Multimodal and serial MRI monitors brain peri-hematomal injury and repair mechanisms after experimental intracerebral hemorrhage

The peri-hematomal area (PHA) emerges as a key but puzzling interface where edematous and neuroinflammatory events co-occur after intracerebral hemorrhage (ICH), while being considered either as deleterious or protective. We aimed at unraveling the pathogeny and natural history of PHA over time after experimental ICH. Male and female rats were longitudinally followed up to day 7 using multimodal brain MRI. MRI measures were compared to neuropathological and behavioural results. While the peak of PHA volume at day 3 was predictive for spontaneous locomotor deficit without sex-effect, its drop at day 7 fitted with locomotor recovery and hematoma resorption. The PHA highest water density was observed at onset despite microvascular hypoperfusion, taken over by blood-brain barrier (BBB) leakage at day 3. Water density dropped at day 7, when vascular integrity was normalized, and the highest number of reactive astrocytes, microglial cells, and siderophages found. This study shows that the PHA with edematous component is hematoma-driven at onset and BBB-driven at day 3, but this excess neuroinflammation enabled PHA volume reduction and significant hematoma resorption as soon as day 7. Therapeutic interventions should consider this pathogeny, and be monitored by multimodal MRI in preclinical ICH models.