Agreement between sonographic and pathoanatomic classifications of pediatric urachal remnants

There is ongoing debate regarding whether urachal remnants in children should be treated surgically⁽¹⁾ or conservatively⁽²⁾. Historically, all urachal anomalies were excised because the epithelial lining was assumed to be the origin of malignant transformation into urachal adenocarcinoma⁽³⁾. Regardless of the chosen treatment approach, the subtype of urachal anomaly is clinically relevant. Urachal cysts, accounting for between 52 and 75% of cases^(4,5) (Fig. 1B), and urachal sinuses, representing approximately 46% of cases⁽⁵⁾ (Fig. 1C), were frequently treated surgically due to failed conservative management. Patent urachuses (Fig. 1D) and urachal diverticula (Fig. 1A), on the other hand, had a much higher rate of spontaneous resolution: twothirds of patent urachuses and 85% of urachal diverticula resolved during observation⁽⁵⁾. According to a recent systematic review, the diagnostic imaging modality of choice for urachal remnants in children is ultrasound⁽⁶⁾, but it has never been assessed for concordance with pathoanatomic diagnosis of urachal subtypes. Therefore, the aim of this study was to investigate this aspect in order to assess the accuracy of ultrasound in guiding treatment choices.

Fig. 1.

Ultrasound appearance of urachal remnants. A. Urachal diverticulum. The caudally non-obliterated urachal duct results in an extension of the bladder dome, although it is rather small in this case due to low bladder filling (marked with a white star). B. Urachal cyst. The urachal duct is obliterated cranially and caudally, with a cyst and, occasionally, residual non-obliterated duct parts, remaining in between. C. Urachal sinus. The proximal part of the urachal duct is non-obliterated and connected to the umbilicus. D. Patent urachus. The urachal duct is persistent along its entire length

At two German pediatric surgical centers, all patients below 18 years of age treated for a urachal anomaly between 1 January 2008 and 31 December 2020 were retrospectively included. Patients were identified by the diagnosis code for urachal anomaly (ICD-10-GM Q64.4) or the procedural code for surgical treatment for a urachal anomaly (OPS 5-578.8). Based on a pre-specified data extraction sheet, we collected information on patient age, sex, symptoms, imaging modalities and results, surgical approach, and final pathologic diagnosis. All ultrasound investigations were performed by specialist pediatric radiologists.

Concordance between sonographic and pathoanatomic diagnosis was assessed by crude agreement and Cohen's kappa, which was calculated using R (version 3.5.3). Retrospective studies with anonymization at the source – extracting only non-identifiable, routinely collected information from electronic patient records that cannot be traced back to individual patients – are exempt from ethical approval in the jurisdiction of the authors.

We included 15 patients from two centers, of whom 10 were male. Their median age was 0.2 years (interquartile range: 0.05–10.7 years) and all were treated by pediatric surgeons. None of the patients were overweight or obese. A urinary tract infection or failed conservative management of a urachal anomaly was not noted in any of the patients before. In four patients, the diagnosis of a urachal remnant was incidental, identified during evaluation for an unrelated condition. Among those, with an incidental finding, the urachal anomaly was operated on concomitantly with another procedure. The remaining two patients with an incidental finding were managed conservatively. Eleven patients were symptomatic. One had pain and serous discharge at the umbilicus. Serous umbilical discharge without pain was present in another seven patients, while three patients had purulent discharge from the umbilicus. In patients with purulent discharge, fluid collections could be found in the ultrasound examination, consistent with clinically suspected inflammation. All patients with a urachal anomaly had ultrasound investigations at our centers. Ultrasound influenced the treatment in one patient who was initially suspected of having omphalitis and underwent imaging to look for abscess formation or fluid collections, but was instead diagnosed with a urachal anomaly. All eleven symptomatic patients were operated on via the open approach. Of the two operated patients with the incidental finding of urachal anomaly, one had an open and the other one a laparoscopic procedure. Non-elective surgery was necessary in two of the operated patients. Emergency surgery was performed in one patient due to abscess formation with intraperitoneal perforation, which required subsequent intestinal adhesiolysis. No postoperative complications occurred.

Urachal remnants were classified by sonography as patent urachus in six patients and urachal sinus in four patients (Tab. 1). Urachal cysts were identified sonographically in two patients and a urachal diverticulum in one patient (Tab. 1). The remaining two patients had normal ultrasound findings (Tab. 1). In one of them, the ultrasound examination was considered inconclusive due to a repeatedly empty bladder. Thus, he had voiding cysturography, which revealed a patent urachus. The final pathoanatomical diagnosis in the 13 operated patients was a patent urachus in seven patients. Four patients had urachal sinuses and two patients had urachal cysts. The distribution of anomaly subtypes was similar between patients in their first year of life and those older than one year: patent urachus was more frequent than urachal sinus, which was more common than urachal cyst (Tab. 1). The diagnosis differed between ultrasound and pathology in four cases. Two patent urachuses and one urachal sinus were classified as normal on ultrasound and one patent urachus was sonographically diagnosed as a urachal sinus. The crude agreement between ultrasound and pathoanatomic diagnosis was 70% and Cohen's κ was 0.66 (95% confidence interval: 0.3–1, z=3.83, p <0.001). Epithelial lining was found in ten resected specimen, nine of which were urothelial and one intestinal in origin.

Due to the relevant complication rate following surgery for urachal anomalies, conservative management of urachal remnants is gaining ground⁽⁶⁾. This approach is particularly favored in infants and toddlers, in whom the rate of spontaneous resolution is high⁽⁶⁾. Traditionally, urachal remnants were excised once diagnosed, but this practice has been abandoned. Its justification – the possibility of malignant transformation into urachal carcinoma – ceased to apply, as the risk of malignant transformation has been shown to be negligible⁽³⁾.

However, conservative management of a urachal anomaly requires follow-up using imaging. Ultrasound is used in approximately 90% of cases, followed by computed tomography and voiding cystourethrography, whereas other imaging modalities are rarely employed^{( 1,3,6)}. The performance of the different imaging modalities has not been evaluated, although in some studies they have been used in parallel⁽⁶⁾. Despite its widespread use, concordance between ultrasound findings and final pathoanatomic diagnosis has not been evaluated before. This aspect is of relevance because the type of urachal anomaly has been reported to determine spontaneous resolution: urachal cysts and urachal sinuses are treated via surgery more often than patent urachus or urachal diverticulum for the lack of spontaneous resolution^(4,5). In this study, we found substantial agreement between ultrasound and pathoanatomic diagnosis of the type of urachal anomaly, supporting the use of ultrasound for follow-up of urachal remnants. Nonetheless, there is a substantial limitation to our results, as all patients in our series were treated by pediatric surgeons. Patients managed by pediatric surgeons often, in 70% of cases⁽⁷⁾, present with acutely infected or symptomatic urachal remnants, which was also the case in our series. In contrast, patients treated by pediatric urologists frequently had an incidental diagnosis of a urachal anomaly, in almost 70% of cases⁽⁷⁾. This resulted in substantially different management, which was surgery in 84% of patients treated by pediatric surgeons, whereas two-thirds of patients treated by pediatric urologists were managed conservatively⁽⁷⁾. We hope that our report prompts pediatric urologists to investigate whether similar or probably even higher concordance rates can be achieved in their distinct patient populations.

Ultrasound identified the type of urachal anomaly with sufficient accuracy in our cohort; however, these findings should be corroborated in a substantially larger study.