Emperipolesis as a key feature in imprint cytology of the thymus. A report of two cases.

BACKGROUND

Imprint cytology of the thymus has not received much attention. Cytology of the thymus is important because the uninvolved thymus may be needled during aspiration procedures.

CASES: In two cases, during surgery for carcinoma of the thyroid, we received thymic tissue mistakenly sampled as a pretracheal lymph node for frozen section to rule out metastasis. Imprint smears were studied. The presence of thymocytes in the cytoplasm of thymic epithelial cells (emperipolesis) was the most significant feature in the imprints. However, it was not detected on histology.

CONCLUSION

Thymic epithelial cells provide mechanical support and play a major role in the maturation of lymphocytes (thymocytes). They are observed as emperipolesis on imprint cytology. Its utility in identifying thymic cells in aspiration cytology needs to be investigated.