Thymoma, Lymphocyte-Rich, Mimicking T-ALL

Siba El Hussein, MD
2 min readMar 12, 2022

Lessons From the Friday Unknowns

The patient presented with newly identified large right lung mass and an unremarkable complete blood count.

Touch imprints of the biopsy specimen show numerous intermediate lymphoid cells with oval nuclei, fine chromatin, small nucleoli and scant cytoplasm, in a background small mature lymphocytes.

Histologic sections show small fragments of tissue composed of numerous small lymphoid cells with fine chromatin and occasional large cells with pale chromatin.

The lymphoid cells are positive for CD1a, CD2 (weak), CD3, CD4, CD5, CD7 (weak), CD8 and TdT, and are negative for CD20 and CD34.


The antibody specific for CD20 highlights some dendritic cells


The antibody specific for cytokeratin highlights larger cells arranged in irregular networks typical of thymic epithelial cells.


The results of flow cytometry immunophenotypic data showed 40% immature T-cells. In the histograms, the T-cells show a pattern suggestive of continuous maturation consistent with reactive thymocytes.

In summary, these findings support the diagnosis of thymoma. The neoplasm is lymphocyte-rich. The biopsy specimen is quite small and therefore the classification of this neoplasm or the possibility of potential invasion cannot be fully assessed.

Link to digital slides: | Case 5

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Siba El Hussein, MD

Hematopathology | Cytopathology | Molecular pathology | Digital pathology | Data science | Machine learning