Parasitic thyroid nodules in patient with nontoxic multinodular goiter: a case report

INTRODUCTION: The presence of benign thyroid tissue that is located on the side of the neck is extremely rare and not related to the development of the thyroid, and it is difficult to differentiate it from thyroid carcinoma metastasis. The parasitic thyroid nodule occurs when thyroid tissue located in the lateral neck has no relationship or association with the lymph nodes, and may be defined as a thyroid nodule entirely separate from the thyroid or attached to it by a narrow pedicle, presenting the same histology and in the same facial plane as the thyroid, and should not be associated with lymph nodes. CASE PRESENTATION: A 40-year-old Brazilian man without significant past medical history presented with a large volume multinodular thyroid goiter that caused deformity and symptoms suggestive of cervical spine compression. He underwent a total thyroidectomy. His thyroid function was normal. Ultrasonography showed a heterogeneous thyroid nodule measuring 3.7cm to the right from midline and 3.3cm to the left from midline that was associated with two nodules in the left submandibular area measuring 1.43cm and 1.52cm. Fine needle aspiration confirmed the benign nature of the gland and thyroid tissue etiology of the two submandibular nodules, located in level II of the neck. Since the ectopic thyroid tissue in his lateral neck was suggestive of metastasis of occult primary thyroid carcinoma, the patient underwent a total thyroidectomy plus a left modified radical neck dissection with preservation of level I. The diagnosis of multinodular goiter associated with two parasitic thyroid nodules was confirmed by immunohistochemistry. CONCLUSIONS: We conclude that the parasitic thyroid nodule should be included in the differential diagnosis of lateral neck masses. The diagnosis and differentiation of these nodules from metastatic adenopathies of differentiated thyroid carcinoma has important therapeutic and prognostic implications, and can lead to avoidance of unnecessary surgeries.