[Ventricular dilation during the treatment of subdural hygromas]

Fifty-one cases with subdural hygroma experienced in the past 20 years were retrospectively reviewed. Eight patients showed definite ventricular dilation differing from simple restoration of the ventricles following disappearance of the cavity. The mean age was 72.4 years. Six patients presented with mental change as the initial symptom. On the initial computed tomography (CT), 75% of the cases had bilateral lesions, all were low density, and 88% were crescent shaped. Trepanation performed on six patients yielded watery clear or xanthochromic fluid. Nine to 61 days (mean 4 weeks) after admission, definite ventricular dilation was observed. Cisternography performed in four patients was all abnormal, although cerebrospinal fluid (CSF) pressure was within normal range. Cerebral blood flow images using 123I-iodoamphetamine and single photon emission CT in four patients revealed periventricular low uptake which was disproportionately large compared with the ventricular span on CT. A ventriculoperitoneal shunt was placed in four patients. The final outcome, however, was poor irrespective of treatment. These findings indicate that an impairment of the CSF circulation was not the sole cause of the ventricular dilation. Low CSF pressure and the disproportionately large periventricular low perfusion, compared with the ventricular span on CT scan, suggest a pre-existing periventricular parenchymal damage, which had been subsequently compromised by the presence of subdural mass lesion. Therefore, attention should be paid in aged patients with bilateral low dense, crescent-shaped subdural hygroma, presenting with mental change, for the risk of subsequent ventricular dilation which may affect the functional outcome.