Abstract

Thymic epithelial tumors are the uncommon mediastinal tumors but are the most common primary tumors of the anterior mediastinum. Computed tomography (CT) is the imaging modality of choice for assessment in patients suspected thymic epithelial tumor. The objectives of this study were to assess the CT features of various types of thymic epithelial tumors on the basis of the 2004 WHO classification and to identify the specific CT findings for differentiation between each thymic epithelial tumor. A retrospective study reviewed CT findings of 35 patients with thymic epithelial tumors, who underwent surgical resection from January 2010 to April 2017 and had available pre-operative chest CT study. The tumors were reclassified into six types of thymic epithelial tumors (A, AB, B1, B2, B3 and thymic carcinoma) on the basis of the 2004 WHO classification system. The CT findings including the size (longest diameter), margin, shape, presence of focal area of low attenuation of necrosis or cystic change, mediastinal fat invasion, great vessels invasion, degree and pattern of tumor enhancement, presence of tumor calcification and presence of mediastinal lymphadenopathy (short axis diameter more than 10 mm), the presences of pleural effusion, pleural mass, pulmonary nodule, pericardial effusion and extrathoracic metastasis were evaluated. Our study consisted of 20 (57.14%) men and 15 (42.86%) women, age 15-78 years (mean 51.25 years). Pathological proven into 30 thymomas (85.71%) and 5 cases (14.29%) of thymic carcinomas. The 30 thymomas were classified according to WHO classification; type A in 5 (14.29%), type AB in 4 (11.43%), type B1 in 5 (14.29%), type B2 in 9 (25.71%), and type B3 in 7 (20%) patients. The tumor sizes of type A, AB, B1, B2 and B3 thymomas and thymic carcinoma were 6.2±1.97, 8.1±2.17, 4.9±2.47, 6.8±3.04, 4.7±1.87, and 9.6±2.78 cm, respectively. No definite CT manifestation that distinguishes between each different WHO pathological type of thymoma with statistical significance. The tumor dimension > 8 cm, irregular margin, mediastinal fat invasion, great vessel invasion, lymphadenopathy, pericardial effusion and extrathoracic metastasis could differentiate between thymoma and thymic carcinoma (P-value <0.05). Great vessel invasion and extrathoracic metastasis had high sensitivity (80%), specificity (100%), PPV (100%) and NPV (96.77%) for diagnosis thymic carcinoma. No definite CT manifestation that distinguishes between each different WHO pathological types of thymomas. Tumor size more than 8 cm, irregular margin, presence of mediastinal fat invasion, great vessel invasion, mediastinal lymphadenopathy or extrathoracic metastasis favors the diagnosis of thymic carcinoma.

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