Separate thyrothymic thyroid remnant; clinically crucial anatomic variation.

Purpose: The anatomical variations of the thyroid gland including separate thyroidal remnant at the thyrothymic area are of significance during thyroid surgery for "total" thyroidectomy, and for recurrent goitre. In the present study, we aimed to detect the separate rests of thyroidal tissue in the thyrothymic region.

Methods: The thyrothymic region was explored for identification, dissection, and excision of separate thyroidal remnants in 134 patients who underwent primary thyroid surgery. In this series, we studied the incidence and anatomical features of the thyrothymic remnant and its relation with other embryologic remnants.

Results: Overall, 222 sides of the thyroid were explored in this study. An entirely separate thyrothymic remnant of the thyroid was identified and excised in 8 of 134 patients (6%). Mean size of removed remnants was 36.4 mm (range, 29-45 mm) in diameter. The incidences of pyramidal lobe (PL) and Zuckerkandl's tubercle (ZT) were 71.6% and 59.7%, respectively. The thyrothymic remnant coexisted with PLs in 4 patients. Four patients had all 3 embryologic remnants: thyrothymic remnant, PLs, and ZTs.

Conclusion: An entirely separate thyroidal remnant at the thyrothymic area is not a rare variation. The considerably large size of a remnant may threaten the completeness of thyroidectomy and may result in recurrence if it is left behind after thyroid surgery. Awareness, identification, and excision of the separate remnant at the thyrothymic area and the other embryologic remnants are critical for ensuring completeness of thyroidectomy and preventing recurrences.