Magnetic resonance imaging was performed on an eight-year-old, neutered female German Shepherd dog with a history of acute depression, inappetence, and hyperthermia. A lesion in the cerebrum was suspected. Possible differential diagnoses were meningoencephalitis, neoplasia, and vascular lesion (infarction, bleeding). A ring enhancing lesion was found in the basal ganglia on the left side with edema of the surrounding brain tissue. A similar mass lesion was present in the right pterygoid musculature. With inversion recovery sequences an altered composition of the cerebrospinal fluid (CSF) in the left lateral ventricle could be detected. CSF analysis confirmed a pyocephalus, probably due to rupture of a brain abscess into the left lateral ventricle.