Computed tomography and magnetic resonance imaging in the evaluation of chronic subdural hematomas

Twenty-two patients with chronic subdural hematomas (C.S.D.H.) and subdural effusion were evaluated by means of computed tomography (CT) and magnetic resonance imaging (MRI). Surgical treatments were given to seventeen of those patients. Three of them showed an isodense collection on CT; however, it was clearly demonstrated by MRI. In three patients, small C.S.D.H. which could not be detected by CT were identified by MRI. In patients with CT numbers of over thirty, all the operative cases were hematomas, where in those with CT numbers under twenty, all cases were those of effusion. Hematomas and effusion co-existed in the patients with CT numbers between twenty and thirty. A comparison of the CT numbers and the T1 values revealed that there was a tendency for higher CT numbers and shorter T1 values, to go together, as did lower CT numbers and longer T1 values. However, in CT numbers between twenty and forty there was a large variation in the T1 values. Most of the C.S.D.H. were demonstrated as a zone of shortened T1 values (T1 < 700 msec), while most of the cases of effusion were demonstrated as longer T1 values (T1 > 1000 msec). However, a few hematoma cases revealed longer T1 values (T1 > 1000 msec). In the SE image, all the hematoma cases (six lesions in five cases) were shown as signal regions higher than those of the cerebrospinal fluid (C.S.F.), while all the effusional cases (three lesions in two cases) were shown as iso-signal regions similar to those of C.S.F. The authors suggest that MRI may be the best method to identify the C.S.D.H. and to distinguish between hematoma and effusion when used in connection with the CT and MRI. (author)