Janice L. Pasieka
What to do with the lymph nodes in well-differentiated thyroid cancer
Recently, the management of the lymph node compartments in well-differentiated thyroid cancer (WDTC) has been the focus of much debate among the surgeons and endocrinologists dealing with this disease. Why has there been so much recent ‘press’ on this topic? Much of this has to do with the changing paradigm in the definition of thyroid cancer recurrence. Until a decade ago the identification of recurrence in WDTC relied on physical examination and/or the demonstration of disease on follow-up radioactive I131 scans. This has changed with the advent of high-resolution ultrasounds and the measurement of stimulated thyroglobulin (Tg) levels. These technological advances have allowed for the identification of disease that was too small to detect by physical examination and I131 scanning. As such, the definition of persistent and recurrent disease has changed in recent years. Because of this, endocrinologists, medical oncologists and surgeons have questioned whether more extensive surgical removal of the disease at the first operation would benefit this patient population—hence the development of prophylactic central neck dissections (pCLNDs).
In this monograph, Pathak and Nason have described their approaches to both the central and lateral neck compartments in WDTC. The American Thyroid Association (ATA) set out to provide guidance on the issue of pCLND, yet recognized early that uniformity in definitions was needed to interpret the current literature. Carty et al. defined the central neck and introduced definitions for ipsilateral and bilateral level VI dissections . It is important that surgeons operating for thyroid cancer are familiar with these standardized definitions. Level VI includes the tissue between the carotid sheaths from the hyoid bone to the innominate artery. This includes the pyramidal lobe, forgotten by many, the anterior peritracheal tissue and the tissue deep in the neck in which the inferior parathyroid gland and recurrent laryngeal nerve (RLN) lie. It is because of the close proximity of the RLN to the parathyroid glands that pCLND should not be taken lightly [2, 3]. Although risk to the RLN appears to be similar to that from total thyroidectomy alone, hypoparathyroidism is increased, especially when bilateral pCLNDs are performed [2, 3]. The clinical benefit of removing clinically negative nodes (cN0) from this compartment has been discussed extensively in the literature. Most authors would agree that to date no survival benefit is seen in patients undergoing a pCLND for WDTC . Some have argued that CLND decreases postoperative serum thyroglobulin (Tg) levels, thus decreasing recurrence/persistence rates . The oncological principle of removing the draining lymph node basin for most cancers is to stage the patient accurately, and as such, influence postoperative therapy. Forty per cent of patients with cN0 disease were up-staged as a result of the histological findings on pCLND. Not surprising, given the high incidence of positive lymph nodes in WDTC. However, in centres that provide selective I131 ablative therapy, pCLND has led to an increased utilization of I131 therapy in 33 % of WDTC patients . Many centres utilize a more selective use of I131 therapy in low-risk patients because of the lack of survival benefit seen with its use . Thus, for the individual surgeon dealing with WDTC, the need for pCLND must be individualized to that surgeon and their referral cancer centre. First, the surgeon must know his/her rate of RLN injury and hypoparathyroidism with CLND. Second, the surgeon has to understand how the additional information from the central lymph nodes will be utilized. If their centre routinely gives I131 to all patients regardless of the risk status, then pCLND may be of little benefit. If the centre selectively gives therapy to all N1 disease, providing the additional staging information gained from the pCLND may be of some benefit. Yet clinically, most clinicians recognize that there are varying degrees of magnitude in the risk for recurrence for N1 disease. The upstaging of low-risk patients with small-volume nodal disease conveys a much smaller risk of recurrence than those with large-volume disease. Randolph et al. have recently proposed an N1 stratification for the use of I131 therapy . Their document provides a rational approach to the question of how to utilize the information provided from a CLND.
A prospective, randomized controlled trial of pCLND in WDTC would help clarify this issue for the surgeons. However, given the low rates of both structural recurrence and morbidity after surgery for cN0 disease, prohibitively large sample sizes would be required for sufficient statistical power to demonstrate significant differences in outcomes . Biochemical molecular tumour markers are gaining wider use in clinical practice and in time, hopefully, will provide more specific information on which surgical decision-making can be based [4, 10].
Clinically positive lymph nodes warrant a compartmental dissection, as outlined by Pathak and Nason in this monograph. The utilization of preoperative lymph node mapping with ultrasound has become the standard of care in most North American centres. Recent changes in the ATA guidelines for medullary thyroid cancer have moved from routine lateral neck dissections to selected dissections of the lateral compartments on the basis of lymph node mapping . Although this approach relies on the sensitivity of thyroid ultrasonography, surgeons, endocrinologists, along with radiologists are becoming more skilled with this adjunct in the clinical evaluation of the thyroid and its regional lymph node basins. Most clinicians have expanded the role of ultrasound lymph node mapping with fine-needle aspiration confirmation to WDTC. This approach helps prepare both the patient and the surgeon preoperatively.
Lymph node metastases are common in WDTC. Clinically positive lymph nodes require a compartment dissection. The surgical approach to the regional nodal basin in cN0 disease is currently under debate. Risk versus benefit for the patient should continue to guide the surgeon when treating WDTC.
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