A 74-year-old man presented to the emergency department with hypogastric pain, fever and dysuria of 48 hours' duration. His personal history included hypertension treated with captopril, hyperlipidaemia treated with atorvastatin and hyperuricaemia treated with allopurinol. Physical examination revealed a palpable, painful, large mass occupying the hypogastrium and both iliac fossae. Blood tests showed 25,930 leukocytes with a marked left shift and urinary sediment analysis showed 3-5 leukocytes/field, microhaematuria with positive nitrites in the dipstick. An abdominal ultrasound was requested, which revealed a possible abscess in the hypogastrium measuring 15 x 9.2 x 7.3 cm. The study was completed with an abdominal-pelvic CT scan showing an image with a liquid level measuring 15 x 9 x 9 x 8 cm in the hypogastrium, above the bladder dome, in close relation to the ileocecal area, compatible with an abscess added to a benign or malignant neoformative process in the area.

With the diagnostic hypothesis of an infected urachal cyst, percutaneous drainage was performed and samples were taken for microbiology and broad-spectrum intravenous antibiotic therapy was started. Serial cultures isolated Leuconostoc spp, Streptococcus intermedius, Clostridium perfringens, Escherichia coli, Bacteroides ovatus, Corynebacterium spp. and Pseudomonas aeruginosa.
During admission, the study was completed with a new CT scan, which provided no new information with respect to the previous one; opaque enema, which provided no information on the origin of the symptoms; colonoscopy, which showed no alteration at the colonic level; and cystoscopy, in which the bladder mucosa was observed to be intact.
Once the study was completed, an exploratory laparotomy of the lesion was decided. After performing a median laparotomy, an independent bladder mass was observed, intensely adhered to the intestinal loops and cecum.

It was excised and accidentally opened, with mucoid material coming out, which was sent for intraoperative anatomical-pathological study, ruling out malignancy. An ilio-ceco-appendicular lymphadenectomy was then performed (with an intraoperative freezing diagnosis of absence of malignancy) and segmental appendico-cecal resection. The final pathological diagnosis was appendicular mucinous cystadenoma (mucocele).
The postoperative period was favourable, except for infection of the surgical wound, and the patient was discharged one month after the operation. The patient lived an independent life and was asymptomatic until one year after surgery, when he died of sudden cardiac death.

