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 favour 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.