Evaluation of periventricular radiolucency in hydrocephalus by dynamic CT studies

The association of periventricular radiolucency (PVL) in normal pressure hydrocephalus (NPH) on CT scan is a common finding. However, it is difficult to differentiate NPH from atrophy or infarctions in which shunt surgery does not reverse these conditions. To distinguish NPH from these, we examined PVL by means of dynamic CT (DCT) studies. We investigated 12 elderly patients presenting with gait disturbance, urinary incontinence and mental dysfunction who had both enlarged lateral ventricles and PVL. All patients had laboratory investigations, including radioisotope and CT cisternography and Xenon CBF studies. Nine patients were shunted because of abnormal CSF dynamics. Varying degrees of clinical improvement after surgery were observed in 6 cases. A difference of arrival time (AT) between PVL and thalamus obtained from time-density-curve was calculated in each patient. The AT difference was 6.2±1.5 sec. in the shunt-effective group, and 1.4±1.3 sec. in both, the shunt in effective and ineligible group, this was highly significant (p<0.01). We also measured peak time (PT) in PVL, of the thalamus and anterior cerebral artery, but no significant correlation was obtained. An AT difference between PVL and thalamus obtained from DCT studies is a clinically useful diagnostic tool for the evaluation of NPH. (author)