Cerebral blood flows and tissue oxygen levels associated with maintenance of the somatosensory evoked potential and cortical neuronal activity in focal ischemia.

The middle cerebral artery was occluded in 18 cats to evaluate the physiological consequences of cerebral blood flow reductions on the somatosensory evoked potential, spontaneous neuronal activity, and oxygen availability in the ipsilateral and contralateral hemispheres. In the ipsilateral ectosylvian gyrus high-grade ischemia was produced as blood flow in the gray matter was reduced from 52.1 +/- 8.6 (mean +/- SE) to 13.3 +/- 9.0 ml/100 g/min and in the white matter from 33.8 +/- 5.6 to 6.1 +/- 6.4 ml/100 g/min. This significant reduction (p less than 0.05) was associated with abolition of the cortical component of the somatosensory evoked potentials. In all animals occlusion resulted in a predictable extended latency change and a variable amplitude response of the cortical component of the contralaterally recorded somatosensory evoked potentials. In 5 animals, oxygen availability was measured and spontaneous neuronal activity in the contralateral hemisphere was recorded. Volume expansion and hemodilution with either dextran or saline infusions elevated cerebral blood flow in the contralateral gray matter significantly (p less than 0.05) compared with the control and clip values. Ipsilateral spontaneous activity stopped within 4-12 minutes of occlusion, while contralateral spike activity persisted at rates at least equal to those recorded immediately following occlusion.

Comparison of the somatosensory evoked potential and the direct cortical response following severe incomplete global ischemia: selective vulnerability of the white matter conduction pathways.

Eight cats were subjected to graded hemorrhagic hypotension following bilateral carotid ligation to produce incomplete global cerebral ischemia. Three additional cats served as controls. The somatosensory evoked potential (SEP) and direct cortical response (DCR) were monitored in all animals and in each case, the cortical component of the SEP was abolished during progressive ischemia while the morphology of the DCR was well-preserved but with reduced amplitude. Determinations of adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in cerebral cortex and white matter were made in five experimental cats and the three controls. At the time of failure of the cortical SEP, PCr was dramatically reduced and lactate moderately elevated in the white matter while ATP remained unchanged. Cortical lactate was only mildly elevated and PCr and ATP were unchanged accounting for preservation of the DCR. In this model of global ischemia, abolition of the cortical SEP is due to a block of stimulus conduction in white matter projection pathways. A hypothesis to explain the observed metabolic changes is presented and correlation is made to clinical situations.

MR identification of bleeding site in subarachnoid hemorrhage with multiple intracranial aneurysms.

We report a case of multiple aneurysms with subarachnoid hemorrhage in which CT was inconclusive as to the source of bleeding and in which the angiographic criteria were misleading. Magnetic resonance demonstrated a focal subarachnoid hematoma adjacent to the ruptured aneurysm.

Failure of the somatosensory evoked potential following middle cerebral artery occlusion and high-grade ischemia in the cat--effects of hemodilution.

Acute focal ischemia was created in 10 cats by unilateral retro-orbital middle cerebral artery (MCA) occlusion. Regional cerebral blood flow (CBF) was determined utilizing the hydrogen clearance technique from electrode recordings within the gray matter and white matter of the ectosylvian gyrus of both hemispheres. The somatosensory evoked potential (SSEP) was obtained during contralateral median nerve stimulation. When the MCA was clipped the white and gray matter blood flows in the ipsilateral ectosylvian gyrus were reduced to 14.8 +/- 19.6% and 19.3 +/- 23.7% of control, and the cortical component of the SSEP was abolished. In the contralateral hemisphere an average increase of 3.5% above the control latency and a 10% mean depression in the amplitude of the cortical component of the SSEP were observed following occlusion. CBF in the contralateral hemisphere was unaffected by the MCA clip. Infusion of saline or dextran to lower the hematocrit by approximately 45% did not significantly improve blood flow or restore the SSEP in the hemisphere ipsilateral to the MCA clip. However, significant increases in the contralateral hemisphere gray matter CBF occurred following hemodilution while the latency of the cortical component of the SSEP in this same hemisphere was significantly extended. Elevations in gray and white matter blood flows were achieved in the experimental hemisphere of 3 of 10 cats suggesting a wide range of variation in the collateral circulation.

Familial pineoblastoma. Report of two cases.

Two cases of pineoblastoma are presented. One occurred in a 12-year-old girl and the other, 20 months later, in her 43-year-old mother. A possible genetic basis and mutual exposure to an environmental factor responsible for the expression of a tumor gene are postulated in the discussion.

Alteration of somatosensory evoked potentials in response to global ischemia.

The somatosensory evoked potential (SEP) measured in response to median nerve stimulation was correlated with cortical and white matter cerebral blood flow (CBF), adenosine triphosphate (ATP), and lactate levels in 14 cats subjected to graded hemorrhagic hypotension following bilateral carotid artery ligation. Three additional cats served as controls. Regional CBF was determined by the hydrogen clearance method, and the time for conduction of the sensory stimulus from the thalamus to the cortex (the thalamocortical conduction time), was used to assess SEP latency changes. A reproducible sequence of changes occurred in the SEP as ischemia developed. There was an early conduction delay that correlated well with mild white matter ischemia. Amplitude reductions in the SEP began as significant cortical ischemia occurred. The cortical SEP was abolished when white matter CBF and ATP fell to critical levels.