Papillary Thyroid Cancer: Keys to a Successful Operation

For more than five decades, differentiated thyroid carcinoma — of which papillary thyroid carcinoma (PTC) represents more than 90 percent — has been recognized as one of the least life-threatening malignancies. Although this outcome is usually great news, it has led most investigators to abandon any hopes of developing prospective studies for the disease using disease-related death as an end point. Interest and investigation of PTC and the proliferation of management guidelines, however, have never been more intense than right now. How can these seemingly conflicting statements be reconciled?

Clive S. Grant, M.D. of the Department of Surgery at Mayo Clinic in Minnesota, says, "From a surgical perspective, between the 1980s and the turn of the century, the focus of treatment centered on the extent of thyroidectomy." Except for very small PTCs, which could be treated with unilateral lobectomy, total and near-total thyroidectomies were demonstrated to be equivalent and the preferred options.

Emerging as the hot new debate was the appropriate extent of associated lymph node dissection. Previously, lymph node metastases (LNMs) attracted only modest attention for several reasons. Large retrospective studies have consistently failed to identify LNMs as an important prognostic factor; the nodes seem rarely to either progress to or even indicate an in-creased risk of disease-related death. Former guidelines suggested excision of preoperatively or intraoperatively discovered palpable LNMs.

Since the turn of the millennium, however, three technological advances have driven profound changes in the overall management of PTC:

• Introduction and refinement of high-resolution cervical ultrasonography
• Use of recombinant human thyrotropin (TSH)
• Value and interpretation of serum thyroglobulin.

The increasing use of these three tools by endocrinologists has uncovered the frequent reality that LNMs may persist or recur postoperatively, and attempts to ablate them with radioactive iodine treatment are often an unreliable solution. Dr. Grant adds, "The whole mindset of treatment has shifted from death (a true rarity) to recurrence (an all-too-frequent event). The changes can be categorized into preoperative, intraoperative, and postoperative phases."

Preoperative Phase

Dr. Grant explains, "To discover LNMs that are macroscopic but not palpable either preoperatively or intraoperatively, we adopted the routine use of preoperative ultrasound when the result of the fine-needle aspiration of a thyroid nodule was either positive or suspicious for PTC. The locations of abnormal-appearing lymph nodes are recorded on a map, which is extremely helpful to the surgeon in planning the extent of lymphadenectomy necessary in conjunction with the thyroidectomy.

Of 551 patients undergoing initial operation from 1999 to 2004 at Mayo Clinic, 70 (12.7 percent) had nonpalpable nodes detected in the lateral compartment, whereas only 10 (1.8 percent) had similar nodes identified in the central compartment. Even 40 percent of those patients with palpable abnormal lymph nodes preoperatively benefitted from preoperative ultrasound that altered the operation.

Ultrasound Lymph Node map

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Intraoperative Phase

Dr. Grant adds, "Nearly 50 percent of our patients undergoing initial thyroidectomy for PTC have associated LNMs in the central compartment (compartment 6), yet preoperative ultrasound is unreliable in identifying these nodes (obscured by the presence of the thyroid gland). Therefore, we have added central compartment lymphadenectomy to the thyroidectomy as the standard operation for PTC. Many of these nodes have proved to be small and would have been potentially overlooked as normal intraoperatively but contain disease histologically. Many times, they may be located adjacent to the recurrent laryngeal nerves, which require full exposure and careful dissection in all PTC patients."

"Because the high internal jugular lymph nodes (level II) are infrequently involved with PTC and to dissect them requires significant extension of the neck dissection incision, we adopted levels III, IV, and the anterior portion of level V as our standard lateral compartment dissection (so-called modified radical neck dissection). Level II nodes are included in the dissection if palpable or indicated by preoperative ultrasound," says Dr. Grant. "Reliance on the results of ultrasound not only for the presence but also the extent of abnormal lymph nodes requires highly skilled, dedicated, and intellectually committed ultrasonographers. Fortunately, even with the extent of lymph node dissection in the central neck, complications of hypoparathyroidism and recurrent laryngeal nerve damage remain rare."

Lymph node compartments

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Postoperative Phase

Surveillance for disease recurrence has become increasingly intense, incorporating scheduled, routine testing for TSH-stimulated thyroglobulin levels and cervical ultrasonography. With a thyroglobulin level of 2 mcg/L considered the threshold for further imaging investigations for PTC, endocrinologists are discovering recurrent PTC LNMs even smaller than 1 cm. This small size mandates careful preoperative imaging and thorough intraoperative surgical excision of all PTC.

Dr. Grant concludes, "Using this surgical approach in 421 patients who received operations at Mayo Clinic from 1999 to 2006, with a median follow-up of 3.3 years, recurrence has been prevented in 96 percent of patients, where the extent of disease was accurately defined and potentially curable by neck surgery. Ultrasound had a false-negative rate of only 4 percent, and both permanent hypoparathyroidism and recurrent laryngeal damage occurred in less than 1 percent."