We present the case of a five-month-old female infant who consulted for progressive irritability over a ten-day period. She presented with isolated vomiting, without fever or changes in urine or stools. In the last few days she began to have abdominal distension and on the same day of the consultation she presented with an expulsion of purulent exudate through the umbilicus, for which reason she was referred from the Primary Care Department to the Emergency Department.
She was a full-term newborn with an appropriate weight for gestational age. She had a controlled pregnancy, with no infectious risk factors. The neonatal period was uneventful.
Of note was omphalorhexis at 14 days of life, with a small residual granuloma that required cauterisation with silver nitrate on two occasions. There was no history of wet umbilicus.
On arrival at the emergency department, the physical examination revealed a red tumour with spontaneous expulsion of pus in the umbilicus. The adjacent area was shiny and distended, with no erythema or other inflammatory signs. The rest of the examination was compatible with normality. Vital signs were: temperature 36.1 °C, heart rate 139 bpm, blood pressure 98/51 mmHg and oxygen saturation 100% on room air.

An analytical control was carried out with a haemogram, showing leukocytosis with normal formula and biochemistry with C-reactive protein (CRP) of 44 mg/l. A sample of umbilical exudate was collected for culture and intravenous antibiotic treatment was started with cloxacillin and gentamicin.
Twenty-four hours after admission, an ultrasound scan of the abdomen showed a heterogeneous collection measuring 5.5 × 2.5 × 2.4 cm adjacent to the upper area of the bladder towards the umbilicus, with a diagnosis of a probable infected urachal cyst. Subsequently, Staphycoccus aureus was isolated in exudate culture, and treatment with cloxacillin was maintained, with good evolution, disappearance of inflammatory signs and purulent secretion. She was discharged six days after admission, with follow-up by Paediatric Surgery.

