Cerebral ischemic hypoxia: Discrepancy between apparent diffusion coefficients and histologic changes in rats

PURPOSE: To compare the apparent diffusion coefficients (ADCs) and histolog ic changes in young rats subjected to cerebral ischemic hypoxia (IH). MATERIALS AND METHODS: Fifteen 3-week-old rats were subjected to a 30-minut e IH insult (unilateral common carotid arterial ligation and exposure to 8% oxygen) and were examined at diffusion-weighted magnetic resonance imaging and light and electron microscopy on cessation of the insult (n = 5), 60 m inutes after resuscitation (n = 5), or 48 hours after resuscitation (n = 5) . Twelve control rats either underwent unilateral common carotid arterial l igation or were subjected to hypoxia. RESULTS: The experimental rats showed primary ADC reduction during the insu lt, transient ADC recovery after resuscitation, and secondary ADC reduction 48 hours after the insult. Histologic examination revealed dendritic swell ing and mild swelling of the perivascular astrocytic end-feet during the pr imary ADC reduction phase, dark neurons and pronounced swelling of the peri vascular astrocytic end-feet during the transient ADC recovery phase, and s everely retracted dark neurons and extensive swelling of the astrocytic end -feet during the secondary ADC reduction phase. CONCLUSION: Transient ADC normalization after cerebral IH does not necessar ily mean that histologic normalization has occurred. The transient ADC reco very phase appeared to have limited potential for neuronal salvage.