Magnetic resonance imaging of the rat brain following acute carbon monoxide poisoning

The Value of Morphological Neuroimaging after Acute Exposure to Toxic Substances

Many toxic agents induce brain dysfunction and/or lesions. Modern neuroimaging techniques, such as CT and more recently magnetic resonance imaging (MRI), are able to demonstrate toxic brain lesions at both early and delayed phases of disease progression. In the early phase, neuroimaging enables the detection of acutely injured brain areas responsible for sudden onset of neurological dysfunction, but the severity and the extension of brain lesions on neuroimages do not necessarily parallel the severity of the clinical status. In the chronic phase, when neurological dysfunction has become permanent, neuroimaging allows precise identification of neuroanatomical sequelae that do not necessarily match the severity of the chronic neurological impairment. Papers in the medical imaging literature have dealt mainly with the brain changes induced by 'chronic exposure' to toxic substances such as solvents or heavy metals. This article selectively reviews the main radiological changes observed on CT/magnetic resonance (MR) neuroimages after 'acute exposure' to industrial products (methanol [methyl alcohol], ethylene glycol), environmental agents (cyanide, carbon monoxide), pharmaceuticals (insulin, valproic acid) and illicit substances (heroin, cocaine). Different kinds of lesions, which lack specificity for toxic injury, can be observed on radiological images, but deep grey matter lesions with symmetrical distribution throughout basal ganglia are most often seen. However, such findings have also been reported after anoxic-ischaemic insults or during severe metabolic disturbances. Lesions in the white matter may also be present in the case of acute exposure to toxic agents. The true prognostic value of toxic-induced brain changes in the acute phase in CT or MR studies is unclear, although serial MRI may add new information as may quantitative or molecular imaging techniques such as the MR diffusion-weighted imaging or MR spectroscopy.

The magnetic resonance imaging appearances of the brain in acute carbon monoxide poisoning

AIMS

To describe the magnetic resonance imaging (MRI) appearances of the brain in acute carbon monoxide poisoning, the commonest cause of accidental poisoning in Europe and the U.S.A. To attempt to correlate the imaging findings with patient outcome as an aid to prognosis.

MATERIALS AND METHODS

Brain MRI was performed on 19 consecutive patients, who had sustained acute carbon monoxide poisoning, as soon as possible after their referral to the regional Hyperbaric Unit at the Royal Hospital, Haslar. All patients were unconscious on arrival, and had received at least one treatment with hyperbaric oxygen by the time of first MR. The imaging findings were analysed independently by two experienced MR radiologists, with a third radiologist arbitrating on discrepant results.

RESULTS

Thirteen male and six female patients, age range 21-70 years (mean 38.7 years) underwent MR an average of 35.6 h (range 6-126 h) following presentation at the referring centre. MR (at 0.5T) revealed abnormalities in the following areas: globus pallidus (n = 12); other basal ganglia [ n = 5: entire lentiform (globus pallidus and putamen), putamen alone, caudate nucleus, thalamus]; white matter (n = 6: periventricular, subcortical, other); cerebral cortex (n = 5), either localized or general; medial temporal lobe in the region of the hippocampus (n = 4). The majority of the patients with hyperintensity in the region of the hippocampus (n = 3) had no other area of cortical involvement. Two patients showed abnormalities in the cerebellum. Normal appearances were seen on the initial MR in seven patients.

CONCLUSION

The appearances of the brain following acute CO poisoning are varied, and have previously been the subject of case reports or small studies, most of which have have addressed the delayed sequelae of this condition. This study, the first large series undertaken in the acute phase, confirms that, although the globus pallidus is the commonest site of abnormality in the brain, the effects of CO poisoning are widespread. The extent of damage correlates with clinical outcome, and therefore aids management and prognosis.

Effects of hypo- and hyperglycemia on brain energy metabolites in mice exposed to carbon monoxide

Hypoglycemia and hyperglycemia were induced in mice by fasting and by injecting with glucose, respectively. These and normally fed (normoglycemic) animals were exposed to 0.5% carbon monoxide (CO) for 10 min. This altered concentrations of energy metabolites in the brain, including decreases in phosphocreatine (PCr) and increases in creatine and lactate. The only difference between normoglycemic and hypoglycemic mice was lower lactate in the latter. In hyperglycemic mice, PCr and ATP were better preserved during CO exposure and lactate was lower than in normoglycemic mice. Blood glucose concentrations correlated well with glucose but not with lactate in the brain. Thus, moderate hypo- or hyperglycemia seems not to exacerbate CO-induced alterations of brain energy metabolism.