Conventional Brain MRI in Carbon Monoxide Poisoning

Carbon monoxide poisoning is a common fatal condition which can have acute or chronic presentation with varying severity. It commonly involves globus pallidus and putamen but can involve other parts of brain. Conventional MRI using T1 weighted,T2 weighted and FLAIR sequences are helpful in determining the extent of damage to the brain. However, appropriate clinical and laboratory findings should supplement findings on imaging.


INTRODUCTION
Carbon monoxide poisoning (CO) is a common, inadvertent, and potentially fatal condition.It causes serious damage to brain the extent of which is directly related to the prognosis. 1Patients may present acutely or continue to be symptomatic for years with different neuropsychiatric manifestations.MRI helps to assess objective damage to the brain.We present a similar case with findings on conventional MRI.

CASE REPORT
A 24 year old male with no past illness was found unconscious in the bathroom for unknown duration.The patient had taken hot water shower run by gas geyser.He was brought to the emergency department with the Glasgow Coma Scale of 3/15.Emergency resuscitation was carried out.Vitals with oxygen saturation on pulse oxymetry and neurological examination were normal.
Initial blood gas analysis revealed respiratory acidosis with pO2 level of 39 mmHg.Complete hemogram and electrocardiogram were normal.An emergent CT of the brain was reported as normal (

DISCUSSION
Carbon monoxide is a colourless, odourless toxic gas produced during incomplete combustion of carboncontaining compounds.CO inhalation is the most common cause of fatal poisoning worldwide. 2CO inhibits electron transport which results in disruption of mitochondrial cellular respiratory enzymes.Symptoms of poisoning are non-specific and vary from mild constitutional upset to coma, myocardial ischaemia and death.
Magnetic resonance imaging (MRI) can reveal abnormal findings in CO-poisoned patients and is more sensitive than CT for their detection. 3Carbon monoxide in particular has a propensity to affect the globus pallidus which is vulnerable to generalized disease process due to rich vascular supply and high metabolic activity.In acute CO poisoning, CT of the brain usually demonstrates bilateral symmetrical hypoattenuation of the globi pallidi as a result of underlying necrosis. 5is seen on MR imaging as areas of increased signal on T2-weighted, fluid attenuated inversion recovery (FLAIR) and DW sequences as seen in our case.Contrastenhanced T1-weighted images may also demonstrate patchy or peripheral enhancement of the necrotic globus pallidus in cases of acute poisoning.Structures such as the caudate nucleus, putamen, thalamus, brainstem and cerebellum may also be involved in acute CO poisoning demonstrating increased signal on T2-weighted and FLAIR images with an asymmetrical distribution.Involvement of these structures may also be delayed, manifesting up to five days after the acute episode of poisoning.Cerebellar and brainstem signal abnormalities are a manifestation of more severe poisoning, as the posterior structures have a higher threshold for hypoxic injury. 6,7Diffusion MR imaging is more sensitive to the damage during the early stage of carbon monoxide poisoning. 8Diffuse hypoxic-ischaemic encephalopathy usually develops only in cases of acute and severe CO poisoning or prolonged exposure.This usually presents as diffuse increased signal in the cortex on T2-weighted or FLAIR images.Focal cortical injury is considerably less common, usually affecting the temporal lobe or hippocampus. 5ffuse brain atrophy and cerebral white matter demyelination are late manifestations of CO poisoning. 9,10he most common sites of involvement are the periventricular white matter and centrum semiovale; the subcortical white matter, corpus callosum and both the internal and external capsules are involved in cases of severe poisoning. 11obus pallidus lesions in many cases do not correlate directly to clinical status and outcome; however, the presence of diffuse white matter disease is a more reliable index of both. 3 conclusion, correlation of typical imaging features with clinical history and laboratory data is of utmost importance in arriving at the correct diagnosis.Conventional MRI still proves to be an invaluable asset in quantifying the damage to the CO poisoned brain although early changes may be well discerned with newer techniques.
Fig 1.1).A provisional diagnosis of encephalopathy secondary to Carbon Monoxide poisoning was made and he was transferred to the intensive care unit and maintained on 100% oxygen.He recovered and was extubated after 13 hours.MRI performed 15 hr post admission revealed symmetrical decreased signal intensity in bilateral lentiform nuclei in T1 weighted images (Fig 1.2) with increased signal intensity in T2 weighted images (Fig 1.3, 1.4) and FLAIR images (Fig 1.5).