Sonographic Evaluation of an Urachal Remnant: A Case Report

Abstract

Urachal anomalies are rare and often identified incidentally during diagnostic imaging examinations, such as sonography. These anatomical anomalies are being detected with increasing frequency due to advancements in cross-sectional imaging. Early detection facilitates effective management and treatment options. When these anomalies go undetected and persist into adulthood, patients are at an increased risk for adverse health outcomes. Urachal anomalies have the potential to undergo pathological changes, leading to inflammation, infection, and even malignancy. Therefore, it is imperative for sonographers to be proficient in identifying and understanding sonographic characteristics of urachal abnormalities. This is crucial, given that sonography continues to be a key diagnostic technique due to its lack of radiation, cost-effectiveness, and widespread availability.

Anomalies of the urachus are rare with an estimated prevalence of 1.03% to 1.6% in the pediatric population.^1,2 In this case, a pediatric patient presented to the sonography department with an external protruding nodule at the umbilicus. In addition to sonographic evaluation of the nodule, the examination revealed the presence of an urachal remnant extending from the umbilicus to the bladder. Subsequent surgical evaluation confirmed the diagnosis, and the urachal remnant was excised. This intervention effectively mitigated the risk of potential abdominal or urinary complications and the development of malignancy in the future.

Case Report

A family physician referred a 2-year-old male for a limited abdominal sonogram to evaluate a round nodule protruding from the umbilicus. The nodule had been present since birth and had increased in size. At the time of the examination, the nodule was approximately the size of a pea. The patient’s mother denied leakage of fluid from the umbilicus and stated it did not appear to bother the patient. The sonographer evaluated the region of interest using an IU-22 ultrasound equipment system (Philips Medical, Andover, MA) equipped with a L12-5 MHz linear transducer. Corresponding to the palpable nodule, imaging revealed a small, complex, ovoid area with posterior enhancement and an absence of vascularity. The nodule measured 7.0 × 5.0 × 7.0 mm (See Figure 1). Upon further interrogation of the area, the umbilical region appeared to connect inferiorly and posteriorly toward the anterosuperior aspect of the bladder by a hypoechoic, complex, tubular extension (See Figures 2 and 3). Differential considerations included a congenital urachal anomaly, umbilical hernia, or complex cyst, such as a sebaceous cyst.

Figure 1.

A transverse sonographic image demonstrated a hypoechoic, complex, round area with posterior enhancement corresponding to the patient’s palpable lump at the umbilicus, determined to be an umbilical polyp.

Figure 2.

A sagittal sonographic image demonstrated a hypoechoic, tubular structure (arrow) extending from the anterior dome of bladder superiorly toward the umbilicus, determined to be an urachal remnant.

Figure 3.

A sagittal sonographic image demonstrated the use of color Doppler to determine the nonvascular component of the hypoechoic, tubular structure.

The primary care provider referred the patient to a urologist, who subsequently made a nonurgent referral to a pediatric general surgeon. No further imaging studies were performed for this patient. Two months following the initial sonographic examination, the patient underwent surgical intervention at a specialized pediatric hospital. During the procedure, the surgeon identified the nodule as an umbilical polyp in communication with a nonspecific type of urachal remnant. The surgeon excised the polyp, then dissected and excised the urachal remnant extending to the dome of the urinary bladder. The excised tissue was sent for pathological evaluation, but results were not made available. The patient did not experience any post-operative complications.

Discussion

The urachus is an embryological remnant that extends from the anterior dome of the urinary bladder to the umbilicus. ³ During fetal development, the bladder initially forms at the level of the umbilicus and gradually descends into the pelvis by the fourth or fifth month of gestation. ³ This downward descent of the bladder causes the urachus to stretch, resulting in the obliteration of its lumen. ⁴ Subsequently, the urachus transforms into a permanent, fibrous cord-like structure known as the median umbilical ligament. ⁴ Urachal abnormalities arise from the incomplete obliteration of the urachal channel during fetal development and manifest in various forms, depending on the extent of partial closure. The classification of urachal anomalies includes four distinct types: patent urachus, umbilical-urachal sinus, vesical-urachal diverticulum, and urachal cyst.

A patent urachus occurs when the entire urachal channel fails to obliterate. This results in a tubular connection between the umbilicus and the anterosuperior wall of the bladder, permitting communication between the bladder and the umbilicus. ³ Consequently, a significant portion of individuals with a patent urachus exhibit urinary leakage from the umbilicus. ³ Sonographically, a patent urachus is visualized as a hypoechoic, potentially complex, thickened tubular structure. This structure will be seen extending from the anterior dome of the bladder to the umbilicus along the patient’s midline. Special attention to longitudinal scan planes can facilitate the diagnosis of a patent urachus. ⁵ Although the surgeon did not classify this case as a specific type of urachal remnant, its sonographic appearance is consistent with a patent urachus. An umbilical-urachal sinus results from a blind dilation at the umbilical end where the urachal lumen fails to obliterate. ³ The umbilical-urachal sinus is characterized by patency of the urachus at the umbilical end without communication to the bladder. ³ Conversely, dilation of the urachus at the bladder end without communication to the umbilicus is termed a vesical-urachal diverticulum. ³ These dilated areas appear sonographically as hypoechoic, potentially complex, with a connection to either the umbilical end (umbilical-urachal sinus) or the bladder end (urachal diverticulum). A urachal cyst forms when the middle portion of the urachus fails to obliterate. Sonographically, a urachal cyst presents as a hypoechoic, potentially complex, round area located between the bladder and umbilicus, often with posterior enhancement.

The incidence of urachal anomalies is reported to be approximately 1 in 5,000 for adults, with a significantly lower rate of 1 in 150,000 in infants. ⁶ There is a higher prevalence observed in males compared with females. ⁶ Clinically, urachal remnants vary in their presentation. Many of these anomalies are asymptomatic and are typically identified incidentally during abdominal surgical procedures or diagnostic imaging studies. ³ Urachal remnants can undergo pathological changes, leading to complications including inflammation, infection, and even malignancy. ⁷ Patients with problematic or infected urachal remnants may present with umbilical discharge, lower abdominal pain or discomfort, fever, dysuria, hematuria, or urinary tract infection. ³ Infected urachal remnants have the potential to lead to other abdominal complications. ⁷ Song et al. ⁷ reported on a 3-month-old who presented to the emergency department with a febrile urinary tract infection and developed an intestinal obstruction, secondary to an infected urachal cyst. Song et al. ⁷ suggested that clinicians consider the possibility of infected urachal remnants in patients who present with acute abdominal symptoms. Over time, the persistence of undetected or untreated urachal anomalies can result in chronic exposure to inflammatory processes and recurrent infections. ³ This chronic inflammatory exposure thereby increases the risk of carcinogenesis. ³ This type of malignancy accounts for less than 0.5% of all urinary bladder malignancies. ⁵

Sonography is the most utilized imaging technique in the evaluation of urachal remnants. ⁵ Symptomatic patients, particularly pediatric patients, are frequently referred to sonography for initial assessment, such as the present case study. This is likely due to the accessibility, cost-effectiveness, and the nonionizing and noninvasive nature of sonography. Gleason et al. ² reported in a retrospective study that in 663 out of 721 (92%) of patients with urachal remnants, sonography was utilized. Sonography is a beneficial diagnostic tool also in consideration of the anterior location of the urachal anomalies relative to intestinal structures. ⁷ Although sonography is sensitive in detecting urachal anomalies, exact specificity rates are not consistently reported in recent literature. The specificity of sonography can vary based on several factors, including the operator’s experience, quality of the equipment, and the specific characteristics of the pathology. Therefore, sonographic findings may need corroborated with other imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI) to improve diagnostic accuracy. ³ CT and MRI can also be useful for further characterization and evaluation of potential urachal remnant complications. ³

Suspicious sonographic findings that may represent urachal carcinoma include the presence of a tumor with a soft tissue mass-like appearance. ⁸ The tumor may be heterogenous and show calcifications. ⁸ Internal vascularity may also be appreciated with the use of Doppler. ⁸

With CT, an urachal tumor may have a mixed solid-cystic or solid appearance. ⁹ Calcifications are also commonly appreciated on CT and may have varying appearances. ⁸ MRI examinations may provide a more detailed evaluation of the soft tissues and can differentiate an urachal remnant from a neoplasm, cyst, or abscess. ³

Due to their extravesical and extraperitoneal location, these urachal tumors are often clinically silent. ⁸ Hence, distant metastases from urachal carcinoma usually occur quite late. ⁸ Regardless of the imaging method used, a mass containing calcifications arising from the bladder dome should raise suspicion of malignancy until proven otherwise. ⁵ Depending on the clinical presentation and type of urachal remnant identified, an imaging-guided aspiration may be performed prior to surgical intervention. ⁵

The management and treatment approach to patients with urachal anomalies remains controversial between a conservative versus surgical approach. ⁶ In patients with symptomatic urachal remnants, surgical excision is indicated. ⁵ Some experts argue that incidentally diagnosed, asymptomatic urachal remnants may be managed nonoperatively without developing complications in the short term. ³ Although not observed in this case, studies have found that urachal remnants have a high likelihood of spontaneous resolution, especially in the first year of life. ⁶ Others maintain that persistent urachal remnants in adults may eventually become symptomatic and have an elevated risk of malignant transformation. ³ As a result, surgical intervention may also be advocated for asymptomatic patients to mitigate these risks.^5,10 While the management and treatment of urachal remnants vary depending on the individual, it is essential these anomalies are accurately detected and identified.

Conclusion

Sonography remains the diagnostic imaging technique of choice for initial assessment in evaluating umbilical lesions, especially in pediatric cases. When evaluating umbilical lesions or the urinary tract system, it is crucial for the sonographer to consider the possibility of an urachal remnant. Early detection is key to appropriate management and to reduce the risk of malignancy. When examining the abdominopelvic region, the sonographer should maintain a focused assessment between the umbilicus and the bladder to identify any potential urachal remnants.