[Imaging in acute toxic encephalopathy]

Neuroimaging of acute and chronic unilateral and bilateral thalamic lesions

The thalami are bilateral ovoid grey matter cerebral structures bordering the third ventricle on both sides, which participate in functions such as relaying of sensory and motor signals, regulation of consciousness, and alertness. Pathologies affecting the thalami can be of neoplastic, infectious, vascular, toxic, metabolic, or congenital origin.The purpose of this review is to provide a comprehensive approach to the thalamus focusing on its anatomy, the main pathologies affecting this structure and their radiological semiology on CT and MRI. We will also illustrate the importance of multimodal MR imaging (morphologic sequences, diffusion-weighted imaging, perfusion, spectroscopy) for the diagnosis and treatment of these conditions.

[Metabolic encephalopathies]

Metabolic encephalopathies (ME) are a common cause of admission to emergency rooms, to hospitalization wards or to intensive care units. They could account for 10 to 20% of causes of comatose states in ICU and could be associated to a poor outcome especially in older patients. Nevertheless, they are often reversible and are associated with a favorable outcome when diagnosed and rapidly treated. They correspond to an altered brain functioning secondary to the deficiency of a substance that is mandatory for the normal brain functioning or to the accumulation of a substance that can be either endogenous or exogenous. It preferably occurs in co-morbid patients, complicating its diagnosis and its management. Altered brain functioning, going from mild neuropsychological impairment to coma, movement disorders especially myoclonus and the absence of any obvious differential diagnosis are highly suggestive of the diagnosis. Whereas some biological samplings and brain MRI are essential to rule out differential diagnosis, some others, such as electroencephalogram, may be able to propose important clues in favor of the diagnosis. Once simple symptomatic measures are introduced, the treatment consists mainly in the correction of the cause. Specific treatment options are only seldom available for ME; this is the case for hepatic encephalopathy and some drug-induced encephalopathies. We will successively describe in this review the main pathophysiological mechanisms, the main causes, favoring circumstances of ME, the differential diagnosis to rule out and the etiological work-up for the diagnosis. Finally, a diagnostic and therapeutic strategy for the care of patients with ME will be proposed.

A rare case of toxic optic neuropathy secondary to consumption of neem oil

A 35-year-old female was referred to our hospital with bilateral loss of vision of two days duration. She gave history of consumption of about 150 ml of neem oil five days back. Examination revealed no perception of light in both eyes. Both pupils were dilated and sluggishly reacting to light. Her fundus examination showed bilateral hyperemic, edematous discs and also edema extending along the superior and inferior temporal vascular arcade. Magnetic resonance imaging (MRI) scan showed bilateral putaminal regions with altered signal, hypointensities in T1-weighted images, hyperintensities on T2-weighted, images and hyperintense on Fluid Attenuation Inversion Recovery (FLAIR) images suggestive of cytotoxic edema due to tissue hypoxia. Her vision improved to 20/200 in both eyes with treatment after two months. This is the first case report of such nature in the literature to the best of our knowledge.

Does health information exchange reduce unnecessary neuroimaging and improve quality of headache care in the emergency department?

BACKGROUND

Health information exchange (HIE) is advocated as an approach to reduce unnecessary testing and improve quality of emergency department (ED) care, but little evidence supports its use. Headache is a specific condition for which HIE has theoretical benefits.

OBJECTIVE

To determine whether health information exchange (HIE) reduces potentially unnecessary neuroimaging, increases adherence with evidence-based guidelines, and decreases costs in the emergency department (ED) evaluation of headache.

DESIGN

Longitudinal data analysis

SUBJECTS

All repeat patient-visits (N = 2,102) by all 1,252 adults presenting with headache to a Memphis metropolitan area ED two or more times between August 1, 2007 and July 31, 2009.

INTERVENTION

Use of a regional HIE connecting the 15 major adult hospitals and two regional clinic systems by authorized ED personnel to access the patient's record during the time period in which the patient was being seen in the ED.

MAIN MEASURES

Diagnostic neuroimaging (CT, CT angiography, MRI or MRI angiography), evidence-based guideline adherence, and total patient-visit estimated cost.

KEY RESULTS

HIE data were accessed for 21.8 % of ED patient-visits for headache. 69.8 % received neuroimaging. HIE was associated with decreased odds of diagnostic neuroimaging (odds ratio [OR] 0.38, confidence interval [CI] 0.29-0.50) and increased adherence with evidence-based guidelines (OR 1.33, CI 1.02-1.73). Administrative/nursing staff HIE use (OR 0.24, CI 0.17-0.34) was also associated with decreased neuroimaging after adjustment for confounding factors. Overall HIE use was not associated with significant changes in costs.

CONCLUSIONS

HIE is associated with decreased diagnostic imaging and increased evidence-based guideline adherence in the emergency evaluation of headache, but was not associated with improvements in overall costs. Controlled trials are needed to test whether specific HIE enhancements to increase HIE use can further reduce potentially unnecessary diagnostic imaging and improve adherence with guidelines while decreasing costs of care.

Toxic encephalopathy

This article schematically reviews the clinical features, diagnostic approaches to, and toxicological implications of toxic encephalopathy. The review will focus on the most significant occupational causes of toxic encephalopathy. Chronic toxic encephalopathy, cerebellar syndrome, parkinsonism, and vascular encephalopathy are commonly encountered clinical syndromes of toxic encephalopathy. Few neurotoxins cause patients to present with pathognomonic neurological syndromes. The symptoms and signs of toxic encephalopathy may be mimicked by many psychiatric, metabolic, inflammatory, neoplastic, and degenerative diseases of the nervous system. Thus, the importance of good history-taking that considers exposure and a comprehensive neurological examination cannot be overemphasized in the diagnosis of toxic encephalopathy. Neuropsychological testing and neuroimaging typically play ancillary roles. The recognition of toxic encephalopathy is important because the correct diagnosis of occupational disease can prevent others (e.g., workers at the same worksite) from further harm by reducing their exposure to the toxin, and also often provides some indication of prognosis. Physicians must therefore be aware of the typical signs and symptoms of toxic encephalopathy, and close collaborations between neurologists and occupational physicians are needed to determine whether neurological disorders are related to occupational neurotoxin exposure.

The corpus callosum: white matter or terra incognita

The corpus callosum is the largest white matter structure in the brain, consisting of 200-250 million contralateral axonal projections and the major commissural pathway connecting the hemispheres of the human brain. The pathology of the corpus callosum includes a wide variety of entities that arise from different causes such as congenital, inflammatory, tumoural, degenerative, infectious, metabolic, traumatic, vascular and toxic agents. The corpus callosum, or a specific part of it, can be affected selectively. Numerous pathologies of the corpus callosum are encountered during CT and MRI. The aim of this study is to facilitate a better understanding and thus treatment of the pathological entities of the corpus callosum by categorising them according to their causes and their manifestations in MR and CT imaging. Familiarity with its anatomy and pathology is important to the radiologist in order to recognise its disease at an early stage and help the clinician establish the optimal therapeutic approach.

[Diffusion-weighted MR imaging of the brain]

Imaging of water diffusion or diffusion-weighted MR imaging provides physiological information about brain diseases that cannot be obtained from conventional sequences. This technique is very sensitive for the detection of cerebral ischemia from arterial origin and can distinguish cerebral ischemia from other non-vascular brain pathologies in patients presenting with abrupt onset of focal neurological deficit. Diffusion-weighted imaging is used for the evaluation of non-vascular diseases as well. Combined with conventional sequences, it is helpful to differentiate brain abscesses from necrotic tumors. Quantitative diffusion-weighted imaging provides additional information in the characterization of tumors or inflammatory, degenerative and metabolic lesions. Finally, diffusion-weighted imaging data also has prognostic value.

Suivi évolutif d’une myelinolyse centro-pontique en IRM de tenseur de diffusion et de tracking de fibres

OBJECTIVES

To illustrate the value of diffusion tensor imaging and tractography in the diagnosis and follow-up of central pontine myelinolysis.

CASE REPORT

We report a case of central pontine myelinolysis in a 29 year old woman, also anorexic, studied using MR Diffusion Tensor Imaging (DTI) and Fibre Tracking (FT) focused on the pons, and compared with the studies of 5 normal volunteers. Tractography showed a swollen aspect of the right corticospinal fiber tract correlating with mild left lower extremity deficit at clinical evaluation. The pontine fibers were posteriorly displaced but intact. The sensory tracts were also intact. Apparent Diffusion Coefficient values were increased and Fractional Anisotropy was decreased in the lesions. Follow up imaging showed persistent abnormal ADC and FA values in the pons although the left cortico-spinal tract returned to normal, consistent with the clinical outcome.

CONCLUSION

Diffusion Tensor Imaging MR and Fiber tractography are a new method to analyse white matter tracts. It can be used to prospectively evaluate the location of white matter tract lesions at the acute phase of central pontine myelinolysis and follow up.

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.