtavesical, specifically, supravesical, anterior to the bladder, or in its midline.

Clinical Details

Patients can have mucous micturition, although this occurs in only 25% of patients. More commonly, hematuria is present in as many as 75% of patients. Uncommonly, blood, pus, or mucus can drain from the umbilicus. Nonspecific abdominal pain is often a symptom.

Preferred Examination

CT is the best modality to depict urachal carcinoma, although MRI can be helpful in select patients. MRI is helpful for the evaluation of the fluid or mucous content of the urachal segment and for multiplanar depiction of the carcinoma. In most cases, CT is sufficient.

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