Lobectomy for subsegmental lymph node metastasis of unknown origin

We report a very rare case of resected subsegmental lymph node metastasis of unknown origin. Hilar (N1) lymph node metastasis of unknown origin has previously been reported, but intrapulmonary lymph node metastasis has not been reported to date. At this patient's first visit to our hospital, an abnormal nodule was found on the upper lung lobe on a chest radiograph. After 4 years' follow-up, the nodule vanished. but a tiny nodule had emerged. 2-Fluoro-2-deoxy-D-glucose positron-emission tomography (FDG-PET) computed tomography was performed, and abnormal accumulation was observed only in the newly emerged intrapulmonary nodule. Right upper lobectomy was performed and a metastatic subsegmental lymph node, but no primary lesion, was found. Our observations suggest that evanescence of a suspicious primary lesion indicates the possibility of metastasis. FDG-PET was useful in this case for detecting lymph node metastases and demonstrating that the primary and further metastatic lesions were absent.