Urachal Lesions: Unveiling the Role of Imaging in Accurate Diagnosis

Introduction

Urachus is an embryonic remnant structure formed due to the involution of the cloaca and allantois that serves as a communication channel between the developing urinary bladder and the umbilicus via the allantois. Normally, this structure obliterates by mid-gestation and transforms into a fibrous cord known as the median umbilical ligament.[1] However, incomplete involution leads to various congenital urachal anomalies, which can be detected incidentally on imaging or the patient can present with urinary symptoms or nonspecific abdominal symptoms both in the pediatric and adult population predisposing the patient to infections, inflammation, and malignancy, therefore increasing the morbidity.[2]

The incidence of urachal anomalies is 1 in 5,000 and 1 in 150,000 among adults and infants. The prevalence is higher in men than in women.[3] In a recent study among the urachal anomalies, the urachal cysts are the most common type in children, accounting for approximately 69%.[4] Among benign complications, infection is the most common pathology both in children and adults whereas malignancy occurs exclusively in adults.[5]

The objective of this article was to differentiate the various types of urachal lesions with the help of cross-sectional imaging and ultrasound (USG) to strengthen the understanding of various urachal lesions because of their clinical significance.

Urachus Anatomy and Its Embryological Development

The urachus is a vestigial remnant of embryologic development, originating from two structures: the allantois and the cloaca[1] ([Fig. 1]). The allantois emerges as an outpouching from the posterior wall of the yolk sac during the third week of gestation. The cloaca is an endoderm-lined cavity that eventually divides into the anterior urogenital sinus and the posterior rectum, through the development of the urorectal septum between the 4th and 7th weeks.[1]

Fig. 1 Illustration of embryological development of urachus.

As development progresses, the superior portion of the urogenital sinus forms the urinary bladder, particularly its dome.[2] As the fetus matures, the bladder descends into the pelvis, and the allantois involutes, gradually forming a fibromuscular cord—the urachus.[2] During normal gestational maturation (around the 4th to 5th month), the urachus should completely obliterate, becoming a fibrous cord known as the median umbilical ligament, connecting the bladder dome to the umbilicus.[1] The inferior part of the urogenital sinus forms the urethra and vaginal vestibule in females and the urethra in males.[1]

Anatomic Location

The urachus runs in the midline measuring approximately 3 to 10 cm in length and diameter of 8 to 10 mm lying within the extraperitoneal space of Retzius (the retropubic space) between the transverse fascia and the parietal peritoneum.[2] It is flanked on either side by the medial umbilical ligaments (which are remnants of the obliterated umbilical arteries).[2] Histology: The urachus typically consists of three layers: inner epithelial lining: usually transitional epithelium (similar to the bladder), but can sometimes be columnar epithelium; middle submucosal connective tissue layer; and outer muscular layer: continuation of detrusor muscle of the bladder.[1]

Persistence and Clinical Relevance

Although almost 100% of neonates have a visible urachal remnant at birth, fibrosis typically leads to its disappearance. Two-thirds of adolescents and one-third of 35-year-old adults may still retain microscopic urachal remnants.[6] When the obliteration process is incomplete, it can lead to persistent urachal anomalies that predispose individuals to urinary tract infections, abscess formation, or even rare malignancies later in life.[7]

Classification of Urachal Anomalies, Their Complications, and Mimics

Urachal anomalies are classified based on the location and extent of persistence along the urachal tract[5]:

• Patent urachus: A continuous tract between the bladder and the umbilicus, leading to urinary leakage from the navel.

• Urachal cyst: A localized cystic dilatation in the mid-portion of the urachus; both ends are obliterated.

• Umbilical-urachal sinus: A blind-ending sinus that opens at the umbilicus.

• Vesicourachal diverticulum: A focal outpouching from the anterior dome of the bladder without umbilical communication.

If left untreated, they carry a risk of significant complications, including:

• Chronic infection

• Abscess formation

• Stone (calculus) formation

• Malignant transformation, particularly into urachal adenocarcinoma[7]

Imaging Modalities for Evaluation of Urachal Anomalies

USG is the first imaging modality due to its accessibility, noninvasiveness, and absence of radiation with diagnostic accuracy of approximately 90%. Computed tomography (CT) is recommended if the USG is inconclusive or if complications (e.g., infection, malignancy) are suspected. Magnetic resonance imaging (MRI) is used for complicated cases or to assess surrounding tissue involvement.[2] Voiding cystourethrogram (VCUG), for evaluation of patent urachus to visualize direct connection from the bladder to the umbilicus. A sinogram is used to confirm a diagnosis of umbilical-urachal sinus, showing a blind-ending dilatation without bladder communication.[5]

Patent Urachus

Termed occasionally as urachal fistula; clinical features include neonates with urine leaks from the umbilicus. Can present at a later age if it is very narrow when the patient develops high pressures in the urinary bladder as in cases of bladder outlet obstruction. Pathologically, the fetal allantois fails to involute into the median umbilical ligament along its entire length from the urinary bladder to the umbilicus, demonstrated by a sinogram in which the contrast is injected retrogradely via the umbilical orifice or by VCUG using the lateral projection. On USG, using a high-frequency linear probe it appears as linear tubular structure between the urinary bladder and umbilicus ([Fig. 2A–C]).[2]

Fig. 2 Patent urachus in a young male child with complaints of urine leakage from the umbilicus: (A) Sagittal ultrasound (US) image shows an anechoic tubular structure between the superior aspect of the urinary bladder and the anterior abdominal wall (arrow). (B) Sagittal computed tomography (CT) image shows a tubular structure extending from the bladder dome to the umbilicus (arrow). (C) Illustration of patent urachus.

Urachal Cysts

Urachal cyst infection can occur at any age. Usually asymptomatic, symptoms can occur if complicated by bleeding or infection. Pathologically, the fetal allantois closes at both the umbilical and vesical ends with a patent fluid-filled intervening part. The common pathogens implicated in the infection of urachal cysts include Staphylococcus, Pseudomonas, Escherichia coli, and Streptococcus. Radiologically, the uncomplicated urachal cyst is seen as a fluid-filled cyst in the midline along the course of the urachus in the ventral wall of the abdomen between the urinary bladder and umbilicus ([Fig. 3A–D]). An infected urachal cyst appears heteroechoic on the USG, with increased attenuation values than water with a thickened wall on CT ([Fig. 4]).[8] Treatment: Intravenous antibiotic therapy and/or surgical excision. Relapse is high with drainage of cysts. Differentials for an infected urachal cyst include adenocarcinoma. Differentials for simple urachal cysts include bladder diverticulum, vitelline cyst, mesenteric cyst, Meckel diverticulum, and umbilical hernia.[2]

Fig. 3 Urachal cyst in a 20-year-old asymptomatic female: (A) Axial ultrasound image shows a small midline anechoic cyst in the anterosuperior aspect of the urinary bladder with no communication with the lumen (arrow). (B) Plain computed tomography (CT) shows fluid attenuating hypodense cyst near the anterosuperior aspect of the urinary bladder (arrow). (C) Magnetic resonance imaging (MRI) shows T2 hyperintense cyst in the anterosuperior aspect of the urinary bladder (arrow). (D) Illustration of urachal cyst.

Fig. 4 Infected urachal cyst in a 35-year-old female with complaints of lower abdominal pain and fever: Sagittal contrast computed tomography (CT) image showing a peripherally enhancing collection anterosuperior to the urinary bladder in the space of Retzius (arrow).

Umbilical-Urachal Sinus

A noncommunicating dilatation near the umbilical end of the urachus. Clinically, wet umbilicus, periumbilical pain, and periodic discharge are commonly present in children. On USG, CT, and MRI, seen as a midline thickened tubular structure extending from the umbilicus ([Fig. 5A–C]) and confirmed by sinography showing no bladder communication. CT helps in delineating the infective complications. MRI for better evaluation of infective complications and developing malignancy.[9] Due to the accumulation of cellular debris in that potential space, it predisposes to infection leading to the formation of urachal abscess ([Fig. 6]), stone formation, and malignancy. The possibility of infection should be suspected in the presence of the symptomatic triad including a midline tender infraumbilical mass, sepsis, and umbilical discharge. Though the innermost layer of the urachus is mainly composed of transitional cells, the mucinous type of adenocarcinoma is the predominant histological type probably due to metaplasia secondary to chronic inflammation. Other complications are rupture into the peritoneal cavity resulting in peritonitis and uracho-colonic fistula. Differentials for this condition include vitelline duct anomalies like Meckel's diverticulum, infected umbilical vessel, patent omphalomesenteric duct, omphalitis, and appendicitis.[10]

Fig. 5 Urachal sinus in a 40-year-old male with chronic watery discharge from the umbilicus: (A) Longitudinal ultrasound (US) image shows a blind-ending hypoechoic tubular structure just below the umbilicus with no visible bladder communication to the bladder (arrows). (B) A T2 hyperintense tract is seen in the umbilical region with an extension up to the extraperitoneal fat layer (arrow). (C) Illustration of urachal sinus.

Fig. 6 Urachal abscess in a 40-year-old female presenting with umbilical discharge, fever, and erythema: Sagittal plain computed tomography (CT) image showing soft tissue fat stranding with air pockets seen at the umbilicus, infraumbilical region, and greater omentum (arrows).

Vesicourachal Diverticulum

A focal outpouching from the anterior dome of the bladder without umbilical communication due to failure of the closure of the vesical end of the urachus. Mostly asymptomatic and is incidentally detected on CT performed for other reasons. On all imaging modalities, a midline extraluminally protruding urine-filled cystic lesion in the anterosuperior aspect of the urinary bladder with no umbilicus communication ([Fig. 7A–C]). On VCUG, it is seen as contrast reflux into the diverticulum. It may be seen in patients with chronic bladder outlet obstruction and congenital lower urinary tract obstruction. Vesicourachal diverticulum is commonly seen in infants with the prune-belly syndrome. Complications include urachal stone formation and carcinoma.[11]

Fig. 7 Vesicourachal diverticulum in a 25-year-old asymptomatic male: (A) Sagittal ultrasound (US) image shows a blind-ending midline focal protrusion extending from the bladder dome arising from its dome with no communication to the umbilicus (arrow). (B) Sagittal plain computed tomography (CT) shows an empty bladder with Foley's in situ from which an air-filled diverticular outpouching arising from the anterosuperior aspect of the urinary bladder (arrow). (C) Illustration of vesicourachal diverticulum.

Complications

The contributing factors for complications depend on age and type of urachal anomaly. The most common complication in infants is urachal remnant infection. In adults it also manifests as an infection and malignancy. Other complications are persistent urinary tract infections, umbilical granulomas, and fistulization into the adjacent bowel. Calcifications and stone formation occur in urachal cysts and the vesicourachal diverticula due to chronic urinary stasis.[12]

Neoplasms

Benign

Very rare, originates from any part of the urachus mimicking malignancy and the diagnosis is made on histopathological examination following resection. Adenomas and cystadenomas are most common. Other tumors include fibromyomas, fibromas, fibroadenomas, and hamartomas.[13]

Malignant

Urachal neoplasms are also rare, accounting for less than 1% of all bladder neoplasms. Though the innermost layer of the urachus is mainly composed of transitional cells, adenocarcinoma (80%) is the predominant histological type probably due to metaplasia secondary to chronic inflammation and malignant transformation.[7] Note that 34% of adenocarcinomas of the bladder are of urachal origin. Urachal carcinomas more commonly occur in males aged 40 and 70 years old. Clinical features include hematuria being the most common, abdominal pain, dysuria, suprapubic mass, and discharge of blood, or mucus pus from the umbilicus. Commonly occur in the juxtavesicular portion of the urachus and grows cranially. The histological types of remaining 20% neoplasms include sarcomatous, urothelial, and squamous types.[14]

On cystography it appears as a filling defect or extraneous compression at the dome of the bladder. USG is the initial imaging modality that helps in assessing the location and characteristics of the lesion. It appears as a midline heteroechoic soft-tissue mass with calcifications adjacent to the lower anterior abdominal wall ([Fig. 8A]). Cross-sectional imaging is useful for confirming the same, and the extent of the lesion for assessing metastasis and lymph node status. On CT, it may be solid, cystic, or mixed. Seen as a midline soft tissue attenuating mass lesion adjacent to the dome of the urinary bladder extending to the space of Retzius. Seventy percent of the lesions show calcifications. The calcifications can be central or peripheral, punctate, stippled, or curvilinear. A midline soft tissue mass along the course of the urachus with calcifications is pathognomonic for urachal adenocarcinoma ([Fig. 8B and C]). On MRI, the lesion appears as a heterogeneously hyperintense mass in the midline on T2-weighted imaging and shows heterogeneous enhancement following contrast injection.[15]

Fig. 8 Urachal adenocarcinoma in a 55-year-old male with increased frequency of micturition: (A) Transverse ultrasound (US) image shows a heterogeneously hypoechoic mass lesion near the dome of urinary bladder taking minimal internal vascularity (arrow). (B and C) Sagittal and axial contrast computed tomography (CT) image showing a heterogeneously enhancing mass lesion with thin rim of calcification extending from the anterosuperior aspect of the bladder and internal hypoattenuation likely corresponding to mucin content (arrows).

Urachal adenocarcinoma usually has a late presentation due to its location and, therefore, has a poor prognosis. Synchronous or metachronous tumors can occur along the urachal tract. Therefore, treatment includes aggressive surgical excision including partial cystectomy and en bloc resection of the urachal mass, urachal tract, umbilicus, and pelvic lymph nodes. It has a 5-year survival rate of 6.5 to 15% in cases of local invasion and systemic metastases.[16]

Conclusion

Accurate diagnosis of urachal anomalies relies on thorough understanding of urachal embryology, anatomy, and imaging features of urachal remnant diseases. Urachal remnant diseases if not identified and treated early can result in significant morbidity and mortality. USG serves as the primary imaging modality due to its easy accessibility and high diagnostic accuracy, with CT and MRI being used for evaluation of complications like infections and neoplasms. Specialized imaging, such as VCUG and sinography, aids in the confirmation of specific anomalies. Given the rarity of benign neoplasms and the challenge of distinguishing them from malignant lesions on imaging, pathological examination is essential for guiding appropriate surgical management and avoiding unnecessary radical interventions.

Conflict of Interest

None declared.

Ethical Approval

Not applicable (pictorial article).

Patients' Consent

Patients' consent has been obtained for [Figs. 2] to [8].

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Publication History

Article published online:
28 August 2025