Effects of craniectomy on cerebrospinal fluid pressure gradient in the craniospinal space in different body positions of cats.

Abstract

Aim: To assess whether a cranial defect in anesthetized cats alters cerebrospinal fluid (CSF) pressure distribution across the craniospinal axis in different body positions in the setting of intracranial normotension.

Methods: After standardized parietal craniectomy, intracranial and lumbar CSF pressures were simultaneously measured in eight adult anesthetized (?-chloralose, i.p. 100 mg/kg) cats in different body positions: horizontal (0°), head-up (45°; 90°), and head-down (225°; 270°). CSF pressure gradient represents the difference between CSF pressure values in the lateral ventricle (LV) and lumbar subarachnoid space (LSS) in each body position.

Results: At 0°, CSF pressures in the LV and LSS were similar (16.2±0.9 vs 15.8±1.2 cm H2O, respectively). In the 90° head-up position, LV pressure was subatmospheric (?1.5±0.5 cm H2O), while LSS pressure simultaneously increased (31.4±1.0 cm H2O). Conversely, in the head-down 270° position, LSS pressure was negative (?1.7±1.5 cm H2O) and LV pressure increased (30.0?±?1.8 cm H2O). Difference between LV and LSS pressures is strongly correlated with hydrostatic difference between the two recording points in the head-up and the head-down position. LV pressure at 90° in the craniectomy group was significantly higher than previously published in cats with an intact cranium in the same position (P<0.001).

Conclusion: Hydrostatic CSF pressure gradient across the craniospinal axis remained unaltered by craniectomy. The finding that craniectomy in the head-up position of animals without intracranial pathology resulted in an intracranial pressure increase may offer additional explanation for the trephined syndrome pathophysiology.