Multimodal MRI characterization of experimental subarachnoid hemorrhage

- Subarachnoid hemorrhage (SAH) results in transient vasospasm and venous abnormality.
- SAH transiently reduces basal cerebral blood flow and its response to hypercapnia.
- SAH causes transient diffusion change but no ischemic brain injury.
- Both SAH and control rats show reduced open-field activities.
- There are however no differences in functional deficits between groups.

Subarachnoid hemorrhage (SAH) is associated with significant morbidity and mortality. We implemented an in-scanner rat model of mild SAH in which blood or vehicle was injected into the cistern magna, and applied multimodal MRI to study the brain prior to, immediately after (5 min to 4 h), and upto 7 days after SAH. Vehicle injection did not change arterial lumen diameter, apparent diffusion coefficient (ADC), T2, venous signal, vascular reactivity to hypercapnia, or foot-fault scores, but mildly reduce cerebral blood flow (CBF) up to 4 h, and open-field activity up to 7 days post injection. By contrast, blood injection caused: (i) vasospasm 30 min after SAH but not thereafter, (ii) venous abnormalities at 3 h and 2 days, delayed relative to vasospasm, (iii) reduced basal CBF and to hypercapnia 1-4 h but not thereafter, (iv) reduced ADC immediately after SAH but no ADC and T2 changes on days 2 and 7, and (v) reduced open-field activities in both SAH and vehicle animals, but no significant differences in open-field activities and foot-fault tests between groups. Mild SAH exhibited transient and mild hemodynamic disturbances and diffusion changes, but did not show apparent ischemic brain injury nor functional deficits.