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

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.