Introduction: The new techniques of magnetic resonance imaging have produced a important advance in the early diagnosis of acute ischemic stroke. The diffusion weighted imaging (DWI) has a high sensitivity and specificity in the acute ischemia.
Case report: 70 years old woman with previous history of hypertension and dyslipemia. The patient presented sudden vertigo with cervical neck pain and gaze problems. The physical exploration revealed right miosis, nistagmus, IX and X cranial nerve affection and ataxia. The clinical diagnosis was Wallenberg s syndrome and a medulla lateral infarction. However DWI was normal (10 hours). The neurological deficit was persistent and a repeated study disclosed a lateral infarction of the medulla.
Conclusions: The sensitivity of DWI is reduced during the first 24 hours. There are false negative diagnosis mainly in small infarctions of posterior territory.