Nondetection of Sentinel Lymph Node with Lymphoscintigraphy as a Result of Massive Malignant Invasion Shown by Positron Emission Tomography

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Abstract
The authors report the complementary roles of lymphoscintigraphy in sentinel node mapping and F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in a massively invaded sentinel node. A 49-year-old woman was referred to the authors’ institution after the resection of a malignant melanoma (Clark IV, Breslow 5.25) of the right buttock. No evidence of regional or distant organ metastases was observed on bone scintigraphy or thoracoabdominal or cerebral computed tomographs. Preoperative lymphoscintigraphy showed drainage around a circular structure, without any node detected. F-18 FDG PET imaging detected an area of focal, markedly hypermetabolic activity at the same location. The focal, markedly hypermetabolic activity detected by F-18 FDG PET corresponded to a massively invaded sentinel node not shown by lymphoscintigraphy but found and removed at the time of surgery. Radical regional lymphadenectomy showed only one small additional lymph node micrometastasis detected after immunohistochemical staining for S-100 protein and HMB45 antigen. This case emphasizes the complementary roles of lymphoscintigraphy sentinel node mapping and F-18 FDG PET. Indeed, a massively invaded sentinel node may be detected by PET but missed by lymphoscintigraphy.