A 32-year-old man with cyanotic congenital heart disease (uncorrected) presents with a 2-week history of progressive headache, low-grade fever, and focal left-sided weakness. MRI brain with contrast shows a ring-enhancing lesion in the right MCA territory with surrounding vasogenic edema and mass effect. Diffusion-weighted imaging (DWI) shows the lesion core marked **A** is hyperintense with restricted diffusion (low ADC). Which of the following best explains the imaging findings at the structure marked **A**?