Imaging Case of the Month: January 2013 Page 3

Explanation:
 

  • This is an MRI scan of a 54 year old male with global hypoxic-ischemic injury. In these patients, grey matter structures (basal ganglia, thalami, cortex, cerebellum, hippocampi) are preferentially affected because of their higher metabolic activity and increased energy demands. 
  • Diffusion weighted imaging is the most sensitive modality for early detection of hypoxic brain injury and will become positive within hours of an ischemic event. FLAIR and T2 abnormalities, are often more subtle and may not be evident in the first 24 hrs. 
  • Common etiologies of hypoxic-ischemic injury in adults are acute near drowning, cardiac infarctions (answer choice C), and acute asphyxiation.
  • A similar pattern may also be seen in patients with Creutzfeldt-Jakob disease (CJD), a spongiform encephalopathy characterized by rapidly progressive dementia, myoclonus, and death (answer choice B).  The pathophysiology of CJD is mediated by infectious prions, which are a type of protein that can alter the structure of neighboring proteins.  Imaging findings in sporadic CJD include FLAIR/T2 signal abnormality and restricted diffusion in the basal ganglia (putamen more commonly affected than globuspallidus) and cerebral cortex. The thalamus may be involved in variant CJD.
  • Answer A suggests the diagnosis of posterior eversible encephalopathy syndrome (PRES). Imaging findings include T2/FLAIR abnormalities of the cerebral cortex and subcortical white matter, with a predilection for posterior circulation. Basal ganglia involvement is rare and diffusion restriction is not commonly seen.
  • Answer D is a red herring for those distracted by the cystic area in the right middle cranial fossa and thought it may represent encephalomalacia from a chronic infarct. The cystic area actually represents an arachnoid cyst without significant mass effect on surrounding structures. In either case, the finding is incidental and the FLAIR/ DWI abnormalities described above are the pertinent findings.
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