A sereis of 89 patients diagnosed between 1988 and 1993 with computerized tomography (CT) as having subdural hematoma was studied retrospectively in order to evaluate the age of the subdural hematomas according to its appearance on CT scans. In
all
the
patients, the interval from onset of injury to performance of CT scans was more than 2 days. The patients were divided into 4 groups based on the difference in density of the hematoma as seen on the CT scans ; hyperdensity (16.9%), isodensity
(30.3%),
hypodensity (19.1%). and mixed-density (33.7%) groups. The mean interval from onset of injury to diagnosis in hyperdensity, hypodensity, mixed density and isodensity groups was 15.7±18.3 days, 18.8±27.9 days, 35.6±62.1 days, and 47.6±52.1
days,
respectively. The configuration of the hematomas on CT scans was crescentic in 74.2%, planoconvex in 12.4%, and biconvex in 13.5%. As the interval became longer. the hematomas tended to take on a planoconvex or biconvex shape rather than the
crescentic
shape ; when the interval from onset of injury to diagnosis was within 7 days. crescentic shape was observed in 91%, within 8 to 21 days. 69%, and over 21 days. 58%.
It is concluded from these findings that subdural hematomas undergo a progressive change in their attenuation as the hematomas age, changing from the initial hyperdense stage, go through a hypodense stage, and eventually to an isodense stage.
These
changes of attenuation values correlates fairly well with the rebleeding theory. The appearance of the hematomas as seen on CT scans also tended to change from the initial crescentic shape to the planoconvex or biconvex shape with time. Howerer,
given
the possible variations of attenuation values and shapes of subdural homatomas, assumption of the age of the hematomas based on CT findings alone should be made with caution.
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