The urachus, developmentally is the upper part of the bladder, both of which arise from the ventral part of the cloaca [3]. Descent of the bladder from the 5th month of development into the foetal pelvis pulls the urachus with it resulting in the formation of the urachal canal. The lumen of this canal progressively obliterates during foetal life, with eventual formation of a fibrous tract in early adult life.
At the end of development, the urachus lies between the transversalis fascia anteriorly and the peritoneum posteriorly (space of Retzius), surrounded by loose areolar tissue and attaches the umbilicus to the dome of the bladder. Histologically, it is composed of 3 layers; an innermost layer of modified transitional epithelium similar to the urothelium, the middle layer of fibroconnective tissue and outermost layer of smooth muscle continuous with the detrusor [1, 3].
There are five types of urachal abnormalities: 1) patent urachus, in which the entire tubular structure fails to close; 2) urachal cyst, in which both ends of the canal close leaving an open central portion; 3) urachal sinus, which drains proximally into the umbilicus; 4) vesicourachal diverticulum, where the distal communication to the bladder persists; and 5) alternating sinus, which can drain to either bladder or umbilicus.
The incidence of UC in adults is unknown but it is rare. It is more common in men than women [2, 4]. In a 31-year review, Risher et al [2] found 12 adults with urachal anomalies, of which 5 were UC. Modes of presentation of urachal anomalies in adults differ from those seen in children. In adults, the commonest variety is urachal cyst, with infection being usual mode of presentation [2, 5]. The route of infection is haematogenous, lymphatic, direct or ascending from the bladder. The commonly cultured microorganisms from the cystic fluid include Escherichia coli, Enterococcus faecium, Klebsiella pneumonia, Proteus, Streptococcus viridans and Fusobacterium[4, 5]. In our case, Bacteroides sp was cultured.
The clinical signs and symptoms are non-specific, as UC are largely asymptomatic until they become infected. However, the presence of the triad of symptoms including a tender midline infraumbilical mass, umbilical discharge and sepsis should arouse suspicion of UC. If left untreated, UC slowly enlarges and may drain through the umbilicus as was seen in our patient, or drain into the bladder or both, resulting in alternating sinus.
Ultrasound scan can help to make diagnosis in 77% of patients [5]. In our case, ultrasound scan was not specific and MRI scan was used to make diagnosis and define the relationship to surrounding structures.
UC can be complicated by rupture into the peritoneal cavity leading to peritonitis. Other reported complications include uracho-colonic fistula, stone formation and neoplastic transformation [6]-[9]. The risk of urachal malignancy in adults is high and the prognosis is poor. Ashley et al [4] in a 54 year retrospective study of 130 adults with urachal abnormalities found that 51% were malignant and 20% presented with metastatic disease. The median age at presentation was 61 years and the 2 common risk factors for malignancy were age and haematuria.
Although histologically, the innermost layer of the urachus is mainly transitional cell, adenocarcinoma is the predominant histological type and most are mucinous. This is probably due to metaplasia arising from chronic inflammation.
The treatment of choice for urachal cyst is by complete primary excision. An earlier report suggests a single stage procedure backed with appropriate antibiotic therapy for the treatment of infected UC [10]. However, Yoo et al [5] in their study suggested a 2 stage procedure involving initial incision and drainage, followed by later excision of the urachal remnant. In our case, we adopted a staggered plan of management. Firstly, with administration of broad spectrum antibiotics guided by microbiology sensitivity, and after resolution of sepsis interval primary excision of the cyst, including insertion of a covering corrugated wound drain.
