Case history
An 84-year-old woman presents with a mediastinal mass. Representative sections are shown.
What is the diagnosis?
- Solitary fibrous tumor
- Small lymphocytic lymphoma
- Thymoma, Type A
- Thymoma, Type AB
Answer: D. Thymoma, Type AB
Brief explanation of the answer:
The histologic findings show a lesion composed of spindle cells and lymphocytes. The spindle cells are monotonous without significant nuclear atypia. These findings are consistent with thymoma, type AB or mixed thymoma. The World Health Organization divides thymic tumors into the following categories:
Type A: Spindle cell/medullary, composed of spindle cells
Type AB: Mixed type, composed of spindle cells and lymphocytes
Type B1: Lymphocyte rich, resembling normal thymus
Type B2: Composed of polygonal epithelial cells with abundant cytoplasm and vesicular nuclei with lymphocytes
Type B3: Predominantly epithelial cells with minor lymphocyte population
Type C: Thymic carcinoma
Thymic carcinomas tend to be unencapsulated with obvious anaplastic features.
Case contributed by Diana Lin, M.D., Assistant Professor, Anatomic Pathology, UAB Department of Pathology