Primary Central Nervous System Natural Killer Cell Lymphoma in a Chinese Woman with Atypical (11)C-Choline Positron Emission Tomography and Magnetic Resonance Spectrometry Findings

Primary central nervous system (CNS) natural killer (NK)-cell lymphoma is rare with only 7 cases reported previously. Magnetic resonance spectroscopy (MRS) and [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET) are frequently used for disease diagnosis and monitoring. Choline (CHO) PET is gaining popularity for identifying CNS lesions because of its high disease to background radioactivity ratio compared with FDG. Normally, CNS lymphoma shows high choline uptake on CHO-PET and a high choline peak on MRS. We present an unusual case of primary CNS NK-cell lymphoma with high choline uptake but absence of a high choline peak on MRS. A 39-year-old woman presented with subacute onset of cognitive deterioration. Magnetic resonance imaging of the brain showed a gadolinium-enhancing lesion in the left temporal lobe. MRS showed suppressed N-acetyl-aspartate and the absence of a high choline peak. CHO-PET confirmed that it was the only hypermetabolic lesion in the body with moderate uptake of choline. The differential diagnoses included encephalitis and neoplasm. She was initially treated for the former but did not respond to steroids, intravenous immunoglobulin, and plasmapheresis. A surgical biopsy later confirmed NK-cell lymphoma. She was then treated as primary CNS NK-cell lymphoma with intravenous and intrathecal chemotherapy. We presented a unique case of primary CNS NK-cell lymphoma with atypical imaging findings characterized by moderately increased uptake of choline without a corresponding high choline peak on MRS. Although CHO-PET was suggestive of malignancy, surgical biopsy was required to confirm the diagnosis.