The value of core needle biopsy in differential diagnosis of mediastinal T lymphoblastic lymphoma and type B1 thymoma

Objective　To analyze the clinical and pathological characteristics of T lymphoblastic lymphoma (T-LBL) and type B1 thymoma in the mediastinum, and to improve the accuracy of differential diagnosis between two diseases. Methods　 Pathology of consecutive 34 cases of T-LBL and 10 cases of type B1 thymoma were reviewed in this study. All the initial diagnosis was made with core needle biopsy specimens of mediastinal masses and confirmed by subsequent chemotherapy and/or excision biopsy specimens. The clinical and pathological features of T-LBL and type B1 thymoma were compared by reviewing clinical records and analysis of HE and immunohistochemical staining sections. The chi-square test was used for statistic analysis. Results　The mean age of the patients with type B1 thymoma was 43 years, and the ratio of male to female was 2:3, while the patients with T-LBL were much younger (with mean age of 25, 73% of them younger than 30 years old) and the male to female ratio was 3.3:1. All the T-LBL cases presented symptoms including chest tightness, shortness of breath and cough. Three patients of thymoma complained of chest tightness and shortness of breath, and 2 cases presented symptoms of myasthenia gravis. Imaging examination showed solitary mass in anterior mediastinum in patients of both groups, 88% of the T-LBL patients had mass>10cm, while accounting for 50% in B1 thymoma patients. Concurrent pleural effusion was only observed in the T-LBL patients. Histopathologically, T-LBL and thymoma showed significant differences, including the infiltration of tumor cells in fibrous tissue (65% in T-LBL vs 0% in thymoma), invasion of peripheral fat tissue (59% vs 20%), invasion of skeletal muscle (41% vs 0%), tumor necrosis (21% vs 0%), and remaining of thymus lobular structure was found in only 3% of T-LBL. Intact cytokeratin network was shown in B1 thymoma (100%) by immunohistochemical staining. Conclusions　Patients' gender, age, clinical features and imaging features, especially pathological characteristics were remarkable different between T-LBL and type B1 thymoma. Combining clinical manifestations and pathological changes will help to improve the accuracy of core needle biopsy in differential diagnosis of T-LBL and thymoma.