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Genitourinary Imaging

Imaging of the Urachus

Published Online:Apr 10 2025https://doi.org/10.1148/rg.240122

Abstract

Frequently overlooked yet clinically significant, the urachus can exhibit a diverse range of pathologic conditions, which can pose a diagnostic challenge at imaging for the radiologist and which require a thorough understanding of urachal embryogenesis.

The urachus is a remnant fibrous cord of the allantois and the ventral aspect of the cloaca that connects the urinary bladder to the anterior abdominal wall at the level of the umbilicus. The authors explore the embryologic origins of the urachus and delineate its normal anatomy, followed by a discussion of urachal pathologic conditions seen with different imaging modalities—including US, CT, and MRI—using a case-based approach. Although it is a vestigial structure, the urachus can harbor significant disease, including congenital anomalies arising secondary to varying degrees of incomplete involution of the urachus and ranging from focal patency (urachal cyst, diverticulum, and sinus) to complete patency (patent urachus). The spectrum of congenital abnormalities can manifest with various clinical findings and is often discovered at imaging when infected. Understanding the embryogenesis of the urachus is therefore crucial for understanding the imaging manifestations of urachal abnormalities. Nonneoplastic urachal masses can be inflammatory and sometimes difficult to differentiate from malignancy. In women, the urachus can be involved by endometriosis. Neoplastic urachal entities can include mucinous cystadenoma, which can rupture with associated mucinous ascites. Adenocarcinoma is the most common urachal malignancy and frequently can extend to involve the urinary bladder. Other malignant urachal entities include urothelial carcinoma and metastasis. Mimics of urachal pathologic conditions can cause diagnostic misperception and include primary bladder malignancy, infections, and dropped gallstones or appendicoliths. This comprehensive overview aims to enhance radiologists’ proficiency in recognizing and interpreting urachal abnormalities, thus contributing to improved patient outcomes.

©RSNA, 2025

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Article History

Received: Apr 17 2024
Revision requested: May 23 2024
Revision received: July 4 2024
Accepted: July 9 2024
Published online: Apr 10 2025