A 43-year-old woman presented with a mass in her left axilla, which was surgically excised. Histologically, the tissue was a reactive lymph node with adjacent thyroid follicular tissue. The differential diagnosis included benign
ectopic thyroid versus metastatic well-differentiated follicular-derived
thyroid carcinoma. Because of the possibility of
carcinoma, the patient underwent a diagnostic total
thyroidectomy. The thyroid was grossly normal with no histologic evidence of
malignancy. Post-operatively, the patient underwent a whole body 131I scan. Aside from an expected residual uptake in the thyroid bed region, there was no extrathyroidal uptake to suggest additional
ectopic thyroid tissue or metastatic disease. At the time of this scan, her
thyrotropin (TSH) was 92.8 microU/mL,
thyroglobulin was less than 0.3 ng/mL, and
thyroglobulin antibody was less than 3 IU/mL. Abnormalities in the embryologic development and migration of the thyroid gland can result in
ectopic thyroid tissue. The most frequent locations are along the midline from the base of the tongue to the mediastinum. Only rare case reports exist of
ectopic thyroid in other locations, including the chest (heart, trachea), abdomen (liver, gallbladder, pancreas), and pelvis (vagina). This case represents the first description of thyroid tissue in the axilla with a histologically benign thyroid gland.