Cytologic diagnosis of true thymic hyperplasia by combined radiologic imaging and aspiration cytology: a case report including flow cytometric analysis.

True thymic hyperplasia (TH) is an age-dependent increase in size and weight of the thymus gland, which by definition maintains a normal histologic architecture. TH can mimic other important diseases, including lymphofollicular hyperplasia, thymoma, lymphoma, and germ-cell tumors. Traditionally, separating these entities has required a formal surgical biopsy. Given that many of these conditions occur in children, this can be a traumatic experience for both the patient and family members. Fine-needle aspiration biopsy has the distinct advantage of being able to obtain diagnostic material without requiring general anesthesia. We are aware of only one previously reported case of an enlarged thymus being subjected to aspiration cytology. We therefore present a case of thymic hyperplasia in a 5-mo-old child diagnosed by combined radiologic and cytologic parameters, including flow cytometric analysis.