[A comparative clinical and pathological study on the classification and prognostic features of 57 thymomas. I. Microscopy and ultrastructural pathology (author's transl)].

Fifty-seven thymomas, defined as neoplasms of the epithelial-reticular framework cells of the thymus, were assessed in respect to histologic type, inclusive of there ultrastructural aspects. The median age of the 57 patients was 40.4 years, with a range of 2 1/2--72 years. All neoplasms were located in the anterior mediastinum. The tumours in 40 cases were encapsulated and without invasion of adjacent tissue or implants (equal to non-invasive thymomas). The tumors in 17 cases were invasive of adjacent tissue, particularly mediastinal pleura, pericard and trachea. Six of 57 patients (equal to 10.5%) with thymomas have had a thoracic and supraclavicular lymph node metastasis, and osteolytic metastases in the vertebrae and sternum. Thirty-seven (equal to 64.9%) were so-called lympho-epithelial, 7 (equal to 12.3%) pure epithelial, 4 (equal to 7.0%) atypical (or anaplastic) with granulomatous focuses, 3 (equal to 5.3%) carcinoid and one (equal to 1.8%) seminomatous tumors. One patient have had a thymic cyst as a tumor-like conditions of the thymus, and four patients (equal to 7.0%) have had a thymo-lipoma. The histologic type of thymoma had no proof value in predicting prognosis with the exception of the so-called atypical or anaplastic thymoma. The fine structural aspects of thymomas and the fine structural differential diagnosis of anterior mediastinal tumors are discussed.