18 F-FAPI-04 PET/CT Outperforms 18 F-FDG in Detecting Multiple Muscle and Subcutaneous Adipose Tissue Involvement of Marginal Zone Lymphoma.

Marginal zone lymphoma (MZL) involving multiple muscles and subcutaneous adipose tissue is extremely rare. We present PET/CT findings of pathologically confirmed MZL with muscle and subcutaneous involvement in a 63-year-old man. 18 F-FAPI-04 PET/CT demonstrated significantly higher radiotracer uptake and better lesion detectability than 18 F-FDG PET/CT in all detectable lesions and, in addition, identified occult right neck muscle involvement not clearly appreciable on 18 F-FDG PET/CT. This case highlights the superiority of 18 F-FAPI-04 PET/CT over 18 F-FDG PET/CT for evaluating MZL with muscle and subcutaneous adipose tissue involvement, especially for mildly FDG-avid lesions.