Frontal Tumefactive Demyelinating Lesion Mimicking Glioblastoma Differentiated by Methionine Positron Emission Tomography.

BACKGROUND: Tumefactive demyelinating lesion (TDL) is often reported as a rare variation of multiple sclerosis (MS). TDL is difficult to diagnose solely by magnetic resonance imaging (MRI) in patients with no history of MS. This is because the lesion often shows ring enhancement with perifocal brain edema on gadolinium MRI, thus mimicking glioblastoma multiforme (GBM).

CASE DESCRIPTION: A 54-year-old healthy woman complained of headache 1 month before admission. She developed a decline in cognitive function, decreased attention, and executive function disorder 10 days before admission. Gadolinium magnetic resonance imaging showed a ring-shaped enhancement accompanied by massive brain edema in the left frontal lobe. This suggested GBM, but methionine positron emission tomography (MET PET), surprisingly, showed no uptake with a tumor-to-normal brain ratio of 1.18. Accordingly, we eliminated GBM and suspected brain abscess because diffusion-weighted images showed high signal intensity in the lesion. Although we performed drainage, we could not demonstrate the presence of pus. Pathologic analysis of a specimen obtained by needle biopsy revealed broad necrosis and a small number of inflammatory cells. We therefore prescribed steroid therapy, by which symptoms gradually improved. No relapse occurred for 2 years. We finally diagnosed the patient as having TDL.

CONCLUSIONS: MET PET is considered a possible diagnostic modality for demyelinating disease as it can appropriately reflect pathologic findings. MET PET will facilitate decision making regarding surgery in patients with TDL.