Although the American Thyroid Association's 2009 consensus statement on central neck dissection for papillary thyroid cancer (PTC) (Thyroid 2009;11:1153-1158) clarified the issue of unilateral versus ipsilateral procedures, debate continues over the use of prophylactic dissection in patients without visible thyroid nodules.
“Previously it was assumed that a surgeon did both sides, but now it is split into unilateral and bilateral dissection,” said David L. Steward, MD, Professor of Otolaryngology-Head and Neck Surgery, Director of the Parathyroid/Thyroid Surgery Program at the University of Cincinnati Medical Center, and a member of the Association's working group that developed the 2009 consensus statement.
“The other issue, which remains controversial, is whether to perform prophylactic surgery if a patient has no detectable nodes.”
He said the ATA has no plans to revisit the statement in the foreseeable future, which he described as a “clarification and one redefinition” of central neck dissection, and so the debate over prophylactic central neck dissection (CND) is therefore expected to continue. Even so, there are signs that more and more surgeons are performing such procedures.
The concept of therapeutic central neck dissection implies that nodal metastasis is apparent preoperatively or intraoperatively, or by imaging, he explained.
A prophylactic/elective central compartment dissection implies that nodal metastasis is not detected clinically or by imaging. Lymph node “plucking” or “berry picking” implies removal only of the clinically involved nodes rather than a complete nodal group within the compartment, and is not recommended under the guidelines, he said.
According to the guidelines, central neck dissection at a minimum should consist of removal of the prelaryngeal, pretracheal, and paratracheal lymph nodes.
“The feedback on the consensus statement was generally positive and widely accepted and adopted by surgeons,” Steward said.
Michael W. Yeh, MD, Director of the Endocrine Surgery Unit at UCLA, explained that several factors are involved in the decision to perform prophylactic central neck dissection.
“The rate of PTC has tripled over the past three decades. However, survival rates remain excellent. In fact, we don't worry that much about five- or 10-year mortality in most cases, so we have the luxury of considering secondary outcome measures such as recurrence rates, biomarker levels, and quality of life after treatment. This is where the debate centers.”
The five-year survival rates for patients with papillary thyroid cancer are now 100 percent for those with Stages I and II disease, 93 percent for Stage III, and 51 percent for Stage IV cancers. Whether or not to perform prophylactic central neck dissection comes down to a matter of risk versus benefit, Yeh said.
“The American Thyroid Association has issued two sets of management guidelines for thyroid nodules and differentiated thyroid cancer. The original document was published in 2006 and the revision in 2009. With respect to CND, only a minor change in wording occurred between the first and second set of guidelines: In 2006, it was stated that ‘routine central-compartment (level VI) neck dissection should be considered for patients with papillary thyroid carcinoma.’ This was softened in 2009 to ‘prophylactic central-compartment neck dissection (ipsilateral or bilateral) may be performed in patients with papillary thyroid carcinoma.’”
Prophylactic ipsilateral CND reduces the need for reoperations down the line, and often the reassurance of undetectable stimulated thyroglobulin (Tg) levels, but it carries the inconvenience of increased rates of temporary hypoparathyroidism, he continued.
“Many clinicians perceive this trade-off to be in the patient's favor, especially because surveillance is often simplified. In contrast, the risk-benefit profile of bilateral prophylactic CND is unfavorable as the high price of permanent hypoparathyroidism is not counterbalanced by any measurable oncologic gains.”
Recent literature indicates that ipsilateral prophylactic CND may be beneficial only when performed by an expert surgeon, Yeh said.
“If it is to be performed at all, prophylactic CND should be performed ipsilaterally only, and only by an expert. CND should not be performed by the occasional thyroid surgeon. The line between risk and benefit is razor-thin—if complication rates from CND rise more than a few percentage points, then it is no longer worthwhile.”
Importance of Compartment-Oriented Lymph Node Dissection
He emphasized the importance of compartment-oriented lymph node dissection: “The finding of one positive node in a given compartment of the neck is an indication for surgical clearance of all nodes within that compartment. It is rare for just one node in a compartment to be affected—usually it's several. Clearing the compartment reduces the likelihood that further surgery in the same area will be required later.”
In stark contrast to the situation for most other cancer types, the presence of papillary thyroid cancer within lymph nodes does not necessarily correlate with a poor prognosis, he said. “It is known that up to 70 percent of patients with PTC have positive lymph nodes if you look microscopically at the nodes. However, only a small fraction of these lymph node metastases end up being clinically significant. In the remainder, microscopic lymph node metastases seem to remain quiescent.
“The current challenge is that we are unable to predict which patients will end up having clinically significant lymph node recurrences. So we are left with a choice: either to treat everyone aggressively by performing routine prophylactic CND, or to leave out prophylactic CND and commit to re-operating on the small fraction of patients who will show up later with central neck lymph node recurrences.”
The risk of re-operation plays a part in his own decisions, Yeh explained. “I personally perform CND, because if a patient has a recurrence then I have to re-operate, and this means additional risks. Complications are two to three times more common in the re-operative setting. So I think it's worth it to pay a small price upfront by adding prophylactic CND to initial surgery, with the payout being realized in the avoidance of a high-risk re-operations.”
The counter-argument, though, he noted, is that the costs and risks of prophylactic CND are imposed on the entire population of patients with PTC.
Audience Poll at Association of Endocrine Surgeons Annual Meeting
Yeh noted that at the Association of Endocrine Surgeons Annual Meeting in April, the audience was informally polled on CND: “This was around 300 of the best endocrine surgeons in the world, and it was clear that more of them are now performing it. Among experts there is clearly an increasing trend in this direction. I was surprised at how many. Ten years ago it was around 10 percent, but today it is around 50 percent—and that's a trend.”
Recent Research Suggesting Role for Prophylactic CND
Several new studies lend weight to the argument in favor of prophylactic central neck dissection.
In one, researchers at Curie Institute in Paris reported that among 603 patients who were preoperatively categorized as node-negative and underwent prophylactic bilateral lymph node dissection, 23 percent had lymph node metastases, 19 percent of which were in the central compartment and eight percent were in the lateral compartment opposite the tumor. The findings are now available online ahead of print in World Journal of Surgery (Ducoudray R et al: DOI 10.1007/s00268-013-2020-y).
The study showed that hyperthyroidism and extrathyroidal invasion were significantly associated with cervical lymph node metastasis, and localization of the tumor in the upper third of the thyroid lobe and metastatic cervical lymph node in the central compartment were both independent risk factors for lateral metastasis.
Over a 4.3-year follow-up period, there were 23 recurrences, including five in the central compartment and two percent in the node-negative patients, five percent in the patients in which the cancer was limited to the central compartment, and 22 percent among patients where it had spread.
Another study, by researchers in China, examined the risks and benefits of prophylactic CND in 188 patients who underwent total thyroidectomy. The findings, published online on April 20 in Clinical and Translational Oncology (Wang et al: 10.1007/s12094-013-1038-9), showed node metastases in 44 percent of patients, with tumor size an independent positive predictor of lymph node metastasis.
Gender, age, tumor multifocality, tumor location, and capsular infiltration, however, were not. Postoperative complications occurred in 5.3 percent of patients, including 4.8 percent who developed temporary hypocalcemia, but there were no permanent cases.
Temporary laryngeal nerve injury occurred in just 0.5 percent of patients, while no permanent nerve injuries occurred, leading the researchers to recommend that all patients undergo prophylactic CND.
“With practice,” the researchers concluded, “the incidence of complications can be almost completely eliminated, while reducing tumor recurrence and mortality while promoting follow-up treatment.”