Purpose or Case Report: The purpose of this case report is to familiarize the radiologist with the MR imaging findings of fatal heat stroke.

Heat stroke is a severe illness characterized by a core temperature > 40 degrees Celsius, with clinical manifestations of delirium, seizures, and coma, resulting from environmental exposure or physical exertion. This report focuses upon environmental, or classical, fatal heat stroke in the case of a 4 year old male who was left alone for 30 minutes in a vehicle with ambient exterior temperatures of greater than 37.8 degrees Celsius.

As a form of hyperthermia, heat stroke ensues from thermoregulatory failure in addition to systemic inflammatory and coagulation phase responses, and conceivably, from modified manifestation of heat shock proteins. Infants and young children comprise a population specifically vulnerable to heat stroke due to their large surface area to volume ratio, underdeveloped thermoregulatory system with small blood volume relative to body size, and decreased sweat production.

The CNS is especially susceptible to hyperthermia as cerebral edema and cerebrovascular congestion may lead to increased intracranial pressure, and ischemia or hemorrhage. The cerebellum is the area most sensitive to heat injury, with known direct injury to Purkinje cells, and resultant cerebellar atrophy, often leading to neuronal dysfunction, including ataxia.

MR imaging findings in heat stroke are typically multifocal reflecting the complex interplay of direct thermal injury, hypoxic ischemic injury, endothelial damage, cytokine mediated inflammation and coagulopathy.

MRI in our case of fatal heat stroke demonstrates diffuse signal abnormality within the peripheral cerebellar hemispheres (eg. Purkinje cell regions). MRI recapitulates the known pathology of fatal heat stroke with injury to Purkinge cells and adjacent Bergmann glia. Other reported heat stroke related MRI findings include T2 prolongation and restricted diffusion involving the paramedian thalamic nuclei, dentate nuclei, basal ganglia, hippocampii, and cerebral cortex particularly the vascular watershed zones.

If the health history for heat stroke is uncertain, the imaging differential diagnosis includes other cerebellar syndromes including: toxic - metabolic (eg. opiate toxicity), infectious-autoimmune (eg. Varicellar zoster cerebellitis), histiocytic neoplastic-like (eg. histiocytoses) and neoplastic (eg. leptomeningeal PNET) should be considered in the imaging differential diagnosis.
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