Medullary Thyroid Cancer by Tracy S. Wang & Douglas B. Evans

Author:Tracy S. Wang & Douglas B. Evans
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Extent of Lymphadenectomy

The majority of studies on patterns of lymph node metastasis in MTC have included both hereditary and nonhereditary patients. Although bilateral tumors are more common in hereditary MTC patients, the pattern and frequency of lymph node metastases appear to be similar in both groups [31]. When lymph node metastases are clinically evident either on preoperative neck US or intraoperatively, a compartment-oriented lymph node dissection should always be performed. Prior to initial surgery, FNA biopsy of sonographically concerning level VI lymph nodes is not necessary, but FNA biopsy may be helpful to confirm lateral compartment (levels II–V) metastatic disease. Since MTC is commonly located at the central to upper lobes, the upper third of the lateral compartment (levels IIB and III) is more commonly involved [32]. Lateral compartment lymph node metastasis (LLNM) can be found without central compartment lymph node metastasis (CLNM), or so-called skip metastasis, in up to 10 % of MTC patients [32]. Thus, careful preoperative US assessment of all cervical lymph node basins is warranted.

In the absence of clinically evident lymph node involvement, serum calcitonin levels can be used to guide extent of concurrent lymphadenectomy. The likelihood of lymph node disease is exceedingly low when preoperative serum calcitonin levels are <40 pg/mL and lymphadenectomy may not be needed [12, 33]. However, for many RET mutation carriers with a preoperative diagnosis of MTC, determined either biochemically or by FNA biopsy, the preoperative serum calcitonin is likely ≥40 pg/mL, and at a minimum, concurrent central compartment lymph node dissection is indicated. In a systematic evaluation of 300 patients with MTC, the likelihood of central compartment lymph node metastases when the basal serum calcitonin level was <50 pg/mL was 9 % and increased with rising basal serum calcitonin levels [12]. In 73 hereditary and nonhereditary MTC patients who presented with a palpable nodule, 79 % had central compartment lymph node metastases [34]. Furthermore, intraoperative assessment by an experienced surgeon identified positive lymph node in only 64 % of patients with positive lymph nodes. Thus, a compartment-oriented central compartment lymph node dissection is recommended for all patients with clinically evident MTC.

When lateral compartment neck disease is not evident on preoperative imaging, LLNM may still be likely especially if CLNM are present. In a study by Machens et al., when even one central compartment lymph node was positive for metastatic MTC, the likelihood of LLNM was 71 % [32]. However, unless clinically apparent, CLNM is often diagnosed on histology. It remains controversial if prophylactic dissection of the ipsilateral lateral compartment should be routinely performed for all patients who have a central compartment neck dissection, or if extent of lateral neck dissection should be guided by ultrasound findings [2]. When basal serum calcitonin levels are ≥200 pg/mL, contralateral lateral compartment neck dissection can also be considered, even if imaging is negative [2, 12]. Preoperative CEA levels can also be useful to predict volume of disease.

Following surgery, the likelihood of biochemical cure is ~30 % in patients with node-positive disease and this is inversely proportional to the number of involved lymph nodes [35].

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