Figures 1-2: 1.7 x 1.8 x 3.1 cm mass located in the midline at the anterior dome of the bladder. The mass extends anteriorly into the soft tissue and demonstrates heterogeneous low T2-weighted signal.

Figure 3: An out-pouching mass arising from the anterior dome of the bladder in the sagittal plane. The cystic mass contains heterogeneous low T2-weighted signal. Approximately 2 cm cephalad of this structure, there is an 8 mm high T2-weighted signal cystic structure that is connected to the bladder mass via a thin fibrous cord.

Figure 4: Pre-gadolinium T1 axial image demonstrates heterogeneous high T1-weighted signal within the bladder mass that is not saturated out with a fat saturation pulse.

Figure 5: The bladder mass does not appear to enhance on the post-gadolinium T1-weighted axial image.

Figure 6: Axial T1-weighted subtraction image (post-contrast minus pre-contrast) confirms that the cystic out-pouching mass does not enhance. Therefore, the heterogeneous bright T1 and dark T2 weighted signal intensities within the cystic mass may represent proteinaceous debris and/or blood products.

Urachal diverticulum and an umbilical cyst.

The urachus is a vestigial structure, representing the remnant of the embryonic allantois and cloaca. In fetal life, the allantois connects the urogential sinus with the umbilicus. Normally, the allantois is obliterated during development and is replaced by a fibrous cord known as the urachus. The urachus persists as a midline structure that extends from the bladder dome to the umbilicus and is called the median umbilical ligament.

Failure of normal closure of the urachus results in a variety of urachal abnormalities. These include a patent urachus resulting from complete failure closure; a urachal sinus (which drains to the umbilicus) resulting from partial failure of closure; a urachal cyst resulting from failure of closure of the urachus near the bladder attachment; or an umbilical cyst resulting from failure of closure at the umbilical attachment.

A patent urachus commonly presents with urine draining from the umbilicus. A urachal sinus may present as a draining umbilical sinus. Urachal cysts and diverticula are usually clinically silent and often present during adulthood as incidental findings or because of infection, stones, or adenocarcinoma. Neoplastic involvement of the urachus is rare but it can extend anywhere along the course of the urachus. Urachal tumors arise most commonly from the umbilical segment (90%). Urachal tumors have a poor prognosis since they are usually advanced at presentation. Mucin-producing adenocarcinomas account for the majority of urachal tumors and occur secondary to metaplasia of transitional epithelium lining the urachus. The remainder of urachal tumors include clear cell carcinoma, transitional cell carcinomas, and urachal sarcomas.

References:

1. Dunnick, N Reed. Textbook of Uroradiology, 3rd Edition. Philadelphia: Lippincott Williams & Wilkins, 2001.
2. Semelka, Richard. Abdominal-Pelvic MRI. New York: Wiley-Liss Inc, 2002.