Dynamics of cerebral blood flow and metabolism in patients with cranioplasty as evaluated by Xe-133 CT and P-31 magnetic resonance spectroscopy

Objective-Prolonged improvement in neurological and mental disorders has been seen after only cranioplasty in patients initially treated with external decompression for high intracranial pressure. The objective was to evaluate, using Xe-133 CT and P-31 magnetic resonance spectroscopy (MRS), how restoring the bone itself can influence cerebral blood flow and cerebral energy metabolism after high intracranial pressure is attenuated. Methods-Seven patients (45-65 years old) who had undergone external decompression to prevent uncontrollable intracranial hypertension after acute subarachnoid haemorrhage were evaluated. Cerebral blood flow and metabolic changes were evaluated before and after cranioplasty. Results-The ratio of phosphocreatine to inorganic phosphate (PCr/Pi), which is a sensitive index of cerebral energy depletion, was calculated and beta-ATP was measured. The cerebral blood flow value in the thalamus was normalised, from 44 (SD 9) to 56 (SD 8) ml/100 g/min (P < 0.01) and the value in the hemisphere increased from 26 (SD 3) to 29 (SD 4) ml/100 g/min on the side with the bone defect. The PCr/Pi ratio improved greatly from 2.53 (SD 0.45) to 3.01 (SD 0.24) (P < 0.01). On the normal side, the values of cerebral blood flow and PCr/Pi increased significantly (P < 0.01) after cranioplasty, possibly due to transneural suppression. The pH of brain tissue was unchanged bilaterally after cranioplasty. Conclusion-Cranioplasty should be carried out as soon as oedema has disappeared, because a bone defect itself may decrease cerebral blood flow and disturb energy metabolism.