Presentation
First seizure.
Patient Data
A region of hypoattenuation is seen within the left superior frontal gyrus with a 20mm ring enhancing lesion evident on the post contrast images. Remaining intracranial appearances are unremarkable.
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.
Incomplete ring enhancement sign (orange arrow) suggestive of active demyelination. The enhancement is seen on the active side of demyelination which faces away from the grey matter.
Dawson's fingers - linear demyelinating plaques arranged perpendicular to the lateral ventricles like fingers (blue arrows).
This appearance is typical of multiple sclerosis.
Case Discussion
CT images show a 20mm ring enhancing lesion within the left superior frontal gyrus for which the differential diagnosis is broad (see mnemonic MAGIC DR), but most commonly would between cerebral metastasis, GBM and cerebral abscess.
The MRI study shows the lesion to have incomplete ring enhancement on the coronal images and reveals multiple other non-enhancing T2/FLAIR white matter lesions with the characteristic Dawson's fingers appearance of multiple sclerosis.
Occam's razor would favor the ring enhancing lesion to be tumefactive MS / active demyelination, but given the superficial location of the enhancing lesion and that it was not involving eloquent cortex, a biopsy was performed for confirmation. The pathologist was able to confirm active demyelination at this site.
MICROSCOPIC DESCRIPTION: The biopsy pieces comprise cerebral cortex and white matter. Focally there is a well-demarcated white matter abnormality comprising a heavy infiltrate of macrophages accompanied by smaller numbers of lymphocytes and reactive astrocytes. Small blood vessels within this area are surrounded by a lymphocytic infiltrate. The Luxol fast blue stain shows loss of myelinated axons within this region. There is no atypia of the glial cell and mitotic figures are not seen. There is no necrosis. The features are of acute/active demyelination. There is no malignancy.
DIAGNOSIS/COMMENT: Left frontal lesion, biopsy - Features of acute/active demyelination.
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