Diffusion-weighted MRI and ^99mTc-HMPAO SPECT in delayed relapsing type of carbon monoxide poisoning: Evidence of delayed cytotoxic edema

Background: Carbon monoxide (CO) is a common cause of poisoning, and its sequelae include a progressive (25%) and a delayed relapsing form (75%). We report the diffusion-weighted MRI (DWI) findings in the delayed relapsing form of CO poisoning and characterize the types of edema. Methods: From November 1, 2000 to June 1, 2003, 5 consecutive patients (2 men, 3 women, range of age: 54-67 years), who had the delayed relapsing type of CO poisoning, underwent DWI, conventional MRI, MR angiography and SPECT. CO poisoning was diagnosed by the presence of a typical clinical history, an abnormally increased level of serum carboxyhemoglobin and MRI findings. Apparent diffusion coefficient (ADC) values were measured in all of the abnormal lesions with visual inspection of DWI and T ₂-weighted echo-planar imaging. Results: DWI showed high signal intensities in bilateral periventricular white matter, in the splenium of the corpus callosum, in internal capsules, and brainstem showing moderately decreased ADC values. In the globus pallidus, the ADC values were rather increased with low signal intensities on DWI. Brain SPECT showed decreased perfusion in bilateral white matter and some parts of the cerebral cortex, which correlated well with the DWI findings. Conclusions: We suggest that prominent, symmetric restricted diffusion can occur in periventricular white matter, brainstem, and corpus callosum after the delayed relapsing type of CO poisoning. Delayed cytotoxic edema can occur in this setting, which provides a new guidance for the pathogenesis of CO poisoning and the differential diagnosis of white matter diseases.