Measurement of local directional pressures in the brain with mass

In order to understand the effects and the direction of pressure transmitted from a mass lesion through various brain structures, miniature strain gauges were inserted in different brain locations in eight anesthetized monkeys. Mass lesions were created by inflating a balloon in either of two locations--subcortical in four animals (Group I) and deep (lateral to the caudate nucleus) in the other four animals (Group II). Anterior-posterior directed pressures were thus measured from a gauge placed in the parietal lobe, and lateromedially directed pressures (LM-dPs) were measured from gauges in the temporal lobe and midbrain. Intracranial pressure, systemic mean arterial pressure, and cerebral blood flow were also monitored. After balloon inflation was begun, temporal changes in pressure were recorded from gauges as percentage increase or decrease from baseline measurements. In both groups, balloon inflation caused a gradual increase in the parietal lobe anterior-posterior directed pressure with a concomitant increase in intracranial pressure and a decrease in cerebral blood flow. The temporal lobe gauge in Group I recorded an initial negative followed by a positive LM-dP with further balloon inflation. In Group II, this gauge recorded a positive LM-dP throughout. The midbrain gauges in both groups recorded an initial positive followed by a negative LM-dP. This reversal in the direction of pressure in the midbrain occurred just before the supratentorial pressure reached a peak and was noted to be concurrent with a sudden rise in mean arterial pressure and a decline in cerebral blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)