To the best of our knowledge, this is the first study to demonstrate the incidence of urachal remnants in children using laparoscopic visualization as well as its distribution by age. There are several reports regarding the incidence of urachal remnants detected by ultrasonography, which range from 1.0–61.7% of symptomatic patients [4, 8, 15]. As the clinical signs and symptoms of urachal remnants may be nonspecific and misleading, the accurate diagnosis of urachal remnant disease can be challenging [6]. A detailed history, careful examination, and knowledge of the embryologic anatomy as well as excellent ultrasonography expertise are essential for accurate diagnosis [6, 7]. Additionally, anatomic variants of urachal remnants that turn laterally toward one of the lateral umbilical ligaments, as shown in our results, make detection more difficult. The difficulty of ultrasonographic urachal remnant diagnosis even in symptomatic children, suggests that its use in asymptomatic children may be even more challenging. We therefore consider data regarding the incidence of urachal remnants obtained by laparoscopic view to be more accurate than that obtained via ultrasonography.
In an autopsy study of a random group of 122 adults (aged greater than 38 years), Schubert et al. noted that 32% of bladders exhibited tubular urachal remnants [16]. Our findings demonstrated that the incidence rate of urachal remnants in the group aged ≥ 6 years was 31.7%, which was significantly lower than in the group aged < 1 year, but not significantly different to the incidence in the groups aged ≥ 1 to < 3 and ≥ 3 to < 6 years. The incidence in children aged ≥ 6 years was almost the same as that reported previously in adults by Schubert et al. [16] and suggests that the involution of urachal remnants is usually completed by the age of 1 year. The high incidence rate of urachal remnants as well as its probable spontaneous resolution by the age of 1 year, suggests that children with asymptomatic urachal remnants do not require follow-up, and that especially those under 1 year of age do not require surgical resection unless they develop multiple symptomatic episodes.
The possibility of malignancy arising from urachal remnants is still debatable. Pinthus et al. demonstrated that urachal adenocarcinoma has an estimated incidence of 0.18 per 100,000 individuals per year [17]. Therefore, Gleason et al. found that from their incidence data of 1.03%, 5721 urachal remnants would need to be excised to prevent a single case of urachal adenocarcinoma, calculated as the annual incidence of urachal adenocarcinoma in the general population with urachal remnants (1030 per 100,000) divided by the annual incidence of urachal adenocarcinoma in the general population (0.18 per 100,000) [4]. They conclude that prophylactic excision for children with asymptomatic lesions is not required. In the same estimation of the number needed to treat from our incidence data of 35.5%, 197,222 urachal remnants would need to be excised to prevent a single case of urachal adenocarcinoma. This suggests that the risk of malignancy in urachal remnants is considerably lower than previously thought. As the probability of developing malignancy is extremely low, we also recommend that asymptomatic urachal remnants, most of which are found incidentally, not be excised.
Among our 140 cases with urachal remnants, 49 cases had an unusual anatomic variant (types 2–4). There are a few reports of unusual localizations of urachal remnants that deviate from the midline, and that presented as a urachal sinus [18] or a cyst [19]. Our results support these findings. Knowledge of these anatomic variants could improve the accuracy of diagnosis of urachal remnants. There are a few reports on the infection of a lateral umbilical ligament [20, 21]. However, from our data of the anatomical variants as well as previous case reports [18, 19], these cases of infected lateral umbilical ligaments might in fact originate from urachal remnants.
In our case of the surgical excision of a urachal remnant, its path was visualized using a laparoscopic view, which aided with its excision. Therefore, even though total excision via an umbilical incision alone can be performed in young children, initial confirmation of the localization of the urachal remnant by laparoscopy is recommended for accurate and complete excision in order to prevent recurrence.
There are two main limitations to this study. First, the study subjects all had inguinal hernias. However, as far as we are aware, there have been no reports of an association between urachal remnants and inguinal hernias. We thus consider that the study subjects were appropriate. Secondly, microscopic patency could not be confirmed in the urachal structures. According to the literature by Schubert, et al. [16], even though macroscopically patent urachal structures were not observed in the 122 autopsies, 32% (39/122) showed tubular urachal remnants with preserved epithelium on microscopic examination, of which 68.4% had a lumen covered with transitional epithelium and the remainder had columnar epithelium. In fact, the patient examined in the present study, with a urachal diverticulum, who underwent urachal remnant excision, also had a microscopic lumen covered with mixed transitional epithelium and mucous columnar epithelium in the urachal cord on histopathological examination. Therefore, we predict that the urachal structures in this study have a microscopic lumen, although in order to further elucidate this, research targeting pediatric autopsies would be required.
In conclusion, urachal remnants appear to be much more common than previously reported. Most patients with asymptomatic lesions do not appear to benefit from excision. Nevertheless, each child should be assessed individually and the presence of repeated symptoms considered. Our data indicate a recommendation of nonoperative management of asymptomatic urachal remnants, especially in patients less than 1 year old. Knowledge of the anatomic variants could improve the accuracy of diagnosis of urachal remnants as well as provide a better understanding of its structure and localization for the achievement of accurate and complete excision.