Neurosyphilitic gumma on F18-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography: an old disease investigated with a new technology.

Neurosyphilitic gumma is a slowly progressive inflammatory manifestation of tertiary syphilis. It is characterised by chronic granulomata that ranges from microscopic lesions to large tumour-like masses. While cutaneous, mucosal and skeletal gummatous lesions are not uncommon, neurosyphilitic gumma is rare. F18-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) has been used effectively to assess the metabolic nature of brain masses, in particular in guiding biopsy and grading gliomas. However, the inflammatory nature of lesions such as neurosyphilitic gumma poses challenges to diagnostic imaging modalities including CT scans, MRI and PET. Since FDG is not a specific tracer for malignancy, neurosyphilitic gumma can mimic a high-grade glioma by demonstrating intense FDG uptake and is therefore a potential diagnostic pitfall. We report a case of neurosyphilitic gumma identified on FDG PET.