Thymoma mimicking thyroid papillary carcinoma: another pitfall in fine-needle aspiration

A six-year-old boy with a suspicious thyroid nodule: intrathyroidal thymic tissue

BACKGROUND

Ectopic intrathyroidal thymus tissue that forms mass lesions as a consequence of aberrant thymic migration during embryogenesis is rarely reported in the literature.

METHODS

We present the case of a 6-year-old boy with a right thyroid nodule and bilateral cervical lymph nodes. Thyroid hormone, antibodies, and routine chemistry tests were normal. Real-time thyroid ultrasound showed a right calcified nodule measuring 8 x 5 x 7 mm and multiple bilateral cervical lymph nodes. I131 scan showed mild decreased uptake in the right upper lobe. On fine-needle aspiration biopsy we discovered an atypical lymphoid proliferation that was suspicious, although not diagnostic, of a lymphoma. Immunostain for calcitonin was negative. Flow cytometry of the thyroid nodule aspirate demonstrated an abnormal polyclonal T cell population with dual expression of CD4 and CD8, and a subpopulation of cells that expressed TdT suggesting the possibility of lymphoblastic lymphoma. DNA analysis, as well as polymerase chain reaction for T cell and B cell gene rearrangement, did not demonstrate changes in the gene for the heavy chain of immunoglobulin of B cells and gamma chain of the T cell receptor. Lymph node aspirate showed unremarkable T and B lymphoid cells.

MAIN OUTCOMES

The diagnosis of ectopic intrathyroidal thymus was made after the operation.

CONCLUSION

Ectopic thymus tissue should be considered in the differential diagnosis of thyroid masses, especially in children.

[Thymoma. A retrospective study]

We review cases of thymic cell tumor treated between January 1991 and March 1998. Nineteen of the 23 cases studied involved thymoma. Eight (42%) were asymptomatic, 4 (21%) were associated with myasthenia gravis and 7 (37%) were symptomatic. The most common symptom was non-specific chest pain, reported by 4 (47%) patients with symptoms. Classifying the cases of thymoma by Masaoka's system, we found that 12 were cases of thymoma in stage I (63.2%), 4 in stage II (21.1%) and 3 in stage III (15.8%). No stage IV patients were treated. Treatment consisted of full exeresis of the tumor in 17 (89.5%) cases, partial resection in one case (5.2%) and biopsy of the tumor in one non-resectable, case. Adjuvant radiotherapy was applied in seven cases. Chemotherapy was not prescribed. With follow-up ranging from 9 to 96 months, half the patients survived 21 months after surgery. Among the surviving patients, mortality was nil at the end of the study. The results of microscopic, cytologic and blood analyses were of scarce value in differentiating between benign and malignant tumors, even though p53 and bcl2 antigen positivity and clinical stage have been related to poor prognosis in recent years.