18F-Fluciclovine (18F-FACBC) PET/MRI Findings in Tumefactive Demyelinating Lesion: A Case Report.

A 28-year-old man presented with acute onset dysarthria and right facial droop. MRI revealed a horseshoe-shaped mass in the left frontal lobe, and tumefactive demyelinating lesion (TDL) was suspected. Despite steroid pulse therapy, follow-up imaging demonstrated lesion enlargement, raising concern for malignancy. 18F-Fluciclovine (18F-FACBC) PET/MRI showed moderate tracer accumulation. Surgical resection was performed, and the diagnosis of TDL was confirmed. This represents the first reported case of TDL evaluated with 18F-Fluciclovine PET imaging. The discordance between moderate tracer uptake and rapid lesion growth may be useful for differentiating TDL from glioma.