Prospective neuropsychological investigation of patients with supratentorial arteriovenous malformations.

Thirty-one patients subjected to direct radical excision of a supratentorial arteriovenous malformation (AVM) participated in a comprehensive neuropsychological assessment both pre-operatively and at 4 and 12 months after surgery. The sample constitutes a consecutive series of patients who could complete the neuropsychological assessment before surgery. At the pre-operative assessment the mean results of all the tests fell very close to the average performance of age-equivalent normative samples. Postoperatively, the mean results showed a mild to moderate deterioration of performance on most cognitive and perceptual tasks by 4 months after surgery and a return approximately to the premorbid level by 12 months. Twelve of 15 patients with pre-operative epileptic seizures remained seizure free on medication during this first postoperative year, while two developed seizures de novo. Headache was cured or markedly reduced in all 16 patients incapacitated by headache prior to surgery. No definite emotional or affective changes after surgery were reported by the patients or their relatives. Comparison of pre-operative test results of patients with right-sided and left-sided AVM showed significant differences on five of 24 test parameters. Postoperatively, the number of statistically significant differences increased to nine test parameters at 4 months and ten at the 12-month assessment. The increase in number of statistically significant differences appears to reflect a moderate focal impact of the surgical intervention on cognitive functions in six of the 31 patients (19%). Postoperative improvement of test performance exceeding what may be ascribed to practice effects and chance fluctuations was only encountered in one patient. The present results therefore lend little empirical support to the so-called 'cerebral steal' hypothesis.