Changes in parenchymal and ventricular pressure with experimental epidural compression

A rabbit model was used to study the changes in intracranial pressure and parenchymal morphology that accompany epidural compression. A catheter in the left lateral ventricle and an intraparenchymal moist wick in each cerebral hemisphere were used to monitor intracranial pressures. With the balloon uninflated, the pressures in 12 rabbits were similar: 67.8 +/- 34.9 mmH2O for the left lateral ventricle, 61.7 +/- 31.0 mmH2O for the right parenchymal wick, and 58.3 +/- 29.1 mmH2O for the left parenchymal wick (mean +/- S.D.). With inflation of a right parietal epidural balloon to 0.4 cm3, the left ventricular pressure rose significantly to 168 +/- 57.5 mmH2O (p less than 0.001, Student's t-test) and the right hemisphere parenchymal pressure to 114.3 +/- 52.1 mmH2O (p less than 0.001). The left frontal parenchymal pressure increased, but not significantly. There was no evidence of blood-brain barrier breakdown by the Evans blue dye technique 2 hours after compression. Similarly, there was no infarction as gauged by 235triphenyl-2M-tetrazolium chloride infusion at 2 weeks. These data demonstrate that significant pressure asymmetries between hemispheres occur with epidural compression. In the rabbit, a 0.4-cm3 mass is not enough to cause blood-brain barrier breakdown or tissue necrosis. In the first 2 hours of compression th ventricular pressure is higher than the parenchymal pressure, perhaps because of obstruction of cerebrospinal fluid flow around the convexities.