Specific Imaging Findings

Hemorrhagic cortical contusions on CT appear as ovoid hyperdensities centered at a gyral surface, characteristically located in the antero-inferior frontal and temporal lobes. It may be quite difficult to differentiate small contusions from streak artifacts and multiplanar reconstructions from spiral acquisitions can be very helpful. Early nonhemorrhagic contusions appear as very subtle hypodensities, but generally become conspicuous days later when significant edema develops. Hemorrhagic contusions often increase in size within the first 48 h, and nonhemorrhagic contusions can develop delayed hemorrhage. As hemorrhage and edema resolve over several weeks, contusions become less conspicuous but may leave a region of hypodense encephalomalacia. On MRI, nonhemorrhagic contusions are T1 hypointense and T2 hyperintense, usually with reduced diffusion. Acute hemorrhagic contusions will appear T1 isointense and T2 hypointense with a surrounding halo of edema, which often increases during the first week. T2*-weighted imaging better shows small hemorrhages as dark lesions. Contusions follow evolution of intraaxial hematomas and marginal enhancement can also be seen. Lesions can exhibit persistent high T1 and T2 signal for up to a year with a peripheral rim of low signal caused by hemosiderin and ferritin. Encephalomalacia with surrounding gliosis, best seen on FLAIR images as peripheral CSF-like intensity with subjacent hyperintensity, is the hallmark of contusions in the chronic stage.