A 32-year-old woman presents with acute vision loss in the left eye and weakness in the right lower limb over 2 weeks. MRI brain shows multiple ovoid lesions perpendicular to the lateral ventricles in the region marked **A** (centrum semiovale), along with similar lesions in the cervical spinal cord. CSF shows oligoclonal bands. Which of the following imaging features would be MOST characteristic of this patient's condition at the level marked **A**?