In those 12 observations, without associated lesion in the brain stem, diagnosis is done 3 times at autopsy, 8 times at surgical time, and once before it, on clinical and radiographic arguments. Diagnosis must be systematically evoked in front of vestibular symptoms, before severe signs, related to intracranial hypertension and brain stem compression, become evident. Iodoventriculography (7 times) and principally computerized tomography (2 times) bring conclusive arguments for diagnosis. Those infarcts are situated 9 times in the territory of the postero-inferior cerebellar artery and 3 times in the area supplied by the antero-superior cerebellar artery. Spontaneous evolution is always lethal, but prognosis after surgery is still severe (4 long term survivals in 9 cases) for the vascular system of those patients remains fragile.