A positron emission tomography study of cerebrovascular reserve before and after shunt surgery in patients with idiopathic chronic hydrocephalus

Object. In this study the authors use positron emission tomography (PET) to investigate cerebral blood flow (CBF) and cerebrovascular reserve (CVR) in chronic hydrocephalus. Methods. Ten patients whose mean age was 67 +/- 10 years (mean +/- standard deviation [SD]) were compared with 10 healthy volunteers who were 25 +/- 3 years of age. Global CBF and CVR were determined using O-15-H2O and PET prior to shunt placement and 7 days and 7 months thereafter. The CVR was measured using 1 g acetazolamide. Neurological status was assessed based on a score assigned according to the methods of Stein and Langfitt. Seven months after shunt placement, five patients showed clinical improvement (Group A) and five did not (Group B). The average global CBF before shunt deployment was significantly reduced in comparison with the control group (40 +/- 8 compared with 61 +/- 7 ml/100 ml/minute; mean +/- SD, p < 0.01). In Group A the CBF values were significantly lower than in Group B (36 +/- 7 compared with 44 +/- 8 ml/100 ml/minute; p < 0.05). The CVR before surgery, however, was not significantly different between groups (Group A = 43 +/- 21%, Group B = 37 +/- 29%). After shunt placement, there was an increase in the CVR in Group A to 52 +/- 37% after 7 days and to 68 +/- 47% after 7 months (p < 0.05), whereas in Group B the CVR decreased to 14 +/- 18% (p < 0.05) after 7 days and returned to the preoperative level (39 +/- 6%) 7 months after shunt placement. Conclusions. The preliminary results indicate that a reduced baseline CBF before surgery does not indicate a poor prognosis. Baseline CBF before shunt placement and preoperative CVR are not predictive of clinical outcome. A decrease in the CVR early after shunt placement, however, is related to poor late clinical outcome, whereas early improvement in the CVR after shunt placement indicates a good prognosis.