Fine‐needle aspiration biopsy for the diagnosis of metastatic type B thymoma to lymph nodes: A case report

Abstract

Extrathoracic metastases of thymic neoplasms are very rare (incidence is believed to be around 3–6%), and their cytologic features have seldom been reported. The most common subtype associated with metastasis is thymic carcinoma, followed by type B thymoma. The recognition of thymic metastasis is challenging because of its rarity and because of its potency to mimic tumors from other sites. We report the case of a metastatic type B thymoma in supraclavicular and mediastinal lymph nodes in a 69-year-old male diagnosed on fine-needle aspiration biopsy (FNAB). The patient had a previous history of type B (mixed or lympho-epithelial) thymoma with myasthenia treated with corticosteroids, surgery, and radiotherapy 12 years earlier. The primary tumor, partially calcified, measured 7 3 6.5 3 3 cm and involved the pericardium and periaortic fat. Surgical margins were free of tumor. The patient developed left diaphragm and left vocal cord palsy after surgery. In 2012, he was admitted to the hospital because of recurrent bilateral bronchopneumonia due to multiresistant Pseudomonas aeruginosa. The investigations revealed mediastinal (upper and middle) and left supraclavicular lymphadenopathies with left carotid artery involvement. FNAB of lymphadenopathies from both localizations was performed and liquidbased preparations (Thinprep VR ) were made. The aspirates were cellular, composed of cohesive epithelioid to spindle cells with round regular nuclei and small nucleoli showing mild atypia and pleomorphism. These cells were admixed with small mature lymphocytes (Fig. C-1A). A cell-block from one of the aspirates was made and revealed similar cohesive clusters of epithelial cells with a squamoid appearance (Fig. C-1B). Small lymphocytes were also intermingled in the clusters or admixed in the background. Immunocytochemistry was performed: the epithelial cells were positive for keratin wide spectrum (KWS) (Fig. C-1C) and negative for neuroendocrine markers (chromogranin A and synaptophysin), CD5, and TTF-1. The lymphocytes were mostly positive for CD3 and CD5 and a fraction of them was also positive for TdT (Fig. C-1D), revealing an immature phenotype. Because of the clinical history and the presence of a dual epithelial and lymphoid population closely intermixed with immature TdT positive lymphocytes, a diagnosis of metastatic thymoma was made on cytology. Thymomas are cytologically benign neoplasms of the thymus gland accompanied by varying numbers of benign lymphocytes. The proportion of lymphocytes and epithelial cells determines the type of thymoma (A, B1, B2, B3). The epithelial cells are almost always negative for CD5. By contrast, thymic carcinomas are by definition composed of cytologically malignant cells, often positive for CD5. A peculiar feature of thymoma but not thymic Division of Clinical Pathology, Geneva University Hospital, Geneva, Switzerland Center of Oncology, Geneva University Hospital, Geneva, Switzerland Cantonal Institute of Pathology, Sion, Switzerland *Correspondence to: Marc Pusztaszeri, M.D., Service de Pathologie Clinique, Hopitaux Universitaires de Geneve, 1 rue Michel-Servet, 1211 Geneve 14, Switzerland. E-mail: marc.pusztaszeri@hcuge.ch Received 9 July 2012; revised 26 November 2012; Accepted 1 January 2013 DOI: 10.1002/dc.22965 Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com).