Intense focal pituitary FDG uptake due to intravascular large B‐cell lymphoma in pyrexia of unknown origin
Authors: David A. Pattison, Michael S. Hofman, Ali Bazargan, Peter Colman, Rodney J. Hicks
Journal: American Journal of Hematology (2016)

Intravascular large B-Cell lymphoma (IVLBCL) is a rare extranodal lymphoma characterized by the presence of neoplastic lymphocytes in the lumina of small vessels 1. Diagnostic delay (often made post-mortem) is at least in part responsible for its poor prognosis. We present two cases with pyrexia of unknown origin (PUO) despite exhaustive prior investigation (repeated radiologic, serological, and bone marrow biopsy) and prolonged inpatient admission referred for 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT). Intense pituitary uptake (SUVmax = 9.9) without abnormality on co-registered CT was the dominant finding in Case 1 (Image 1A), a 58-year-old man with nine-month history of fevers, 20 kg weight loss, raised inflammatory markers, and pancytopenia. Magnetic resonance imaging (MRI) excluded pituitary macroadenoma and transphenoidal-surgical biopsy was diagnostic for IVLBCL with CD20 + ve staining in small arterioles (Image 1B) but complicated by panhypopituitarism. Case 2 is a 63-year-old man hospitalized with a six-week history of fever, weight loss, raised inflammatory markers, anemia, and thrombocytopenia. A similar finding of focal pituitary FDG uptake (SUVmax = 7.1, Image 1C), raised suspicion of IVLBCL that was subsequently confirmed by CD20 + ve staining of bone marrow biopsy (Image 1D). MRI pituitary was unremarkable and repeat FDG PET/CT after 5 cycles of R-CHOP demonstrated complete resolution of previously intense pituitary uptake. Both patients remain in complete remission at 68 months and 31 months following diagnosis, respectively. IVLBCL demonstrates highly varied clinical presentation and end-organ involvement with FDG uptake abnormalities described in bone (focal or diffuse), kidneys, spleen, liver, meninges, or stomach 2, 3; however isolated focal pituitary uptake has not been reported. It is critical that referring clinicians and reporting nuclear medicine physician recognizes the significance of intense pituitary FDG uptake in this context, as the diagnosis of IVLBCL may be confirmed by identification of CD20 + ve cells on random skin biopsy 4, avoiding the risk of potentially unnecessary pituitary surgery. The intravascular disease process rarely results in macroscopic parenchymal involvement or lymphadenopathy and thus limits the role of conventional morphologic imaging in the diagnosis of IVLBCL; however functional imaging with FDG PET/CT is useful to identify sites of hypermetabolic disease. FDG PET/CT has also been shown to be a sensitive 5 and cost-effective 6 test to localize the source of PUO, and we recommend early use of FDG PET/CT in this setting to avoid diagnostic delay. A,C: Sagittal fused FDG PET/CT and FDG PET images demonstrate focal intense pituitary uptake. B: Transphenoidal pituitary biopsy, with CD20 + ve immunohistochemical staining of small vessels. D: Bone marrow trephine, CD20 + ve immunohistochemical staining associated with small vessels.