A case of central nervous system lymphomatoid granulomatosis; characteristics of PET imaging and pathological findings.

Lymphomatoid granulomatosis (LYG) in the central nervous system (CNS) is an uncommon lymphoproliferative disorder with low grade malignant potential. Here we report a case of CNS-LYG, in particular, its characteristics of radioisotope imaging and pathological findings. A 65-year-old man complained of visual disturbance and homonymous hemianopsia was designated. CT and MRI revealed an edematous, enhanced irregular and nodular lesion in the right occipital and parietal lobes. Although 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) scan showed low uptake in the lesion, Methionine (MET)-PET scan indicated high uptake. Proton magnetic resonance spectroscopy ((1)H-MRS) at 3T revealed a decrease of the peak of the N-acetylaspartate (NAA), suggesting a possible neoplastic lesion. The patient was diagnosed with CNS-LYG based on the surgically removed material showing perivascular infiltration of CD3-positive small T-lymphocytes with granulomatous lesions. The post-operative steroid therapy was effective and the recurrence or exacerbation has not been observed by radiological imaging until now.