EXPRESS: A Critical Review of Perihematomal Edema in Intracerebral Hemorrhage - revisiting dogma.

BACKGROUND: Perihematomal (PH) edema (PHE) is an unvarying sequel of intracerebral hemorrhage (ICH). In contrast to cerebral ischemia, wherein the consequences of edema are incontrovertible, the effects of PHE on clinical outcome after ICH are uncertain. METHODS: We performed a critical review of publications on the natural history of PHE. RESULTS: We review mechanisms of formation, including clot contraction during the hyperacute phase, and the prognostic utility of PHE. Although data support the hypothesis that PHE adversely affects clinical outcome, data interpretation is hampered by key factors: (1) Since PHE is formed by clot contraction that releases serum (interstitial edema), and blood-brain barrier dysfunction that releases plasma (vasogenic edema), PHE quantification is complex. (2) Although the apparent diffusion coefficient (ADC) is touted as distinguishing vasogenic from cytotoxic (cellular) edema, cellular changes that decrease ADC can be masked by increases in extracellular fluid. (3) Decreased ADC occurs with cytotoxic edema as well as other conditions with increased cellular water, including glial activation, inflammatory cell infiltration and heme degradation products. (4) Decreased ADC often is attributed to tissue ischemia, but assessments have largely failed to demonstrate severe ischemia of PH tissues. CONCLUSION: PHE is an acceptable predictor of outcome in ICH.