Clinical features and imaging examination assessment of cervical lymph nodes for thyroid carcinoma

The incidence of cervical LNM reaches 40–90% in PTC patients [23], and 2–8% in FTC patients, relatively lower, are more incline to the occurrence of hematogenous metastasis and low-frequency occurrence of LNM [24, 25]. In contrast, MTC patients have a much higher incidence of cervical LNM, reaching 70% [26, 27]. LNM is recognized as an independent risk factor for the high mortality rate of ATC, a rare disease with a very poor prognosis [28]. This study demonstrated that among the 3 026 cases, the incidence of CLNM was 38.7%, and that of LLNM was 15.0%. Cervical LNM is the main risk factor for the high recurrence rate of thyroid carcinoma. If the potential LNM is ignored, the reoperation will be almost inevitable, which might produce the increase both in the difficulty of surgery and in the risk for complications such as recurrent laryngeal nerve injury and parathyroid function decline. Therefore, an accurate preoperative evaluation of LNM is conducive to the preoperative staging of thyroid carcinoma, and has extensive reference for the selection of surgical methods and the prognosis of patients. This study thus conducted a retrospective analysis of 3 026 patients with thyroid carcinoma to investigate the relationship between risk factors for LNM and the clinical characteristics of patients and then provide some reference for the selection of surgical operations for thyroid carcinoma. We found that male, age<55 years, tumor size >10 mm, bilateral lesions, and extrathyroidal extension had a higher risk of cervical LNM, while the multifocality, adenomatous nodules, and HT had no significant effect on LNM. Mao et al. reported that capsule invasion and extrathyroidal extension were the two major risk factors for LNM in PTC, and some other studies showed that HT was not related to LNM in PTC [29, 30], the results of which are both consistent with ours. The high coexistence between HT and PTC has been confirmed by many epidemiological studies, with the range from 20 to 85% [31]. Besides, research showed that the incidence of LNM in patients with PTC accompanied by HT was low [31], which might be due to a significantly larger number of removed lymph nodes from patients with HT and then a lower LNM rate in HT patients. Also, according to related literature, PTC or MTC patients with nodular goiter or follicular adenoma had a lower LNM rate [32]. However, based on our results, thyroid carcinoma patients with adenomatous nodules had a lower risk of CLNM than those without in the central cervical compartment (OR = 0.815, P = 0.045), and LLNM had no significant influence on them (OR = 1.015, P = 0.924). Based on the high incidence rate of CLNM and the and the limitations of routine preoperative detection methods, clinicians often opt for preventive central lymph node dissection. However, some studies have questioned the necessity of this procedure for low-risk PTC patients, as it does not show long-term improvement in patient prognosis and may increase the risk of complications such as hypocalcemia [33, 34]. Due to our findings that US, CECT and US combined with CECT have a diagnostic sensitivity of less than 45% for detecting CLNM, it is observed that male, age < 55 years old, tumor size >10 mm, bilateral lesions, and extrathyroidal extension had a higher risk of cervical LNM for thyroid cancer patients. As an important risk factor for LLNM, the number of CCLM is increasingly being included in risk stratification [35]. Therefore, we first suggested that patients with thyroid cancer who exhibit the aforementioned characteristics undergo preventive central lymph node dissection. Simultaneously, close attention should be paid to the involvement of lateral neck lymph nodes, which is beneficial for risk assessment and avoiding a second surgery that may affect the quality of life.

Second, to image the neck before thyroid carcinoma surgery is necessary to determine the appropriate scope of surgical resection. Based on the study that between two common preoperative imaging examinations of US and CECT, in the central, lateral and entire cervical compartments, US has a higher sensitivity, while CECT has a higher specificity. US is thus more effective in reducing the rate of missed diagnoses, while CECT helps avoid misdiagnosis. In the entire cervical region, US detected 610 metastases (20%), CECT identified 455 (15%), US combined with CECT revealed 692 cases (22%). The use of US combined with CECT only slightly improved detection compared to US alone, despite being statistically significative. A 2% absolute increase that does not justify radiation exposure in all patients. given the lack of economic analysis and the lack of safety data regarding radiation, contrast-induced acute kidney injury, contrast allergy, among other. Also, for certain pathologic types in PTC, the small size of the lymph node suggests overdiagnosis and upstaging of the disease, a disease that may stable for many years [36]. This study includes almost all types of thyroid cancer, although the sample size for types other than papillary cancer is relatively small. There may be variations in the response to lymph node metastasis among certain subtypes, potentially influencing overall survival. Further research is needed to determine which patient subgroups will benefit effectively from CT. The American Thyroid Association (ATA) guidelines in 2015 indicate that preoperative use of cross-sectional imaging studies (CT, MRI) with intravenous (IV) contrast is recommended as an adjunct to US for patients with clinical suspicion for advanced disease, including invasive primary tumor, or clinically apparent multiple or bulky lymph node involvement, to better characterize tumor invasion and bulky, inferiorly located, or posteriorly located lymph nodes. Preoperative knowledge of these features of the primary tumor or metastases could significantly influence the surgical plan [37]. According to what we discussed earlier that male, age < 55 years old, tumor size >10 mm, bilateral lesions, and extrathyroidal extension had a higher risk of cervical LNM for thyroid cancer patients. Therefore, this study supports the suggestion for preoperative contrast-enhanced computed tomography (CECT) examination for thyroid cancer patients possessing the aforementioned clinical characteristics. For thyroid cancer patients with these characteristics, a preoperative ultrasound combined with CECT examination is suggested. Iodine is generally cleared within 4–8 weeks in most patients, so concern about iodine burden from IV contrast causing a clinically significant delay in subsequent whole-body scans (WBSs) or RAI treatment after the imaging followed by surgery is generally unfounded [38]. By comprehensively evaluating the findings from both modalities, clinicians can make better clinical decisions and select individualized treatment approaches. In this study, ultrasonography and CECT were used to diagnose CLNM, with mean lymph node sizes of 5.4 and 6.7 mm, respectively. The sensitivity to CLNM by US was 32.3%, while that by CECT was lower, which might be owing to the current lack of uniform standard for LNM. Some literatures have reported a higher sensitivity of CECT, which could be attributed to the previous studies’ use of a 5 mm threshold for the central cervical compartment. [16]. However, relying solely on size criteria may not be appropriate for determining CLNM, and the lower sensitivity of CECT in detecting CLNM might be due to the complex anatomical structure at the chest entrance and the relatively small lymph nodes. Although CT is better able to visualize the entire neck region, its ability to interpret imaging results for small lymph nodes is inferior to ultrasound. CT imaging is less sensitive to CLNM than US imaging, which is consistent with the results of some previous studies [39, 40]. Both methods often exhibit lower diagnostic accuracy for CLNM compared to LLNM, consistent with previous studies. [41, 42]. Moreover, a considerable number of studies have shown that LLNM is likely to increase the risk of local recurrence and reduce the survival rate [43], and the recurrence rate of LLNM positive patients is significantly higher than that of CLNM patients [12]. In this study, the sensitivity and specificity of US in the LLNM detection are as high as 93.1% and 95.3%, correspondingly, which might result in a comparatively low rate of missed diagnosis and avoidance of misdiagnosis. Therefore, as the final conclusion, US imaging is finally suggested to be the preferred imaging method for assessing LLNM in patients with thyroid carcinoma.

The current study exposes several limitations. Firstly, due to the technical problems related to lymph node dissection, the lymph nodes evaluated cannot directly correspond with those pathologically examined, while the anatomical area of cervical lymph nodes is specially marked in surgery and imaging data. Second, except for PTC, the incidence rate of the types of thyroid carcinoma is relatively low, only 28 FTC patients, 3 ATC patients and 33 MTC patients enrolled in this study. Third, regardless of the imaging evaluation of LNM, it is necessary to perform lateral cervical dissection for all patients, then obtaining the real sensitivity value in the detection of the lateral neck. The final limitation is that the lateral cervical lymph node dissection was only performed in patients with pathologically proven LNM. For patients who did not undergo LLNM dissection, a negative LLNM result in the early postoperative imaging review is assumed to be a true negative. However, if LLNM is detected during long-term follow-up, it could be due to a false negative result in the preoperative assessment or it may indicate disease recurrence itself.