False-negative diffusion-weighted MRI in acute cerebellar stroke.

OBJECTIVE: To heighten physician awareness of false-negative diffusion-weighted (DW) magnetic-resonance imaging findings in patients with acute cerebellar infarction and the importance of periodically observing nystagmus after symptom onset.
METHODS: Between April 2007 and March 2010, we retrospectively reviewed the medical records of eight patients who had all complained of severe isolated vertigo or dizziness, and had visited an emergency department within 2-6h of its onset. Intracranial findings on initial magnetic resonance imaging (MRI) were normal. All patients had consulted our department for peripheral vestibular disorders. We periodically observed spontaneous and positional nystagmus 6-24h after symptom onset.
RESULTS: In three of the patients, the direction and/or type of nystagmus changed periodically. In four of the patients, severe vertigo, nausea, and vomiting persisted after the nystagmus had been resolved. A repeat MR examination was performed 24h after symptom onset because of the atypical pattern of nystagmus for benign peripheral vestibular disorders, at which point cerebellar infarction was detected.
CONCLUSIONS: Physicians who examine patients with acute severe isolated vertigo or dizziness should consider the possibility of false-negative DW MRI findings in case of hyperacute ischemic stroke. It is important to observe the nystagmus periodically after onset. The MR examination should be repeated more than 24h after symptom onset in patients with an atypical pattern of nystagmus for benign peripheral vestibular disorders.