Early Detection of Secondary Central Nervous System Lymphoma on PET/CT

We present a case of secondary central nervous system relapse of lymphoma detected initially on PET/CT without corresponding findings on MRI. A 60-year-old lymphoma patient demonstrated an FDG-avid focus in left cerebellar hemisphere on restaging PET/CT. MRI brain showed no corresponding abnormality, and expectant management ensued. Six months later, she represented with metabolic progression of previously seen FDG-avid focus in left cerebellar hemisphere, now also manifesting as an enhancing mass on MRI. Posttreatment scan for presumed lymphoma relapse showed metabolic response. This case demonstrates the advantage of PET/CT over anatomical imaging to detect metabolic changes before structural changes become apparent.