Thyroid Tubercle of Zuckerkandl May Not Arise from the Ultimobranchial Body: Results from Histological Analysis.

Thyroid tubercle of Zuckerkandl (TZ) is a nodule arising from the posterolateral thyroid, considered to be a remnant of the ultimobranchial body (UB). Considering that C cells and solid cell nests also arise from the UB, we hypothesized that these would be present in the TZ. We examined the presence of C cells and solid cell nests in the TZ using the histological analyses of 21 patients with grade 2 or 3 TZs following Pelizzo's grading system. Out of 21 TZs, 19 (90.5%) were located in the right lobe of the thyroid. Microscopically, solid cell nests were found within the TZ in 1 case (4.8%), and within the main thyroid tissues in 3 cases (14.3%). Calcitonin-positive C cells were scattered within the TZ in 1 case (4.8%), and within the main thyroid tissue in 15 cases (71.4%). The distribution of C cells within the main thyroid tissue was denser than that within the TZ. The above-mentioned results indicated the lack of C cells and solid cell nests in the TZ. Although the TZ may have an embryological origin different from that of ordinary thyroid tissue, it is unlikely that the remnants of the UB are involved in the formation of the TZ.