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Benign metastasizing mesothelial cells: a potential pitfall in mediastinal lymph nodes.

Case Report An 18-year-old woman with an unremarkable past medical history presented after experiencing several weeks of constitutional symptoms that included weight loss and night sweats. She also complained of gradually worsening shortness of breath. On hospital admission, she was found to have a microcytic anemia and a chest x-ray showed a large soft tissue opacity obscuring the left heart border resulting in a loss of volume of the left hemithorax and elevation of the hemidiaphragm. A subsequent computed tomography scan confirmed the presence of a 12-cm predominantly solid, partially cystic anterior mediastinal mass as well as an effusion (Fig 1). An ultrasound-guided biopsy was performed initially, but the results were not conclusive. An anterior mediastinotomy was performed to obtain a biopsy of the mass. During the procedure, an enlarged left internal mammary lymph node was also noted and this was excised. Histologic review of the biopsy from the mediastinal mass showed a classical Hodgkin’s lymphoma, nodular sclerosis type 1. Sections from the enlarged internal mammary lymph node showed vascular transformation of the peripheral sinuses and marked widening of the paracortical and medullary sinuses (Fig 2). These were filled with a population composed of sheets, single cells, strips, and papillae of mesothelial cells (Figs 3, 4), which were strongly positive for calretinin (Fig 5), WT-1 (Fig 6), and desmin (Fig 7). The cells were negative for epithelial membrane antigen (EMA). The final report was of benign metastasising mesothelial cells in a lymph node; an incidental finding. The patient is currently on chemotherapy for the Hodgkin’s lymphoma.