http://radiographics.rsna.org/content/21/2/451.full
Jeong-Sik Yu, MD ; Ki Whang Kim, MD ; Hwa-Jin Lee, MD ; Young-Jun Lee, MD ; Choon-Sik Yoon, MD ; Myung-Joon Kim, MD

1 From the Department of Diagnostic Radiology and the Research Institute of Radiological Science, Yonsei University College of Medicine, YongDong Severance Hospital, 146-92 Dogok-Dong, Gangnam-Gu, Seoul 135-270, South Korea. Presented as a scientific exhibit at the 1999 RSNA scientific assembly. Received March 21, 2000; revision requested June 8 and received June 28; accepted June 29.

Computed tomography (CT) and ultrasonography (US) are ideally suited for demonstrating urachal remnant diseases. A patent urachus is demonstrated at longitudinal US and occasionally at CT as a tubular connection between the anterosuperior aspect of the bladder and the umbilicus. An umbilical-urachal sinus manifests at US as a thickened tubular structure along the midline below the umbilicus. A vesicourachal diverticulum is usually discovered incidentally at axial CT, appearing as a midline cystic lesion just above the anterosuperior aspect of the bladder. At US, it manifests as an extraluminally protruding, fluid-filled sac that does not communicate with the umbilicus. Urachal cysts manifest at both modalities as a noncommunicating, fluid-filled cavity in the midline lower abdominal wall located just beneath the umbilicus or above the bladder. Both infected urachal cysts and urachal carcinomas commonly display increased echogenicity at US and thick-walled cystic or mixed attenuation at CT, making it difficult to differentiate between them. Percutaneous needle biopsy or fluid aspiration is usually needed for diagnosis and therapeutic planning. Nevertheless, CT and US can help identify most disease entities originating from the urachal remnant in the anterior abdominal wall. Understanding the anatomy and the imaging features of urachal remnant diseases is essential for correct diagnosis and proper management.