15
Intracranial Hemorrhages

Intracranial hemorrhages are commonly encountered; they can have a variety of causes with differing appearances on imaging depending on the age of the hematoma. They are generally classified into five distinct stages: hyperacute (<12 hours), acute (12 hours to 2 to 3 days), early subacute (2 or 3 to 7 days), late subacute (8 days to 1 month), and chronic (>1 month to years). Characteristic imaging appearances have been described on magnetic resonance imaging (MRI) for blood in intraparenchymal hematomas at these different stages based on the presence of blood products, their oxygenation states, and breakdown products. However, these descriptions have recently been shown to only partly correspond to the actual appearance of hematomas. The characteristic intraparenchymal hematoma appearance has been detailed elsewhere, but will be summarized here for easy reference (Table 15.1). Computed tomography (CT) is often the modality initially used when a patient presents with acute hemorrhage.

Abbreviations: Hypo, hypointense; hyper, hyperintense; iso, isointense; MRI, magnetic resonance imaging; T1WI, T1-weighted MRI; T2WI, T2-weighted MRI.

The hematoma appearance can vary based on its age and various characteristics including hematocrit level and anticoagulation status of the patient. Hyperacute blood can appear iso-dense to brain, but soon becomes hyperdense, and then decreases in density in the late subacute and chronic stages passing through a stage where it is isodense to brain. Ultimately, a small low-density cavity may remain. Anemia and anticoagulation can result in the acute hematoma being intermediate in density, but active bleeding must also be considered if hypodense areas are seen.

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