Diagnosis and subclassification of thymoma by minimally invasive fine needle aspiration directed by endobronchial ultrasound: a review and discussion of four cases

Thymomas have been classified by the World Health Organisation (WHO) into six groups, based on the morphology of epithelial cells and the ratio between epithelial cells and lymphocytes within the tumour. Among 1458 consecutive cases of endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) performed in a tertiary referral centre between February 2008 and February 2012, we have encountered four cases of thymic neoplasms. We discuss the cytomorphological features of three cases of type B thymoma (one each of B1, B2 and B3 subtypes) and one case of thymic carcinoma diagnosed on EBUS-TBNA using cell blocks, immunocytochemistry and flow cytometry which allowed preoperative chemotherapy to be carried out in two cases, diagnosis to be made after unsatisfactory surgical mediastinoscopy in the third and diagnosis of lymph node metastasis of the thymic carcinoma in the fourth. The differential diagnosis and criteria for subclassification of thymomas are discussed; although subclassification of these cases was possible in these cases, and tumours other than thymoma excluded, additional cases would be necessary to assess the potential accuracy of EBUS-TBNA. These, to the best of our knowledge, represent the first cases of thymoma that were diagnosed and subclassified according to WHO criteria using multimodality evaluation of EBUS-derived cytological aspirates.