Parasitic thyroid nodule in a patient with Hashimoto's chronic thyroiditis

A case of parasitic thyroid nodule is presented. The patient was a non symptomatic 53-year-old white woman, on irregular course of L-thyroxine to treat hypothyroidism due to Hashimoto's thyroiditis. Without a history of thyroid trauma or surgery, she presented a 1.6 x 0.7 x 0.5cm right pre-laryngeal lymph node-like mass which, on ultrasonography, appeared distinct from the gland. TSH, thyroid peroxidase antibody and thyroglobulin antibody serum levels were elevated and T4-free level was normal. Thyroid and total body 99mTc isonitrile scintiscan showed a topic thyroid without radionuclide uptake in the nodule. Fine-needle aspiration of the nodule showed epithelial cells with nuclear atypia and oncocytic changes plus intense lymphoid infiltration and germinative center formation, simulating lymph node metastasis of papillary thyroid carcinoma. Conventional biopsy revealed a parasitic thyroid nodule with Hashimoto's chronic thyroiditis. Parasitic thyroid nodule must always be remembered so that unnecessary surgical assessment and undesirable sequels may be avoided.