Lymphoscintigraphy as a result of massive malignant invasion shown by positron emission tomography

Purpose: The authors report the complementary roles of lymphoscintigraphy i n sentinel node mapping and F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in a massively invaded sentinel node. Materials and Methods: A 49-year-old woman was referred to the authors' ins titution after the resection of a malignant melanoma (Clark IV, Breslow 5.2 5) of the right buttock. No evidence of regional or distant organ metastase s was observed on bone scintigraphy or thoracoabdominal or cerebral compute d tomographs. Preoperative lymphoscintigraphy showed drainage around a circ ular structure, without any node detected. F-18 FDG PET imaging detected an area of focal, markedly hypermetabolic activity at the same location. Results: The focal, markedly hypermetabolic activity detected by F-18 FDG P ET corresponded to a massively invaded sentinel node not shown by lymphosci ntigraphy but found and removed at the time of surgery. Radical regional ly mphadenectomy showed only one small additional lymph node micrometastasis d etected after immunohistochemical staining for S-100 protein and HMB45 anti gen. Conclusions: This case emphasizes the complementary roles of lymphoscintigr aphy sentinel node mapping and F-18 FDG PET. Indeed, a massively invaded se ntinel node may be detected by PET but missed by lymphoscintigraphy.