What enhancement 'sign' is seen on the coronal T1 post contrast images?
The incomplete ring enhancement sign typical of demyelination.
What diagnosis does the distribution of the non-enhancing white matter lesions suggest?
Periventricular distribution with Dawson's fingers appearance suggestive of multiple sclerosis.
MRI confirms a ring enhancing lesion within the left superior frontal lobe. The enhancing ring is slightly nodular and although it at first appears to be a complete ring on the axial images, the coronal images show that only the internal aspect of the lesions rim is enhancing (incomplete ring enhancement). There is no associated diffusion restriction.
Elsewhere within the brain there are multiple non-enhancing T2/FLAIR white matter hyperintensities which are periventricular in distribution with some showing a linear alignment away from the ventricles (perivenular arrangement) known as Dawson's fingers suggestive of primary demyelination.