Fine-needle aspiration cytology and differential diagnoses of fibrolamellar hepatocellular carcinoma metastatic to the mediastinum: case report

We report a case of fibrolamellar hepatocellular carcinoma (FL-HCC) that metastasized to the posterior mediastinum. The diagnosis was made on fine-needle aspiration biopsy (FNAB). The cytologic features were characterized by the presence of large, dishesive, polygonal cells with granular cytoplasm and well-defined cell outlines resembling oncocytes. Groups of neoplastic hepatocytes containing bile pigment were also noted. The diagnosis of FL-HCC in a metastatic site can pose diagnostic challenges on FNAB. The cytologic features overlap with a variety of tumors that have oncocytic features and also with melanoma and paraganglioma. Recognition of specific cytologic features of FL-HCC can facilitate accurate diagnosis in a metastatic site. The cytologic findings and differential diagnoses of FL-HCC that metastasized to the posterior mediastinum are discussed.