Surgical Pathology Criteria

Micronodular Thymoma with Lymphoid Stroma

Definition

Alternate / Historical Names

Diagnostic Criteria

Supplemental Studies

Clinical

Differential Diagnosis

Type AB Thymoma Micronodular Thymoma with Lymphoid Stroma
Lymphocyte rich areas contain scattered epithelial cells Lymphocyte rich areas lack epithelial cells
Lymphocyte rich areas composed predominantly of T cells Lymphocyte rich areas contain many B cells, frequently with germinal centers

Micronodular Thymoma with Lymphoid Stroma Metastatic Carcinoma in a Lymph Node
Epithelial nodules usually scattered throughout Carcinoma usually subcapsular, sinusoidal or focal
Cytologically very bland Usually cytologically atypical
Mitotic figures very rare Mitotic figures may be numerous
Lacks a subcapsular sinus Subcapsular sinus present
Presence of adjacent nonneoplastic thymus supports a thymic neoplasm Typically no adjacent thymus
Immature T cells may be present Immature T cells absent
Rare micronodular thymic carcinomas have been reported; these show all features of micronodular thymoma but exhibit atypia and mitotic figures

Micronodular Thymoma with Lymphoid Stroma Thymic Lymphoid (Germinal Center) Hyperplasia
Small almost purely epithelial nodules with appearance of Type A thymoma alternating with B cell rich areas that frequently contain germinal centers Residual normal thymus or ribbons and nests of dendritic epithelial cells containing Hassall corpuscles
Other than the presence of germinal centers, these two do not look alike

Bibliography

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