The brain is highly susceptible to a number of acquired metabolic abnormalities, and the list of toxins and poisons that affect the CNS is long ( Table 1). By allying imaging patterns with some clinical findings, it is possible to reach a hypothesis with good accuracy ( 2). Thus, correlations with clinical history are of particular importance in guiding imaging analysis. Inborn errors of metabolism and hypoxia may have similar imaging features, but the presented context is usually different for these possibilities.
However, such manifestations are unspecific without adequate clinical context and can represent other conditions. Therefore, lesions with such features and distributions can be secondary to underlying toxic effects. In addition, sites with higher susceptibility include the cortical gray matter, deep gray nuclei, thalami, periventricular white matter, and corpus callosum. Bilateral and symmetric lesions with restricted diffusion, no or mild mass effects, and no enhancement are often depicted. Toxic and metabolic disorders affecting the central nervous system (CNS) usually manifest imaging characteristics and topographic distributions that should raise suspicion for such diagnoses when the clinical context is compatible. Extensive lesions involving gray matter are often related to poor prognosis and outcomes, while lesions restricted to white matter, sparing cortical and deep gray matter, can point to a reversible cause. In addition to providing a final diagnosis, imaging can provide prognostic information. Imaging plays a key role in these cases, as imaging findings can be used to diagnose the condition or narrow the differential diagnosis ( 1). These cases often demand a fast and effective management approach because they may result in permanent structural brain damage. Patients with these disorders often present to the emergency department and are diagnosed with global cerebral dysfunction presenting as acute confusional state and delirium, but commonly they are also critically ill inpatients. Toxic and metabolic brain disorders manifest secondary to derangements of a well-balanced environment encompassing metabolic substrates, neurotransmitters, electrolytes, physiologic pH levels, and blood flow, either by endogenous malfunctions or exogenous toxic effects. This article addresses some of the most challenging diagnostic issues in neuroimaging. Online supplemental material is available for this article. The most important imaging patterns are presented, and the main differential diagnosis for each pattern is discussed. Basic pathophysiologic concepts regarding cerebral edemas and their relation to imaging are introduced-an important topic for overall understanding. Each pattern is suggestive of a most likely differential diagnosis, which more closely resembles real-world scenarios faced by radiologists. Conversely, this article proposes a systematic approach to address this group of diseases based on the most important imaging patterns encountered in clinical practice. Nonetheless, toxic and metabolic brain disorders in the literature are usually approached in the literature by starting with common causal agents and then reaching imaging abnormalities, frequently mixing many different possible manifestations. When an appropriate clinical situation suggests exogenous or endogenous toxic effects, the associated imaging pattern usually indicates a restricted group of diagnostic possibilities. The majority of cases demonstrate bilateral and symmetric involvement of structures at imaging, affecting the deep gray nuclei, cortical gray matter, and/or periventricular white matter, and some cases show specific imaging manifestations. Imaging plays a key role in determining the most probable diagnosis, pointing to the next steps of investigation, and providing prognostic information. Toxic and metabolic brain disorders are relatively uncommon diseases that affect the central nervous system, but they are important to recognize as they can lead to catastrophic outcomes if not rapidly and properly managed.
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