https://orcid.org/0000-0003-1052-5348
Papillary thyroid carcinoma (PTC) is the most common histologic type of differentiated thyroid cancer and is considered to be a relatively indolent tumor from which death is rare. Recent advances in diagnostic modalities have facilitated the early detection and accurate diagnosis of PTC, especially for those with subclinical disease [Citation1]. Due to the good prognosis of PTC, there has been increasing interest in reducing surgical morbidity and patient discomfort by minimizing surgical complications.
The thyroid isthmus is the central part of the thyroid gland that lies directly anterior to the second to fourth tracheal rings and is covered by the strap muscles in the neck. Although only less than 10% of PTC is limited to the thyroid isthmus, it is known to have a higher incidence of multifocality and capsule invasions compared to lesions presenting in the thyroid lobes [Citation2].
There are no precise recommendations or guidelines for management of isthmic PTC, but there have been various discussions of the determination of optimal surgical extent [Citation2–4]. The benefits of total thyroidectomy are that it can treat multifocal occult tumors in bilateral thyroid lobes, radioactive iodine ablation can be used postoperatively, and thyroglobulin can be used as a monitoring tool during follow-up. However, injuries to the recurrent laryngeal nerve (RLN), superior laryngeal nerve, and parathyroid gland as well as the incidence of complications are known to be more likely than with other surgical methods. Conversely, in patients who underwent thyroid isthmusectomy, the incidence of hypothyroidism was less likely and there was less possibility of laryngeal nerve palsy and hypoparathyroidism. Hence, the commented study by Hanyang University [Citation5] investigates the clinical efficacy of thyroid isthmusectomy by evaluating the difference in surgical outcomes and prognosis according to the surgical procedures used in isthmic PTC. This retrospective study included 121 patients who were diagnosed with a solitary isthmus PTC without clinically suspected lymph node metastasis and gross extrathyroid extension. Total thyroidectomy, lobectomy with isthmusectomy, and isthmusectomy were performed in 70 (57.8%), 40 (33.1%), and 11 (9.1%) patients, respectively. Prophylactic central neck dissection (pCND) was performed in 104 (86%) patients, and 24 patients (34.3%), 11 patients (27.5%), and 4 patients (36.4%) showed occult central cervical lymph node metastasis (pN1a) in the total thyroidectomy, lobectomy, and isthmusectomy groups, respectively. In a subgroup analysis, patients who underwent total thyroidectomy or lobectomy showed higher postoperative complication rates than those who underwent isthmusectomy. However, there were no differences in recurrence rate or survival among the three groups. Therefore, the authors conclude that thyroid isthmusectomy might be effective in the surgical treatment of small single isthmic PTC, considering its low complication rates and acceptable oncologic outcomes.
The major strength of the commented study was their analysis and comparison of surgical outcomes and prognosis according to different surgical procedures. However, the study was limited by the non-randomized retrospective design, small sample size, and the short follow up period. Therefore, further prospective studies with a large sample size and long-term follow up are necessary. In addition, there are several concerns that need to be recognized. In this study, 10 of 11 (91%) patients in the isthmusectomy group underwent pCND and 4 patients showed occult central cervical lymph node metastasis. This finding suggests pCND should also be considered in patients who underwent isthmusectomy for management of solitary isthmic PTC.
A recent meta-analysis [Citation6] reported that patients with PTC who underwent pCND had significantly lower locoregional recurrence rates, but this was accompanied by numerous adverse effects compared with no pCND, including higher incidence rates of transient recurrent RLN injury (OR 2.03; 95% CI 1.32-3.13). Although there was no vocal cord paralysis reported in the isthmusectomy group in this commented study, there was a risk of RLN injury because the path of the RLN is included in the surgical field of pCND [Citation7].
Intraoperative neuromonitoring (IONM) has gained widespread acceptance as an adjuvant to visual RLN identification during thyroid surgery [Citation8–10]. The adoption of thyroidectomy isthmusectomy for management of solitary isthmus PTC is expected to reduce surgical morbidity. This procedure is usually performed through a small incision wound, and the application of IONM should be considered during the pCND because it could facilitate RLN mapping and aid in dissection, allowing for clear cut differentiation between neural versus non-neural tissues.
Appropriate surgical treatment of isthmus PTC remains controversial. Although the commented study provides excellent evidence that isthmusectomy could be an effective procedure in selected patients with low-risk isthmus PTC, patients have to be counseled about the potential long-term risk of recurrence due to the remaining occult carcinoma in the bilateral thyroid lobes. Future studies are needed to understand the long-term risk-benefit ratio of adopting thyroid isthmusectomy and routine pCND for isthmus PTC patients. Current clinical decisions might be made after a shared decision-making process between clinicians and patients.
Disclosure statement
The authors report no conflict of interest. This work was supported by the Kaohsiung Municipal Siaogang Hospital, Kaohsiung Medical University, Taiwan under Grant H-108-005.
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.
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