Thyrothymic thyroid rests: incidence and relationship to the thyroid gland.

Background: Rests of thyroid tissue within the thyrothymic area are relatively common and might be of clinical importance. The purpose of this study is to define the incidence and anatomy of thyroid tissue located in the line of the thyrothymic ligament, referred to here as "rests."

Study Design: Prospective descriptive intraoperative evaluation of 100 consecutive thyroid or parathyroid procedures was undertaken to identify the incidence and anatomical location of thyrothymic thyroid rests. Photographs and histologic confirmation of the thyroid remnants were obtained.

Results: One hundred eighty sides of the thyroid gland are examined in 100 consecutive patients. Thyroid rests in the thyrothymic area were found in 53 patients, or on 83 separate sides of the thyroid (46%). In patients who had rests identified, 30 (57%) had bilateral rests, with 16 (30%) only on the right, and 7 (13%) only on the left. Eighty percent of identified rests were still attached to the thyroid proper by a pedicle of thyroid tissue but 20% were entirely separate. Most rests were small, with 88% being less than 1 cm in diameter.

Conclusion: Rests of thyroid tissue within the thyrothymic area, either as entirely separate nodules or as prolongations from the thyroid lobe, are relatively common and might be of clinical importance during thyroid or parathyroid surgery.