Cytologic patterns of metastatic thymoma: diagnosis by fine-needle aspiration biopsy

Thymomas are the most frequent primary tumors of the anterior mediastinum. These lesions are slow growing and can be locally invasive, but extrathoracic metastases are rare, occurring in less than 2% of cases. Fine-needle aspiration biopsy (FNAB) may be helpful in making the diagnosis of metastatic thymoma, with or without a clinical history of primary mediastinal thymoma. We report three cases of metastatic thymoma diagnosed by FNAB. Each case illustrates a distinctive cytologic pattern. While two of the patients had a history of histologically confirmed thymoma 11 and 13 years previously, a third patient presented with an enlarged supraclavicular lymph node and pulmonary nodules, and no prior diagnosis of thymoma. These cases demonstrate that based on distinctive cytologic patterns and features, a diagnosis of metastatic thymoma can be made with FNAB. Ancillary studies will often confirm the diagnosis.