[Chronic subdural hematoma: diagnostic imaging studies].

CT-scan is able to provide the diagnosis of chronic subdural hematoma in more than 90% of the cases. It usually shows a peri-cerebral fluid collection along the convexity, with a convex outer border, and an irregular concave inner border. The density of the collection depends on the age of the hematoma. The main difficulties, in term of diagnosis, result from bilateral isodense chronic subdural hematoma, and differential diagnosis between hematoma, hygroma, and empyema. Some rare localisations can sometimes be seen (posterior fossa, skull base...). A double density with a sedimentation level, or heterogeneity of the hematoma, can sometimes be seen too. Chronic subdural hematoma is demonstrated by MRI in almost 100% of the cases. The intensity of the collection, in T1 and T2 sequences, depends on the age of the hematoma.