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Encephalopathies encompass a wide range of etiologies, including intoxications, autoimmune disorders, and metabolic imbalances. Symptoms are often nonspecific and range from seizures, focal neurological deficits, and movement disorders, to coma, permanent sequelae and death.1 MRI is the imaging modality of choice and is often the first indicator of an encephalopathy as a possible cause of symptoms.1 Recognition of distinct MRI enhancement patterns in regard to symmetry and topographic distribution can help identify the underlying pathology.
This article highlights the vital role the radiologist plays in identifying these manifestations, which in some cases are reversible. We also illustrate the most common toxic, autoimmune, and metabolic encephalopathies to create an understanding and awareness of typical imaging appearances the radiologist may encounter (Table 1).
Toxic Etiologies
Thermatrim Encephalopathy
Thermatrim, a thermogenic dietary supplement marketed to promote weight loss, has been associated with anxiety, insomnia, cardiovascular disorders, and central nervous stimulation.2 Imaging findings are characteristic for extensive symmetric involvement of the corpus callosum, pons, and the subcortical white matter, with hyperintensities on T2-weighted imaging (T2-WI) and restricted diffusion on Diffusion Weighted Imaging (DWI) with reduced Apparent Diffusion Coefficient (ADC) values (Figure 1).2
Methanol Encephalopathy
The clinical presentation usually involves visual disturbances as a first symptom followed by headaches, dizziness, malaise, seizures, stupor, and coma after a latent period.3 Intoxication can be fatal unless treated early and characteristically involves bilateral necrosis of the putamina with or without hemorrhage.4 Variable signal intensities on T1-weighted imaging (T1-WI) with enhancement after contrast administration, hyperintensities on T2-WI, and Fluid Attenuation Inversion Recovery (FLAIR) sequences, and restricted diffusion on DWI, are typical imaging findings (Figure 2).4
Carbon Monoxide Encephalopathy
Carbon-monoxide intoxications may be accidental or intentional and present with nonspecific symptoms and signs ranging from headaches and confusion to coma and death.4 Exposure can be acute or chronic, and bilateral symmetric necrosis of the globi pallidi with or without involvement of the caudate and putamina is characteristic.4 Hypointensities on T1-WI and hypertintensities on T2-WI are distinct imaging findings and their extent correlates with clinical outcome (Figure 3).4
Heroin Encephalopathy
Heroin can be administered through multiple routes, including intravenous injection, oral use, and vapor inhalation, also referred to as "chasing the dragon." Leukoencephalopathy related to heroin vapor inhalation progresses from cerebellar signs and motor restlessness to...