Lymph node cancer of the mediastinum with a putative necrotic primary lesion in the lung: a case report

BACKGROUND: Although mediastinal lymph node cancer is presumed to originate in the lung, the primary site is usually unidentified, so the pathological course remains unclear. We recently encountered a case of mediastinal lymph node cancer having a putative primary lesion remaining in the lung as a necrotic focus. CASE PRESENTATION: The patient was a 56-year-old man who visited our department because computed tomography screening had revealed a nodular shadow in the lingular segment. However, on positron emission tomography, fluorine-18 deoxyglucose accumulation was detected in a subcarinal lymph node and not in the nodule in the lingular segment. Biopsy of the lung tumor and the lymph node was performed via minimal thoracotomy. Intraoperative pathologic examination showed necrosis alone and no malignant findings in the lung tumor. By contrast, carcinoma was detected in the lymph node. Additional subcarinal lymph node dissection was performed. Results of postoperative histopathologic examination indicated poorly differentiated adenocarcinoma of the subcarinal lymph node. Meanwhile, the nodule in the lingular segment was speculated to be a spontaneously resolved primary focus of lung cancer. CONCLUSIONS: In this case, the primary lung cancer focus resolved spontaneously after lymph node metastasis, explaining the pathogenesis underlying mediastinal lymph node cancer of unknown primary site. For similar cases of malignancy, aggressive treatment, including surgery, is effective.