Interhemispheric intracranial pressure gradients in nonhuman primate stroke

BACKGROUND: Although the development of significant interhemispheric intracranial pressure (ICP) gradients in the setting of unilateral stroke remains controversial, no study to date has investigated the existence of these gradients in a controlled, reproducible, clinically relevant model. Therefore, we used a primate model of reperfused hemispheric stroke to better characterize the development of these gradients. METHODS: Bilateral intraparenchymal ICP was continuously monitored in 7 adult male baboons subjected to left hemisphere reperfused stroke. Interhemispheric ICP gradients were calculated for each baboon and plotted over time. Infarct volume was determined using T2-weighted magnetic resonance imaging (MRI) at sacrifice. RESULTS: A bimodal distribution of interhemispheric ICP gradients was observed in animals with > 20% infarct volume (22.1% ± 0.9; range 21-23%) versus ≤ 15% infarct volume (6.6% ± 2.7; range 1-15%). In animals with > 20% infarct volume, interhemispheric gradients developed early and persisted throughout the monitoring period. At 12 hours postreperfusion, animals with large infarcts demonstrated a mean pressure gradient of 13.8 ± 4.3 mm Hg, compared to a mean gradient of -2.6 ± 1.1 mm Hg for animals with ≤15% infarct volume. The difference in pressure gradients was statistically significant at all time points from 4 to 12 hours postreperfusion (p < 0.01). CONCLUSIONS: These data suggest that, in nonhuman primates, infarcts of a size approaching 20% of the hemisphere may be associated with significant ICP gradients. With these larger infarcts, ipsilateral monitoring is required if regional cerebral perfusion pressure is to be accurately assessed.