Cytology and flow cytometry to identify ectopic thymic tissue masquerading as a thyroid nodule in two children.

Background: Clinically unapparent thyroid nodules in children pose a significant problem in differential diagnosis and management. Ectopic thymic tissue in the thyroid gland is rare, but may masquerade as a thyroid nodule. This paper demonstrates the utility of flow cytometry as an adjunct to cytology by fine needle aspiration in diagnosing ectopic thymic tissue in the thyroid gland. Summary: By demonstration of T lymphocytes maturing along two cell lineages and the absence of markers for malignant lesions, fine-needle aspiration, cytology, and flow cytometry were used to identify ectopic thymic tissue masquerading as a thyroid nodule in two children. Conclusion: Use of this technique prevented surgical intervention that otherwise would have been necessary to obtain an accurate diagnosis of these thyroid nodules.