RESUMO
An unusual association between an arachnoid cyst and a decompensated pyloric stenosis in a three years-old boy is presented. The little patient was admitted into hospital with haematemesis, melena, influenced generally condition and acute posthemorrhagic anaemia following aspirin intake for hypertermia. Specific intensive care was successful and the little patient was discharged but without an upper digestive endoscopy(parents refusal, technical reasons). After one week he returned with progressive worsening vomitings and an intracranial hypertension was suspected. CT documented an arachnoid cyst in the right middle cranial fossa and the patient is directed to the Neurosurgical Clinic where a cyst fenestration was done. Subsequent to operation the vomitings reinstaled with severe dehydration and an upper GI series showed a decompensated pyloric stenosis. He was operated on underwenting an antrectomy. Finally the child recovered with good short and long-term evolution. The coincidental presence of an intracranial congenital mass and a complicated aspirin-induced peptic ulcer in this young patient, misleaded us and in the lack of an early endoscopy an intempestive neurosurgical operation was initially done.