A 55-year-old man with presumed alcohol-toxic liver cirrhosis is referred to the neurology outpatient clinic because of rapidly progressing extrapyramidal and cerebellar symptoms accompanied by disorientation. On examination a diagnosis of hepatic encephalopathy is made and the patient is treated with lactulose and neomycin. Unenhanced T1 weighted brain MRI imaging shows bilateral basal ganglia hyperintensities as depicted. In this setting, the MRI abnormality is considered to represent changes due to which of the following entities?