Congenital Urachal Anomalies

Patent Urachus (Fig. 1)

This anomaly represents the complete failure of the urachal lumen to close, resulting in a persistent connection between the bladder and the umbilicus. It accounts for up to 50% of congenital urachal anomalies and is typically identified in neonates due to urinary leakage from the umbilicus. In some cases, it can also be associated with other hereditary defects like urethral atresia or posterior urethral valves.

Diagnosis can be made through imaging modalities such as ultrasonography, voiding cystourethrography (VCUG) or sinography which are the first choice in newborns.

Ocasionally, the patient can remain asymptomatic and the diagnosis is only made later in life, usually due to complications or incidentally when performing other imaging modalities for other reasons.

Urachal Cyst (Figs. 2, 3)

A urachal cyst occurs when the central portion of the urachus remains patent while the bladder and umbilical ends close. This anomaly accounts for approximately 30% of cases and is frequently located in the lower third of the urachus.

Most cysts are asymptomatic and incidentally discovered during imaging for unrelated purposes. Although uncommon, when symptomatic due to infection, they present with signs of lower abdominal pain and swelling mimicking other conditions, leading to a broad and challenging differential diagnosis. 

Ultrasonography and CT usually allow a fairly easy diagnosis, although in the context of infection, distinguishing it from a neoplasm can prove challenging.

Umbilical-Urachal Sinus (Fig. 4)

The urachus may remain open at the umbilical end forming a blind pouch. This anomaly often manifests with intermittent umbilical discharge and is prone to infection. Less commonly, it can also lead to lithiasis formation.

Imaging modalities reveal a thickened, tubular, blind-ending structure extending from the umbilicus without communication with the bladder. Sinography with retrograde filling using water-soluble contrast may be performed to confirm the diagnosis.

Urachal Diverticulum (Figs. 5, 6)

This rare anomaly results from the persistence of the bladder end of the urachus. It is generally asymptomatic and discovered incidentally, usually in patients with chronic urinary tract obstruction. It is associated with an increased risk of infection, stone formation and urachal carcinoma.  

This anomaly appears as a protruding, fluid-filled diverticular structure arising from the anterosuperior dome of the bladder. Exams where the bladder is opacified, such as cystourethrography, are particularly effective in identifying it.

Alternating Sinus

The alternating sinus is an exceedingly rare variant characterized by intermittent drainage due to partial obliteration of the urachal lumen. Its clinical and radiological features closely resemble those of the umbilical-urachal sinus.

Management

Surgical removal is the treatment of choice of urachal congenital anomalies because of the high risk of (re)infection and the potential of malignant degeneration.

Acquired Urachal Anomalies

Infections (Fig. 7)

Infections typically arise as complications of congenital anomalies and may occur via hematogenous or lymphatic spread, or through direct extension from the bladder.

Clinical Manifestations

Patients often present with lower abdominal pain, fever, dysuria, purulent discharge and, less commonly, a palpable mass. Severe cases may lead to abscess formation, complex fistulas or even peritonitis if rupture occurs. This clinical scenario is non-specific and includes a broad differential diagnosis, making diagnosis challenging.

Imaging Findings

Ultrasound is usually the initial diagnostic tool due to its availability. It tipically reveals mid-line abdominal changes with complex echogenicity. CT is frequently performed because of unclear findings on ultrasound, and it commonly depicts urachal and bladder wall thickening with surrounding fat stranding as well as heterogeneous enhancement, making differentiation from malignancy difficult.

Owing to its better soft-tissue resolution, MRI is useful in making the final diagnosis, while delineating the extent and complexity of the infection and depicting the underlying urachal anomaly.

In cases where diagnostic uncertainty persists, fluid aspiration and/or biopsy may be necessary.

Management

Treatment includes antibiotic therapy and, once the acute process resolves, complete surgical removal of the underlying urachal remnant.

Neoplasms (Figs. 8, 9, 10)

Urachal neoplasms are rare, representing about 0.5% of all bladder tumors. They are most common in middle age and elderly males.

Benign neoplasms, such as fibromas, adenomas, leiomyomas and hamartomas, are exceedingly rare and indistinguishable from malignant tumors by imaging. Diagnosis is established postoperatively via histopathologic evaluation.

In malignant urachal neoplasms, despite the urachus being lined by transitional epithelium, adenocarcinoma is the most frequent histologic subtype (often mucin-producing) which may happen due to columnar epithelium metaplasia in the setting of chronic irritation. Less common subtypes include urothelial carcinoma and sarcomas, the latter seen more frequently in younger patients.

Clinical Manifestations

These lesions are often asymptomatic until advanced stages because of their extraperitoneal location and frequently arise at the juxtavesical portion of the urachus. When symptoms do appear, hematuria and a suprapubic mass are the most common. Advanced cases may present with systemic symptoms or local invasion into adjacent structures.

Imaging Findings

Ultrasound commonly reveals a midline supravesical mass with mixed echogenicity, sometimes with calcifications which is an imaging finding that aids in distinguishing urachal tumors from other bladder pathologies.

CT demonstrates a midline mass anterosuperior to the dome of the bladder frequently demonstrating solid and cystic components, the latter corresponding to mucin components at histopathology. Calcifications are present in 50–70% of cases, whose presence in a midline supravesical mass is nearly diagnostic of urachal cancer. Unlike bladder neoplasms, urachus neoplasms tend to grow cranially toward the umbilicus.

MRI provides superior soft-tissue contrast excelling at the local staging of the disease. Images usually show a midline mass with heterogeneous high sinal intensity on T2-weighted images, due to the frequent mucinous components, although fluid collections or necrosis may also have the same appearance. Low T1-weighted signal and enhancement following contrast administration allow the distinction from fluid or necrosis and raise the conspicuity of the lesion.

Management and Prognosis

In general, the prognosis of malignant urachal neoplasms is poor since they are commonly diagnosed in advanced stages due to lack of symptoms in an early phase.

Radical excision is the primary treatment, involving partial cystectomy and en bloc removal of the urachus from the bladder dome to the umbilicus including the rectus sheath and often accompanied with pelvic lymphadenectomy.

Local recurrence is common within the first two years after treatment.