Papillary thyroid carcinoma (PTC) is known to have an excellent prognosis with 10-year survival rates exceeding 90% (1). In the case of papillary thyroid microcarcinoma, the disease specific mortality rate has been reported to be less than 1%, with locoregional recurrence rates of 2%–6% (23). As a result, the extent of thyroid surgery and lymphadenectomy has become less aggressive. Moreover, since the 2015 American Thyroid Association (ATA) guidelines, the incidence of thyroid lobectomy has been increasing in patients with PTC up to 4 cm, despite continuing controversy about the appropriate extent of surgery (4).

Completion thyroidectomy (CT) is a procedure to remove remnant thyroid after thyroid surgery, and it is known to have a higher complication rate compared to primary surgery due to adhesion and fibrosis (56). Immediate postoperative CT can be performed in patients who were diagnosed with cancer postoperatively, who have remaining thyroid cancer, or who have to undergo radioactive iodine treatment due to aggressive pathological features. During the follow-up period after thyroid lobectomy, CT can be performed in cases of recurrences, contralateral thyroid cancer, or symptomatic benign thyroid disease. In these cases, it is challenging for surgeons to predict the timing and complications of CT.

In this study, we analyzed the patients who underwent CT during the follow-up period after thyroid lobectomy for PTC and evaluated the causes, timing, and safety of CT.

The 2015 ATA guidelines recommended thyroid lobectomy in low-risk patients with tumors up to 4 cm and clinically negative LN (4). Several studies have demonstrated that thyroid lobectomy and total thyroidectomy had similar overall survival rates in patients with 1–4 cm-sized PTCs (789). Recurrence rates during the follow-up period after lobectomy are reported to be very low and to have no effect on the survival rate if properly treated (7910). For these reasons, the preferences of surgeons regarding the necessary extent of thyroidectomy has shifted from total thyroidectomy to lobectomy, despite continuing controversy.

CT is usually recommended for patients who would have been treated by total thyroidectomy if they had been diagnosed with malignancy before surgery or those who must undergo radioactive ablation treatment. According to the National Comprehensive Cancer Network (NCCN; http://www.nccn.org), postoperative CT is recommended in cases of tumor size >4 cm, positive resection margin, macroscopic nodal metastasis (>5 mm) or multiple LN metastasis (the number of LNs >5), macroscopic multifocal disease (>1 cm), or vascular invasion on the pathologic report. In these cases, most completion thyroidectomies are conducted within 6 months by the same surgeon and the complications are predictable. In this study cohort, the number of cases of immediate postoperative CT was 4 for PTC and 4 for follicular thyroid cancer during the study period. In our institution, intraoperative frozen section analysis was conducted for suspicious LNs, and when metastasis was confirmed, the extent of thyroidectomy was changed to total thyroidectomy during surgery. Thus, the incidence of immediate postoperative CT was relatively low.

Despite an excellent prognosis, many patients with PTC are anxious and fearful of recurrence (11). Although thyroid lobectomy has advantages in terms of avoiding lifelong thyroid hormone replacement therapy, many patients worry about remnant thyroid tissue. Recent studies reported locoregional recurrence rates of less than 1%–4% and a CT rate of less than 10% after thyroid lobectomy (912). Typically, recurrence of PTC occurs within first 3–4 years, and most of the cases are considered disease persistence with possible enlargement rather than true recurrence (1314). In our study, half of the completion thyroidectomies were conducted within 4 years in both the recur CT and non-recur CT groups, with the other half occurring anytime after 4 years. We analyzed the clinicopathologic characteristics of primary surgery based on median timing, 4 year. Multiple PTCs and older age were correlated with CT within 4 years. It is well known that PTC can have multiplicity, and the rate of occult carcinoma in contralateral lobe is reported at 13%–56% (1516). A new primary lesion in the contralateral lobe is likely to be a persistent tumor in patients who underwent CT within 4 years. The odds ratio of 0.921 for the age is not impressive. The factor of age seems to be correlated with timing due to the differences in remaining lifespan between the patients underwent CT within and after 4 years.

Reoperation is considered to have a higher risk of postoperative complications. Tissue inflammation, adhesions, and scar tissue formation after primary surgery make it difficult to distinguish normal tissue (61718). This leads to an increased risk of recurrent laryngeal nerve or parathyroid gland injury during tissue dissection. However, in the case of CT after lobectomy, recurrent laryngeal nerve and parathyroid glands are less affected by the previous surgery. Rafferty et al. (19) reported similar complication rates between CT and total thyroidectomy with incidences of temporary recurrent laryngeal nerve paresis of 2.0% and 3.3% and permanent hypoparathyroidism of 2.5% and 3.3% in completion and total thyroidectomy, respectively. Rudolph et al. (20) reported a significantly lower rate of permanent recurrent laryngeal nerve palsy and hypoparathyroidism during reoperation after thyroid lobectomy than after bilateral subtotal thyroidectomy (0.77% vs. 3.4% and 1.5% vs. 5.1%, respectively). In our institution, one patient complained of hoarseness after CT with MRND due to ipsilateral LN recurrence at 33 months after primary surgery, though the symptom returned to normal within several months. There was no recurrent laryngeal injury, though severe adhesion was reported. Temporary hypoparathyroidism was reported in 25.3% (16/63) of the patients in this study. In most cases, their symptoms improved within 6 months, and persistent hypoparathyroidism was observed in only 1.58% (1/63). One patient received CT with CCND due to contralateral PTC at 76 months after the primary surgery, and there was no evidence of parathyroid gland injury. One patient was re-admitted with wound swelling and pus-like discharge on the seventh postoperative day.

To reduce the complication rate of CT during the follow-up period after lobectomy, a clear understanding of the operative findings of the primary surgery and a thorough preoperative evaluation are very important. Surgeons must ascertain whether there was any recurrent laryngeal nerve or parathyroid gland injury or if any other events occurred at the time of primary surgery. In the absence of information about the primary surgery, it is necessary to evaluate vocal cord function and a neuro-monitoring device may also be helpful. Exact localization is also critical, especially in cases of operative site bed recurrence or ipsilateral LN recurrence. Ultrasound-guided skin marking or charcoal suspension tattoo localization may reduce the extent of dissection.

This study has limitations of retrospective study. Information about complications was obtained solely from the chart records, and the rates may have been somewhat underestimated owing to the possibility of complications that the patients did not report. However, the low number of complications in this report may help reduce patients' anxiety about reoperation.

In conclusion, along with the increased rate of thyroid lobectomy, the frequency of CT is expected to increase. CT is an unexpected event that may occur anytime during the patients' lifetime after lobectomy. However, it is no longer a challenging surgery and the postoperative complication rate is relatively low. Special attention should be paid during surgery.