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 n eedled during aspiration procedures. CASES: In two cases, during surgery for carcinoma of the thyroid, we receiv ed thymic tissue mistakenly sampled as a pretracheal lymph node for frozen section to rule out metastasis. Imprint smears were studied. The presence o f thymocytes in the cytoplasm of thymic epithelial cells (emperipolesis) wa s the most significant feature in the imprints. However, it was not detecte d on histology. CONCLUSION: Thymic epithelial cells provide mechanical support and play a m ajor role in the maturation of lymphocytes (thymocytes). They are observed as emperipolesis on imprint cytology. Its utility in identifying thymic cel ls in aspiration cytology needs to be investigated.