18F‐choline radiotracer positron emission tomography as a new means to monitor central nervous system lymphoma

Abstract

Whilst monitoring a 60-year-old woman with primary central nervous system (CNS) lymphoma who had a permanent pacemaker in situ, we found that F-choline positron emission tomography/computed tomography (PET/CT) has potential as a surveillance modality. The patient had initially attended with right-leg weakness, receptive dysphasia and memory impairment. Contrast-enhanced CT of the head demonstrated a large biparietal cerebral mass (left image). Biopsy was planned, but due to worsening symptoms corticosteroids were commenced five days before the procedure. The patient had an excellent clinical response with a further head CT at the time of biopsy showing a partial radiological response. A biopsy found lymphocytic infiltrates, increased B cells and occasional atypical cells suspicious for treated lymphoma. Cerebrospinal fluid (CSF) analysis was normal. CNS lymphoma was diagnosed based on initial radiology and steroid response. Subsequent CT, magnetic resonance imaging (MRI) and F-choline PET/CT (central image) found no evidence of recurrence. In view of the resolution, a plan was made for close clinical and radiological monitoring rather than systemic treatment. Given the need to disable the permanent pacemaker before MRI, with the consequent logistical and safety issues, F-choline PET/CT was chosen as the surveillance modality. Contrast enhanced CT does not have the requisite sensitivity. PET imaging conventionally utilises fluorodeoxyglucose (FDG) but in the context of imaging CNS lymphoma, high physiological uptake of glucose by normal brain parenchyma limits interpretation. Dysregulated choline metabolism is, on the other hand, synonymous with oncogenesis and cancer progression. Combining choline with a fluorine-18 isotope gives PET images which provide CNS tumour depiction superior to conventional FDG (right image, example of CNS lymphoma on F-choline PET/CT imaging). In the present patient, the modality allowed close monitoring without requiring pacemaker disablement for MRI. More broadly, it highlights the potential for using F-choline PET/CT as a new CNS lymphoma monitoring tool (also addressing nephrogenic and deposition concerns with MRI gadoliniumbased contrast agents).