Urachal remnant malignancy. CT and MRI findings

Clinical History

A 79 years old male patient with lower abdominal discomfort and two episodes of gross hematuria in the last 2 weeks.

Imaging Findings

A 79 year old male patient presented to our department for a CT examination due to two episodes of gross hematuria in the last two weeks. Patient’s history was unremarkable with no urinary problems until now. On clinical examination a slight tenderness was revealed during palpation at the anterior aspect (midline) of the lower abdominal wall. Plain radiography of the abdomen was unremarkable. Ultrasound examination elsewhere (not showed) revealed mild thickening of the anterosuperior wall of the urinary bladder and a midline located mass of 4cm maximum diameter and mixed echogenicity protruding mainly extraluminaly. CT examination of the pelvis demonstrated a soft tissue mass (3.5x2.9x1.7cm) at the anterosuperior border of the urinary bladder with mild enhancement (Fig 1). No pelvic lymph node enlargement was present. The patients underwent also an MRI examination, which revealed a mass with intermediate signal intensity in T1-weighted images, moderate high signal intensity in T2-weighted images and mild enhancement after contrast medium injection (Fig 2). Lung CT and bone scan were also negative for metastatic disease. The patient underwent cystoscopy and finally total resection of the lesion with partial cystectomy. Histopathologic examination of the mass revealed a moderately differentiated adenocarcinoma of the urachal remnant.

Discussion

Urachus is a midline remnant of the intraembryonic portion of allantois [1,2]. In late foetal life (4-5th month), the urachus usually deteriorates to a thick fibrous cord (extending from the dome of the bladder to the umbilicus), also known in the adults as the median umbilical ligament [1,2,3]. An umbilical-urachal sinus, vesicourachal diverticulum or urachal cyst may close normally after birth, but then reopen in association with pathological conditions [3].
The urachus lies in the extraperitoneal space of Retzius and is bounded by the transverse fascia ventrally and the parietal peritoneum dorsally [1,3]. The urachus presents intramucosal, intramuscular, and supravesical segments. It composes from 3 distinct tissue layers: the innermost layer being lined with transitional epithelium in 70% of cases and with columnar epithelium in 30%, a middle submucosal layer of connective tissue, and the outer layer of smooth muscles and in continuum with the detrusor muscle [4].
Incomplete regression of the urachus results in four types of congenital anomalies: patent urachus, umbilical-urachal fistula, vesicourachal diverticulum, and urachal cyst (30%). Infection, benign neoplasms (adenomas, fibromas, fibroadenomas, fibromyomas, and hamartomas) and carcinomas mainly involve the urachal remnant [1]. Differentiation of inflammatory conditions from carcinoma is difficult as both can present as a solid mass with adjacent organ involvement [3].
Urachal carcinomas have a male predilection and are found in adults who are between 40-70 years old [1,6]. Although urachal remnant is lined with urothelium most tumours are adenocarcinomas due to metaplasia of transitional epithelium into columnar followed by malignant transformation [1]. Adenocarcinoma of the bladder is a rare tumour and 34% of them are urachal in origin. Most of urachal carcinomas arise in the juxtavesicular portion of the urachus and are usually midline [1,5]. However, a small deviation to the left or right of the midline may be present [5].
Clinically it presents with mucusuria, hematuria, lower urinary tract symptoms, abdominal pain, discharge of blood, pus or mucus from the umbilicus and a palpable suprapubic mass [1,6]. Mucusuria merits special attention as it may be overlooked for a long time before the correct diagnosis, as it is usually misinterpreted for lower urinary tract infections (urethritis, chronic prostatitis) [6].
US demonstrates a midline mass of mixed echogenicity. Calcifications may be also present. CT reveals a midline enhancing mass at the anterosuperior border of the urinary bladder. Calcifications in the mass due to mucus production are encountered in 72% of cases. When present, they are considered pathognomonic for urachal adenocarcinoma [1,6]. MRI due to the advantage of multiplanar imaging is useful in determining the involvement of the urinary bladder or of other adjacent structures. Due to mucus production from the lesion, it presents with high-signal intensity in T2 weighted images.
Treatment consists of open radical or partial cystectomy with pelvic lymph node dissection, and excision of the umbilicus and the urachal ligament. Metastatic disease has poor response to chemotherapy. Overall survival for all stages is 62 months with a 34% of the patients still alive after 5 years [6].

Differential Diagnosis List

Final Diagnosis

Urachal remnant adenocarcinoma.

URL:	https://eurorad.org/case/7549
DOI:	10.1594/EURORAD/CASE.7549
ISSN:	1563-4086