[Correlation of World Health Organization classification of thymic epithelial tumors to their CT features]

Thymic epithelial tumors have a broad spectrum of biologic and morphologic features. This study was to assess the CT features of various subtypes of thymic epithelial tumors on the basis of the 1999 World Health Organization (WHO) classification.

CT features of thymic epithelial tumors in 94 patients were retrospectively analyzed. All cases were confirmed histologically according to the 1999 WHO classification, including 7 cases of type A, 24 cases of type AB, 16 cases of type B1, 13 cases of type B2, 16 cases of type B3, and 18 cases of type C.

In the 94 cases, the long- and short-axis diameters of type A and type AB tumors were significantly shorter than those of type C tumors (P<0.05). All type A tumors had smooth contours, type A, AB, and B1 tumors were likely to have smooth contours (P<0.05), while type B3 and C tumors were likely to have irregular contours (P<0.05). Type A tumors had less necrotic areas than any other types (P<0.05). Multiple calcifications were more frequently seen in type B2, B3, and C tumors than in type A, AB, and B1 tumors (P<0.05). Homogeneous enhancement was more frequently seen in type A, AB, B1, and B2 tumors than in type B3 and C tumors (P<0.001). Type B3 and C tumors significantly preferred to infiltrate into mediastinal fat than any other types (P<0.05).

Though CT features of different subtypes of thymic epithelial tumors according to WHO classification are overlapped, short diameter, smooth contour, round shape, homogeneous density, and homogeneous enhancement are most suggestive for type A tumor; large diameter, irregular contour, necrosis and multiple calcifications in the lesion, heterogeneous enhancement, mediastinal fat infiltration, and great vessel infiltration are most suggestive for type B3 and C tumors.