The urachus, a midline tubular structure that extends upward from the anterior dome of the bladder toward the umbilicus, is a vestigial remnant of embryonic structures (allantois and cloaca), that normally involutes during normal gestational development, remaining as a fibrous band with no known function, the median umbilical ligament (1) (Figure 1).
Urachal anomalies result from incomplete involution and persistence of embryonic urachal remnants after birth and are classified into four types, depending on the level of persistence of the embryonic urachal remnants between the urinary bladder and the umbilicus (1,2). Patent urachus (47%) is the most common type, followed by urachal cyst (30%), umbilical–urachal sinus (18%), and least commonly, vesico-urachal diverticulum (3%) (2).
The majority of patients with urachal abnormalities (except those with a patent urachus) are asymptomatic (3).
However, they may become symptomatic, including umbilical discharge, erythema, the presence of a mass, and recurrent urinary tract infections (2).
These symptoms are a result of chronic urinary stagnation, which can lead to inflammation and infection (1,2).
Left untreated, these conditions can result in significant health complications, including malignancy.
Patent urachus is characterized by a persistent tubular connection between the urinary bladder and the umbilicus.
It is commonly diagnosed in neonates with umbilical urine leakage, leading to umbilical edema and delayed cord stump healing (2).
US imaging shows a tubular fluid-filled structure, with a hypoechoic wall and anechoic lumen, between the anterosuperior aspect of the bladder and umbilicus (Figure 2).
A confident diagnosis of patent urachus can be made with fluoroscopy with a sinogram or voiding cystourethrography (VCUG) by demonstration of a contrast material–filled tract extending from the bladder to the umbilicus (1,2).
The umbilical-urachal sinus consists of a fusiform blind dilatation of the urachus at the umbilical end, with a potential space that allows the accumulation of cellular debris (2).
Usually associated with infection, it is clinically evident as inflammation or umbilical mass, with or without drainage (1,2,3).
US demonstrates a hypoechoic tubular structure extending from the umbilicus just below the anterior abdominal wall, without definite communication with the urinary bladder (Figure 3).
Sinogram is the confirmatory study.
Urachal cysts form when the umbilical and vesical ends of the urachal lumen close while an intervening lumen remains patent, forming a cystic lesion, more commonly at the lower third of the urachal tract (1,2).
Usually are small asymptomatic and detected incidentally (2).
However, patients may present with abdominal pain due to hemorrhage into the cyst, spontaneous rupture of an uninfected cyst, or intraabdominal rupture of an infected cyst, ultimately leading to the development of peritonitis(2).
On US, urachal cyst appears as a thin-walled cystic lesion with posterior acoustic enhancement along the course between the umbilicus and the urinary bladder (Figure 4).
VCUG excludes the communication of the cyst with urinary bladder.
Vesicourachal diverticulum results from an incomplete obliteration of the urachus at the bladder end, manifesting as an outpouching, which does not communicate with the umbilicus (1).
Usually have a large opening and drain well into the bladder, decreasing the frequency of complications, and therefore remaining asymptomatic (1).
On the US, vesico-urachal diverticulum appears as an extraluminal, hypoechoic outpouching arising in the anterosuperior aspect of the bladder, not communicating with the umbilicus (Figure 5).
Complications: Infection is the most common complication of urachal anomalies.
Clinical symptoms include abdominal pain and tenderness, fever, erythema, purulent urinary discharge, and occasionally a palpable mass (1).
Infection routes for bacterial migration can be lymphatic, hematogenous, or by direct extension from the bladder; Staphylococcus aureus is the most commonly isolated organism (1,2).
After the infection has cleared, complete excision of the urachal remnant can be performed, to mitigate the risk of infection recurrence and potential malignant degeneration (1).
Imaging findings include the presence of a urachal remnant with complex echogenicity on the US and heterogeneous attenuation with variable contrast enhancement with inflammation of adjacent soft tissues on CT.
Both benign and malignant tumors can develop from urachal remnants.
Benign urachal tumors are extremely rare.
The most commonly described are adenomas and cystadenomas (1).
Malignant urachal neoplasms are also rare.
Although urachal remnants are lined by urothelium, 80% of urachal cancers are adenocarcinomas, likely due to chronic urinary stasis and result in columnar metaplasia of the transitional epithelium (1).
The remaining 20% are urothelial, squamous, and sarcomatoid neoplasms (1,2).
Most of the urachal carcinomas arise in the juxtavesical portion of the urachus and extend superiorly toward the umbilicus and inferiorly through the bladder wall (1,2).
Most urachal carcinomas are clinically silent due to an extraperitoneal location in the space of Retzius and patients usually present in later stages of the disease with local invasion to surrounding structures and distant metastases (2).
Hematuria and a palpable suprapubic mass are the most commonly associated symptoms (1).
At CT imaging urachal carcinomas may present with various imaging appearances (1,2).
It usually appears as a midline heterogeneous mass, adjacent to the bladder dome, with extension into the space of Retzius, and demonstrates focal irregular wall thickening (1,2) (Figure 6).
The presence of calcifications is pathognomonic of urachal adenocarcinomas and can be seen in up to 70% of cases at the periphery of the mass (1,2).
The prognosis of urachal carcinomas is poor due to their late presentation and advanced stage with local invasion (1,2).