This young woman clinically demonstrated features of myasthenia gravis was shown to have an anterior mediastinal mass, presumably a thymoma. It was surgically excised and confirmed to be a thymoma, type B2 (cortical).

Five thymoma subtypes can be associated with myasthenia gravis: 

1. type A (medullary)
2. type AB (mixed)
3. type B1 (organoid)
4. type B2 (cortical)
5. type B3 (well-differentiated thymic carcinoma)

Types AB, B2, and B3 thymomas are by far the most frequent subtypes and the most frequently associated with myasthenia gravis ¹.