Urachal remnant carcinoma - a rare entity
1 Department of Radiology, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa
2
Department of Surgery, Nelson R Mandela School
of Medicine, University of KwaZulu-Natal, Durban, South Africa
Primary malignancy of the urachal remnant is a rare neoplasm
that accounts for less than 0.01% of all adult cancers, with an
estimated annual incidence of 1:5 million. The tumour carries a
grave prognosis that attests to its highly aggressive nature.
Owing to its extra-peritoneal location, the tumour runs a
relatively silent clinical course until late presentation, when
most patients display extensive local invasion and metastatic
spread. In this report, we highlight a case of primary
malignancy of the urachus that on initial clinical evaluation
masqueraded as a Sister Mary Joseph’s nodule. Characteristic
imaging features, however, proved decisive in establishing the
diagnosis of a urachal carcinoma.
S
Afr J Rad
2013;17(2):63-64. DOI:10.7196/SAJR.837
A 51-year-old man presented to the surgical department with bleeding from an ulcerated umbilical mass, associated with lower abdominal discomfort and painless haematuria. Abdominal examination revealed an irregular umbilical mass with central ulceration. A provisional clinical diagnosis of a Sister Mary Joseph’s (SMJ) nodule was made. Blood results, abdominal X-rays and a barium enema study proved unremarkable in determining a primary lesion. Computed tomography (CT) of the chest and abdomen demonstrated an irregular soft-tissue mass extending from the urinary bladder dome to the umbilicus, with localised infiltration of the anterior abdominal wall and cutaneous surface (Fig. 1). The tumour displayed punctate calcification and heterogenous enhancement (Fig. 2). Bilateral pulmonary nodules were indicative of metastatic lung deposits. A voiding cystogram revealed an elongated ‘teardrop’ bladder with constant indentation and irregularity of the vesical dome suggestive of extrinsic compression with possible mural invasion (Fig. 3). A radiological diagnosis of a urachal malignancy was made. Magnetic resonance imaging (MRI) was not undertaken as it was thought to confer little benefit in the setting of advanced disease.
Following histological confirmation of moderately
differentiated invasive adenocarcinoma of the urachal remnant,
and administration of chemotherapy, the patient developed
cerebral metastasis and died within a year of diagnosis.
Fig. 1. Midline sagittal CT of the lower abdomen and pelvis demonstrates a heterogeneously enhancing soft tissue mass involving the bladder dome extending to the umbilicus with infiltration of the adjacent anterior abdominal wall (arrow). Note the elongated ‘teardrop’ bladder (circle).
Fig. 2. Axial CT image through the superior aspect of the pelvis demonstrates a midline mass at the umbilicus (thick arrow) with fine punctate calcification (thin arrow).
Fig. 3. Lateral cystogram view demonstrates irregular nodular indentation of the bladder dome (arrow) and elongated urinary bladder (circle).
Discussion
In early fetal development, the ventral cloaca (the
precursor of the fetal bladder) is connected to the allantois
via the urachus. The tubular urachus undergoes progressive
involution, resulting in an obliterated, fibrous cord by 32
weeks’ gestation. This vestigial remnant, also known as the
median umbilical ligament, extends in the midline from the
bladder apex to the umbilicus. It is located in the
extraperitoneal space of Retzius, which is bounded by the
parietal peritoneum posteriorly and the tranversalis fascia
anteriorly.1
,
2 Incomplete
regression of the urachus results in 4 recognisable anomalies,
which are indicated in Fig. 4.
Acquired urachal conditions include infection and, rarely, malignancy.1 , 2 Malignant urachal neoplasms account for less than 0.5% of all bladder malignancies, affecting mainly men of 40 - 70 years’ age. Although the urachus is normally lined by transitional epithelium, almost 90% of urachal tumours are adenocarcinomas, 75% of which are mucin producing.1 The pathophysiology is unclear; it has been proposed that metaplasia of the urachal mucosa into columnar epithelium followed by malignant transformation is the most probable aetiology.3
Patients with urachal carcinoma present with haematuria, dysuria, abdominal pain, umbilical mass or bloody, mucoid discharge.4 Urachal tumours arise in the juxtavesical portion of the urachus and extend inferiorly into the bladder and superiorly towards the umbilicus.1 Owing to its extraperitoneal location, the tumour has a silent clinical course. The late clinical presentation often delays appropriate therapeutic intervention;5 surgery is the mainstay, encompassing en bloc resection of the urachus, umbilicus, surrounding soft tissues, bilateral pelvic lymphadenectomy and partial/radical cystectomy. Radiotherapy and chemotherapy have shown no definitive success.6
Radiology plays an integral role in the diagnosis and staging of urachal malignancies. CT demonstrates a solitary midline mass located anterosuperiorly to the vesical dome, which may be solid, cystic or mixed. Heterogenous enhancement with intratumoral areas of low attenuation may be seen, representing pools of mucin or necrosis. Psammomatous calcification is a hallmark feature occuring in 50 - 70% of lesions.4 Stippled, punctate or curvilinear calcification is usually detected on the peripheral aspect of the tumour mass. CT is pivotal in tumour staging, demonstrating local extent of disease, pelvic lymph node involvement and systemic metastastic spread, commonly to lung, liver, brain or bone. Perilesional fat stranding is suggestive but not specific for malignancy as infection may display similar features.1 MRI confers similar findings to CT with regard to tumour location. The lesion is characteristically T2 hyperintense owing to the presence of intratumoural mucin. MRI also helps to determine the intravesical extent of tumour.5 On ultrasound, urachal carcinomas appear as cystic lesions with mixed echogenicity or as a solid mass. Areas of echogenicity are reflective of calcification or mucin.4
Haematuria is the most common presenting symptom in both urachal carcinoma and primary malignancy of the bladder. Considerable overlap in presentation makes it difficult to clinically differentiate between these two entities. It is imperative that optimal distinction be made as urachal carcinoma carries a worse prognosis and therapeutic management differs for both cancers. Even at cystoscopy, it is a clinical challenge to distinguish primary bladder tumour arising at the bladder apex from a urachal carcinoma. A tumour in the location of the bladder apex should alert the clinician to the possibility of a urachal malignancy and prompt further investigations. The characteristic imaging features and location of tumour assists accurate differentiation. Primary bladder carcinoma has a large intravesical component compared with urachal carcinomas that have a large extra-vesical component and a tendency to spread extraperitoneally into the space of Retzius and the umbilical region.5
Similarly to our reported case, urachal carcinoma can manifest
as a mass in the region of the umbilicus. Clinically, it can
closely resemble a SMJ nodule. Emphasis must be made that
primary urachal carcinoma and a SMJ nodule are two very
different pathologies. The eponymous nodule has been ascribed to
umbilical or para-umbilical metastatic nodules that could be the
first sign of malignancy from the gastro-intestinal tract, the
female genital tract or the genito-urinary tract. The
radiological features of the nodule differ considerably from
that of a primary urachal tumour, which is crucial in
differentiating these umbilical entities. On imaging, a SMJ
nodule appears as a discrete, well-defined mass confined to the
subcutaneous tissues or intradermal layers of the anterior
abdominal wall at the umbilical/periumbilical region. Unlike an
urachal tumour, it does not demonstrate contiguity with the
bladder dome or tumour extension along the urachal remnant.
Conclusion
Owing to its location and presentation, urachal carcinoma can
clinically mimic a SMJ nodule. A sound understanding of the
anatomy, a high index of clinical suspicion, and the
radiological features of this tumour are crucial to an accurate
diagnosis. As urachal carcinoma carries an unfavourable
prognosis, early detection and accurate staging is imperative to
expedite treatment and improve clinical outcome.
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