Urachal carcinoma: A rare tumour with specific imaging characteristics on CT

Clinical History

A 57-year-old male patient presented with vomiting and abdominal pain, ongoing for 3-4 weeks. There was a history of significant weight loss. The patient had a previous history of poliomyositis and osteoarthritis. On examination, the patient was found to be markedly cachectic with generalised abdominal tenderness.

Imaging Findings

Plain abdominal X-ray (Fig. 1) revealed a rounded calcified pelvic lesion and a dysplastic left hip. Contrast-enhanced CT scan (Fig. 2) revealed a calcified cystic lesion seen in the anterior superior aspect of the bladder. There was no discernible fat plane between the mass and the bladder – suggesting invasion. The appearances were thought likely to represent a urachal carcinoma. Other findings included extensive ascites and omental thickening suggestive of omental cake. There were a few prominent loops of small bowel but no frank obstruction.

A flexible cystoscopy (Fig. 3) revealed a tumour mass in the dome of the bladder. A transurethral biopsy was performed to obtain a histological sample. The histology demonstrated a poorly differentiated mucinous adenocarcinoma consistent with urachal origins (minimum stage pT2).

Discussion

The urachus is a midline embryonic remnant resulting from the involution of the allantoic duct and the ventral cloaca. The urachus extends upwards from the dome of the bladder, joining it to the umbilicus [1, 2]. This embryonic structure normally involutes before birth remaining as a fibrous band (also known as the median umbilical ligament). The persistence of this structure can give rise to a variety of pathology both benign and malignant [3].

Urachal carcinoma is a rare cancer accounting for less than 0.5% of all bladder cancers. The clear majority (90%) of these lesions are adenocarcinomas [4, 5], most of these (60%) are of the mucin-producing variety known as the signet ring cell type. Urachal carcinoma is more common in men, with a median age at presentation of 57.5 years [4]. Patients may present with haematuria, a suprapubic mass, dysuria or pain; however, urachal carcinoma is often clinically silent and presents late. Disseminated malignancy at diagnosis is a common finding. Urachal tumours tend to spread by direct invasion of pelvic structures – superiorly to involve the umbilicus and inferiorly to involve the bladder wall; as well as by haematogenous spread to distant sites [5]. TNM staging is appropriate and has been demonstrated to be a good predictor of survival in urachal cancer; with overall survival for all stages reaching 62 months [4].

Urachal carcinoma tends to present with a much larger extravesical component than primary bladder cancer arising from the mucosa of the bladder apex. Differentiating urachal carcinoma from other urachal disease such as infected urachal remnants and benign urachal tumours can be problematic. Ultrasound findings such as a cystic suprapubic mass may be suggestive but non-specific. On CECT Urachal carcinoma may be mainly solid, cystic or mixed. The presence of calcification (see Fig. 2) within a mid-line supravesical mass on CT can be considered almost diagnostic of urachal carcinoma [3, 6]. A mass in the same position containing pools of low attenuation fluid (see Fig. 2) representing mucus should be considered suggestive. MRI is superior to CT for assessing local bladder wall involvement. CT is essential for complete staging.

1. Urachal cancer is a rare tumour (<0.5% of bladder tumours).
2. Distinctive imaging features on CECT include calcification and pools of low density fluid within a supravesical mass.
3. A mixture of modalities including ultrasound, CECT and MRI may be helpful. Tissue diagnosis is essential in confirming the diagnosis.

Differential Diagnosis List

Final Diagnosis

Urachal carcinoma

URL:	https://eurorad.org/case/15670
DOI:	10.1594/EURORAD/CASE.15670
ISSN:	1563-4086