The Mechanical Penumbra in Intracerebral Hemorrhage

Penumbral imaging has profoundly changed acute ischemic stroke care by improving patient selection for acute intervention. No such innovation has occurred in intracerebral hemorrhage (ICH), despite a long debate about the existence of a penumbra in the tissue surrounding the hemorrhage. Different types of penumbrae, including an ischemic and metabolic penumbrae, have been proposed; however, we would like to draw attention to the likely existence of a mechanical penumbra that is, perilesional tissue compressed by the physical forces of the hematoma, that remains structurally intact, but recovers if the compression is relieved in a timely manner. Many ICHs occur in deep subcortical structures and compress adjacent white matter tracts. Axonal integrity is measured with diffusion tensor imaging (DTI), which may be able to estimate penumbral tissue in ICH. We propose the presence of a core and penumbra surrounding each ICH. DTI could potentially differentiate irreversibly damaged axons (core axons) from axons that remain salvageable (penumbral axons) and define the extent of a mechanical penumbra. We advocate for developing imaging biomarkers of perihematomal tissue viability to optimally select patients for surgical evacuation.