OBJECTIVESTo assess the diagnostic accuracy and to study the histologic typing of mediastinal lesions using core needle biopsies.

METHODSThe histopathology and immunophenotype of 65 mediastinal core needle biopsy specimens were studied retrospectively by light microscopy and immunohistochemical staining (ABC method). Gene rearrangement studies were performed in some of the non-Hodgkin's lymphomas cases using PCR. Follow-up records were also analyzed.

RESULTSMorphologically, all specimens showed a combination of epithelioid cells, lymphoid cells and fibrous tissue in different proportions. The pathologic diagnoses included lymphoma (21 cases), pulmonary carcinoma (20 cases), thymoma (14 cases), thymic carcinoma (4 cases), seminoma (3 cases) and chronic inflammation (1 case). Definitive diagnosis was not possible in 2 cases due to insufficient material. The tumor cells in lymphoma (21 cases) expressed CD20, CD3, TDT, CD30, CD15 or EMA, depending on their histologic subtypes. Tumor cells in the 17 pulmonary carcinoma cases expressed cytokeratin (CK), except 3 cases of small cell carcinoma of lung. Synaptophysin, chromogranin A and neuron-specific enolase were all positive in the 10 cases of small cell carcinoma of lung and 1 case of thymic small cell carcinoma (which was also CD5 negative). The 3 cases of adenocarcinoma of lung showed positivity for thyroid transcription factor-1 (TTF-1) and they were negative for CD5. The 14 thymoma cases expressed CK, CD3 or CD20. The 3 thymic carcinoma cases expressed CK and CD5. Placental-like alkaline phosphatase (PLAP) was positive in 3 seminoma cases which were CK-negative. Immunoglobulin heavy chain gene was rearranged in the 3 cases of diffuse large B-cell lymphoma and 1 B-cell anaplastic large cell lymphoma case. T-cell receptor beta gene was rearranged in 5 T-cell lymphoblastic lymphoma cases.

CONCLUSIONSMicroscopic assessment of tissue samples from mediastinal core needle biopsies should be made in combination with clinical and radiologic information. Ancillary investigations, including immunohistochemical staining and/or gene rearrangement studie, are needed in both non-lymphoma and lymphoma cases of mediastinum.