Clinical and MRI features of hemorrhagic transformation of an ischemic stroke in a dog

Hemorrhagic transformation (HT) is a well described complication of ischemic stroke in humans, associated with increased morbidity and mortality, secondary to blood-brain barrier disruption and reperfusion. Aim of this case report is to describe the MRI features of a clinically suspected HT after ischemic stroke in a dog. An eight-year-old female neutered mixed-breed dog presented with acute onset of intracranial clinical signs consistent with a left-sided forebrain disease. MRI, performed within 12 hours from the onset of clinical signs, revealed a large well-defined area of high diffusion-weighted imaging (DWI) signal and corresponding low apparent diffusion coefficient (ADC) map values, indicative of abnormal restricted diffusion, encompassing the majority of the vascular territory supplied by the left middle cerebral artery. The lesion was not visible in any other sequence, suggesting a peracute ischemic infarct. Cerebrospinal fluid examination was unremarkable. Concurrent medical conditions associated with the cerebrovascular accident were not identified. In the following 24 hours the dog showed severe clinical deterioration, suggesting a brainstem involvement. A 40-hour follow-up MRI revealed mixed T2-weighted hyper- and hypointense areas in the same vascular territory, different combinations of DWI signal and ADC map values, and a severe mass effect. Extensive susceptibility artifacts in Flow Sensitive Black Blood imaging were detected, indicating HT of the previous ischemic infarct. Discussion HT may represent a sequela of ischemic infarcts in dogs as described in humans. Rapid and severe clinical deterioration in a patient previously diagnosed with ischemic stroke should raise suspicion and warrant further MRI evaluation.