More than just stuck in the middle: papillary thyroid cancer of the isthmus may present with aggressive features and nodal metasasis.

INTRODUCTION

Differentiated thyroid cancer is the most common endocrine malignancy and has an excellent 5-year survival rate after appropriate management. Current management guidelines state that thyroid lobectomy is adequate resection for papillary thyroid cancer (PTC) without preoperative evidence of high-risk features. However, the extent of surgery for PTC in the thyroid isthmus remains controversial, given the unclear lymphatic drainage and retrospective studies suggesting higher rates of lymphatic metastasis. The aim of this study was to examine the surgical management and outcomes of patients with isthmus PTC.

METHODS

A retrospective review was performed at two high-volume centers of 138 patients who underwent thyroidectomy between 2013 and 2021 with isthmus PTC on final pathology. Preoperative tumor characteristics, surgical pathology, and postoperative outcomes were compared.

RESULTS

There were 138 patients treated for isthmus PTC. Total thyroidectomy (TT) was most frequently performed (70.0 ​%), followed by lobectomy (TL, 17.1 ​%) and isthmusectomy (TI, 12.9 ​%). Among the 106 patients with Bethesda V/VI nodules, most underwent TT (75.5 ​%), followed by TL (13.2 ​%), and TI (11.3 ​%). Patients with Bethesda III/IV nodules most frequently had TI (44.4 ​%) or TL (44.4 ​%), then followed by TT (11.1 ​%). Patients who underwent TT more frequently had suspicious lymph nodes on preoperative imaging (n ​= ​30, n ​= ​1, n ​= ​0, p ​< ​0.001) and/or multiple nodules than TL and TI respectively (73.5 ​%, 70.8 ​%, 16.7 ​%, p ​< ​0.001). Of TT patients, 48 had central neck dissections (29 prophylactic and 19 therapeutic) and 20 had both therapeutic CND and lateral neck dissections. TT patients had larger median tumor size (1.5 ​cm; TL 1.1 ​cm; TI 1.0 ​cm; p ​= ​0.008). PTC variants were identified in 26.1 ​% of patients. Completion thyroidectomy was performed in 4 patients (TL, n ​= ​2; TI, n ​= ​2, p ​= ​0.41). Of 99 patients with lymph nodes sampled, 62 patients had metastatic lymph nodes (TT 58.2 ​%; TL, 16.7 ​%; TI: 11.1 ​%; p ​= ​0.02). At the last follow-up, 10 patients had persistent/recurrent disease (TT: 8, TI: 2, TL: 0). At one year, among patients who did not undergo TT, 10 patients required thyroid hormone replacement (TL: 56 ​%; TI: 10 ​%; p ​= ​0.018).

CONCLUSION

Isthmus PTC may present with high-risk pathologic variants and positive nodes in 2 out of 3 patients. TI may be an appropriate management strategy in small, low-risk tumors, with similar reoperation rates as TL and lower rates of needing thyroid hormone replacement.