Urachus

Urachus

The urachus is a fibrous remnant of the allantois, a canal that drains the urinary bladder of the fetus that joins and runs within the umbilical cord. After birth, the urachus usually obliterates and becomes the median umbilical ligament, a fibrous cord that runs from the bladder to the umbilicus.

Anatomy

The urachus is located in the space of Retzius, between the transversalis fascia and the peritoneum. It is a midline structure that extends from the anterior dome of the bladder to the umbilicus. In adults, it is typically a fibrous cord, but in some cases, it may remain patent or partially patent, leading to various urachal anomalies.

Diagram showing the urachus in relation to the bladder and umbilicus.

Development

During fetal development, the urachus is part of the allantois, which is involved in early fluid exchange between the embryo and the yolk sac. As the fetus develops, the allantois becomes the urachus, which eventually obliterates to form the median umbilical ligament. This process is usually complete by birth.

Urachal Anomalies

Urachal anomalies occur when the urachus fails to obliterate completely. These anomalies include:

• Patent urachus: The entire urachus remains open, creating a direct connection between the bladder and the umbilicus.
• Urachal cyst: A portion of the urachus remains open, forming a cyst.
• Vesicourachal diverticulum: The urachus remains open at the bladder end, forming a diverticulum.
• Umbilical-urachal sinus: The urachus remains open at the umbilical end, forming a sinus.

Diagram showing normal urachus and common urachal anomalies.

Clinical Significance

Urachal anomalies can lead to infections, discharge from the umbilicus, and in rare cases, urachal carcinoma. Urachal carcinoma is a rare type of cancer that arises from the urachus, often presenting with hematuria, abdominal pain, or a palpable mass.

Histological image of urachal carcinoma.

Diagnosis and Treatment

Diagnosis of urachal anomalies is typically made using imaging techniques such as ultrasound, CT scan, or MRI. Treatment depends on the type of anomaly and may involve surgical excision of the urachus or drainage of any cysts or abscesses.

CT scan showing a urachal remnant.

Related Pages

• Umbilicus
• Urinary bladder
• Allantois
• Median umbilical ligament

References

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