Preoperative Radiographic Mapping of Nodal Disease for Papillary Thyroid Carcinoma

Macroscopically Positive Versus Microscopically Positive Metastasis

An important issue in the discussion of PTC nodal metastasis is the segregation of LNs into macrometastasis (or clinically apparent metastasis) and micrometastasis. Studies of patients with PTC demonstrate that macroscopic cervical nodal metastasis (as determined by detection through preoperative physical examination [PE], ultrasound [US], or intraoperative detection) will occur in 21% to 35% of patients at presentation. Microscopically positive nodes are far more prevalent, occurring in 23% to 81% of patients with clinically negative preoperative nodal assessments on whom prophylactic LN dissection is performed. Therapeutic nodal dissections target macroscopically positive nodes, whereas prophylactic neck dissections target normal or microscopically positive LNs.

Macroscopic LN metastases are associated with increased rates of recurrence-free survival (RFS), unlike micrometastases. In fact, several studies have shown that patients with microscopically positive nodes have recurrence rates similar to those of patients with pathologically negative nodes. Although some authors have shown an intermediate outcome in patients with microscopic LNs, radiographically identified macroscopic nodes in the lateral neck have been shown to be associated with significantly lower RFS rates compared with pathologically positive and US-negative nodes (i.e., microscopically positive nodes).

Therefore not all nodes are created equal in terms of actual prognostic downside; it is only macroscopically identified nodes (i.e., clinically apparent nodes) that require detection and resection.

Importance of Radiographic Detection of Macroscopically Positive Nodes PrEoperatively

Nodal surgery for macroscopically positive nodes is required in approximately one third of patients who have PTC. If doctors do not recognize this task preoperatively, then persistence or recurrence of nodal disease is certain. Revision surgery is recognized to be more difficult than primary surgery due to scarring from the initial surgery. Therefore to save the patient from additional surgery and increased risk, removal of all macroscopic metastatic disease at the time of the initial surgery is desired. A surgeon cannot ascertain involvement of LNs from tumor characteristics alone, even though extrathyroidal extension and tumor size have shown correlation with positive macroscopic LNs. Therefore it is essential to use high resolution radiographic analysis before surgery to detect macroscopically positive nodes to plan an operation appropriate for each patient’s individual disease extent.

Central Neck Nodes

Despite the high prevalence of cervical LN metastases, controversy exists regarding the extent of neck dissection needed for patients with PTC. Some surgeons perform prophylactic central neck dissection (pCND), but this additional surgery across all surgical settings will undoubtedly increase complications, such as hypoparathyroidism and recurrent laryngeal nerve injury. This procedure (pCND) harvests normal or at best microscopically positive nodes. In light of what we know about microscopically positive nodes as stated earlier, it is not surprising that pCND has been shown to have no effect on survival or recurrence.

Intraoperative palpation to detect nodal disease also demonstrates a low degree of sensitivity and reliability. Studies have shown experienced surgeons can identify fewer than 50% of grossly positive nodes through intraoperative palpation.

Societies worldwide have various recommendations for central neck dissection in thyroid cancer surgery. The 2015 guidelines from the American Thyroid Association recommend a therapeutic central compartment neck dissection in patients with clinically involved central nodes and a pCND in those with advanced papillary tumors or clinically involved lateral nodes. The National Comprehensive Cancer Network’s expert panel and the European Society of Endocrine Surgeons recommend pCND in advanced or high-risk tumors, especially at specialized centers. The British Thyroid Association states that the benefit of pCND for high-risk patients is unclear; and recommends personalized care on a case by case basis with an understanding of the expertise of the given surgical team. In contrast, the Japanese Society of Thyroid Surgeons and the Japanese Association of Endocrine Surgeons recommend routine pCND; the two groups state that it is helpful in preventing LN recurrence. Although opinions differ on prophylactic neck dissection, therapeutic neck dissection is recommended for clinically involved central nodes. Therefore objective radiographic data obtained preoperatively are required before surgery.