Lateral ventricle size on CT film and lumbar pressure change due to CSF drainage were measured in 15 patients with hydrocephalus to determine indications for shunt operation. Changes of ventricular size were classified into the following two patterns: Pattern A showing decrease in size; and Pattern B showing no change. The degree of decrease in Pattern A was 9.9%, 14.2%, and 16.3% in accordance with CSF drainages of 10, 15, and 20 ml, respectively. Lumbar pressure changes were also classified

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... to the following two patterns: Pattern C showing rapid decrease to an extent of 22% of the initial pressure after 5-10 ml of CSF drainage; and Pattern D also showing rapid decrease up to a pressure ranging between 100-150 mmH20, and continuous slow decrease with drainage thereafter. Ventriculo-peritoneal and lumbar subarachnoid peritoneal shunt were effective in cases with Pattern A and D combination, but shunt operation was noneffective for Pattern B and C combination cases. In cases of Pattern B and D combination, shunt operation seemed unnecessary.