Malignant thymoma is usually manifested as a mediastinal mass. Occasiomally, these tumors may be associated with a variety of systemic syndromes, such as myasthenia gravis, pure red cell aplasia or hypogammaglobulinemia. However, it is
generally accepted that thymomas rarely metastasize and the frequency of extrathoracic metastasis has been reported as 1 to 15% In general, nuclear changes of tumor cells such as enlarged size, irregular shape and altered textures are
determining
factors in the assessment of the grade of malignancy,
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