Frequency and predictive factors of malignancy in residual thyroid tissue and cervical lymph nodes after partial thyroidectomy for differentiated thyroid cancer.

Background: The extent of surgery in differentiated thyroid cancer (DTC) has been a controversial issue. Total thyroidectomy potentially carries a higher operative risk, whereas partial thyroidectomy has the risk of leaving significant residual malignancy. The aim of this study was to assess the frequency and potential predictive factors of malignancy in the residual thyroid tissue and the cervical lymph nodes (CLN) in patients with DTC who had partial thyroid surgery and subsequently underwent completion thyroidectomy and/or modified neck dissection. Age, gender, pressure symptoms, duration of symptoms, size of the original tumor, tumor multifocality, perithyroidal tumor extension, soft tissue invasion, and serum thyroglobulin (Tg) level after first surgery were analyzed as potential predictive factors for the presence of malignancy in the thyroid remnant and the CLN.

Methods: We retrospectively reviewed the medical and pathologic data of 101 cases of DTC; 97 had papillary and 4 had follicular thyroid cancer. On the initial surgery, the median tumor size was 2.5 cm (range, 0.5 to 8.5 cm). Tumor multifocality occurred in 28 cases, perithyroidal tumor extension in 26 cases, and soft tissue invasion in 9 cases. Completion thyroidectomy was performed in 100 cases and modified neck dissection in 90 cases.

Results: On completion neck surgery, 39 patients had evidence of malignancy in the residual thyroid tissue and 36 patients in the CLN. In 23 (22.7%) cases, malignancy was present in both CLN and residual thyroid tissue. Only tumor multifocality and Tg level greater than 20 ng/mL after first surgery were predictive of the presence of malignancy in the thyroid remnant, whereas age older than 40 years, soft tissue invasion, perithyroidal tumor extension, and Tg level greater than 20 ng/mL were predictive of malignancy in CLN.

Conclusions: Residual malignancy is common after partial thyroid surgery for DTC. Tumor multifocality and Tg level may be predictive of its presence in residual thyroid tissue. Age, perithyroidal tumor extension, soft tissue invasion, and Tg level are predictive of the presence of lymph node metastases.