Specific Imaging Findings

Head CT scans obtained immediately following procedures involving intra-arterial injection of large volumes of iodinated contrast media may show parenchymal or subarachnoid space enhancement mimicking intracranial hemorrhage. The findings include diffuse parenchymal hyperintensity and increased subarachnoid space attenuation usually corresponding to the arterial territory injected, without associated gyral swelling. Occasionally, ventricular CSF may also demonstrate increased density. The presence of contrast does not exclude hemorrhage, as the two can coexist. Measuring the attenuation of the involved regions may be helpful, as contrast enhancement will usually demonstrate higher values (as high as 160 HU) than blood. Follow-up CT is also useful, as the contrast enhancement typically resolves completely within 24 h. In patients undergoing attempted endovascular revascularization for acute infarct, a hyperdense lesion with maximum HU > 90 that persists after 24 h is considered contrast extravasation and is highly associated with hematoma formation. On the other hand, the common finding of parenchymal, subarachnoid, and intraventricular hyperattenuation due to contrast accumulation following uneventful embolization of cerebral aneurysms is almost always clinically insignificant. In unclear cases parenchymal contrast stain may also be differentiated from hemorrhage by performing brain MRI. Dual-energy CT with 80 and 140 KV seems to reliably distinguish intracranial hemorrhage from iodinated contrast. In acute ischemic patients treated with intra-arterial thrombolysis, sulcal hyperintensity may be found on FLAIR images, which is likely caused by iodinated contrast medium.