Detection of Residual Lymph Node Metastases in High-Risk Papillary Thyroid Cancer Patients Receiving Adjuvant I-131 Therapy: The Usefulness of F-18 FDG PET/CT

Determining the Minimum Number of Examined Lymph Nodes for N1b Papillary Thyroid Cancer Patients

BACKGROUND

This study aimed to evaluate the correlation between the number of examined lymph nodes (eLNs) and postoperative residual lateral LN disease in patients with papillary thyroid cancer (PTC) and lateral nodal metastasis (N1b) and determine the minimal threshold for the eLNs.

METHODS

Patients diagnosed with unilateral N1b PTC who underwent total thyroidectomy with therapeutic LN dissection of the central and lateral compartments between January 2012 and December 2022 were included. Multivariate logistic regression analyses were performed to identify the threshold number of eLNs that independently influenced the risk of residual lateral LN disease.

RESULTS

Residual lateral LN disease was identified in 56 (5.4%) of 1042 T1-2 patients and 74 (12.3%) of 602 T3-4 patients. When analyzed as a continuous variable, the number of eLNs in the lateral neck was independently associated with a reduced risk of residual lateral LN disease in both T1-2 (OR: 0.93; 95% CI: 0.90-0.97; p < 0.001) and T3-4 patients (OR: 0.94; 95% CI: 0.91-0.97; p < 0.001). As a categorical variable, the risk of residual lateral LN disease continued to decrease significantly until the number of eLNs reached 34 in T1-2 patients and 46 in T3-4 patients.

CONCLUSION

Comprehensive preoperative imaging for LN status and systematic compartmental dissection of the affected levels are critical in managing N1b PTC. To minimize the risk of residual lateral LN disease, the minimum recommended number of eLNs in the lateral neck is 34 for T1-2 patients and 46 for T3-4 patients.

LEVEL OF EVIDENCE

4-retrospective cohort study.

Surveillance for Differentiated Thyroid Cancer Recurrence

Serum thyroglobulin monitoring along with anatomic and functional imaging play key roles in the surveillance of patients with differentiated thyroid cancer after initial treatment. Among patients with a disease stage justifying thyroid remnant ablation or with suspected metastatic disease, radioiodine whole-body scans are essential in the months after surgery. For patients with low to moderate-risk cancers, ultrasonography of the neck (with measurement of serum thyroglobulin on thyroid hormone replacement) are the best initial diagnostic modalities, and are often the only tests required. In individuals suspected of having distant metastases, CT, MRI, and 18F-FDG PET can make important contributions in localizing residual disease and monitoring its progression and responses to therapy, provided they are used in the appropriate setting.

Both F-18 FDG-avidity and Malignant Shape of Cervical Lymph Nodes on PET/CT after Total Thyroidectomy Predict Resistance to High-dose I-131 Therapy in Patients with Papillary Thyroid Cancer

Objective:

Resistance of metastatic lymph nodes (LNs) to high dose I-131 therapy is associated with high morbidity in patients with differentiated thyroid cancer. We evaluated the role of F-18 FDG PET/CT in the prediction of resistance to high dose I-131 therapy in patients with papillary thyroid cancer.

Methods:

The subjects were 307 patients who underwent total or near total thyroidectomy followed by high dose (5.55-6.66 GBq) I-131 therapy. We divided the patients into three subgroups by visual assessment of regional LNs: FDG-avid LNs with a malignant shape on CT (PET/CT-positive group), FDG-avid LNs with a benign shape on CT (PET/CT-intermediate group) and no FDG-avid lesion (PET/CT-negative group). We measured the maximum SUV (SUVmax) of FDG-avid LNs in each patient. The presence or absence of focal increased uptake of I-131 was evaluated by whole body scan (WBS), and was denoted as WBS-positive group or WBS-negative group, respectively. Resistance to therapy was defined as presence of thyroglobulin (Tg) in serum (Tg ≥1.0 ng/ml) 3-6 months after I-131 therapy. Univariate and multivariate analyses were performed to determine the relationship between resistance to I-131 therapy and various clinico-pathologic variables.

Results:

PET/CT-positive, intermediate, and negative groups included 20 (6.5%), 44 (14.3%) and 243 (79.2%) patients, respectively. The mean SUVmax was significantly higher in the PET/CT-positive group than that of the PET/CT-intermediate group (4.6 vs. 2.7, P <0.001). Univariate analysis revealed that the PET/CT-positive group (P <0.001), T2-4 stage (P <0.001), N1b stage (P = 0.001), lower dose (5.55 GBq) of I-131 (P <0.001), and the WBS-positive group (P = 0.029) were associated with resistance to therapy. In multivariate analysis, the PET/CT-positive group, lower dose of I-131, N1b stage, and T2-4 stage remained significant with odds ratios of 10.07 (P <0.001), 3.82 (P <0.001), 3.58 (P = 0.001), and 2.53 (P = 0.009), respectively.

Conclusion:

FDG-avidity and malignant shape of cervical LNs on pre-therapy FDG PET/CT were a strong risk factors predicting resistance to high dose I-131 therapy. A lower dose of administered I-131 (5.55 GBq) and more extensive tumors (T2-4 and N1b) were also associated with resistance to high dose I-131 therapy.

Impact of patient age on the iodine/FDG "flip-flop" phenomenon in lung metastasis from thyroid cancer

OBJECTIVES

Radioiodine therapy is an effective treatment for lung metastasis from thyroid cancer. However, cases of lung metastasis without iodine uptake are often encountered. In such cases, FDG accumulation in lung lesions is often observed. There is a reverse relationship between iodine and FDG accumulation in thyroid cancer lesions, the so-called "flip-flop" phenomenon. The aim of this study was to assess the relationship between patient age and the occurrence of the flip-flop phenomenon.

METHODS

Eighty-six patients who underwent radioiodine therapy for lung metastasis were studied retrospectively (age 17-73 years; median 60 years; males:females 22:64). We compared the clinical data and imaging findings (size and FDG uptake of lung nodules) between patients with (n = 44) and without (n = 42) iodine uptake in lung metastasis.

RESULTS

Significantly more young patients showed iodine accumulation in lung metastasis than old patients (p = 0.0025). Lung metastases with larger size or greater FDG uptake showed no iodine uptake more frequently with significant difference (p = 0.015 and <0.001, respectively). Among patients with FDG uptake in the lung metastasis, 57.1 % of young patients (<60 years) and 24.3 % of the old patients (≥60 years) showed iodine uptake (p = 0.0029).

CONCLUSIONS

Higher patient age and lung nodules with large size or FDG accumulation are negative factors for iodine accumulation in lung metastases from thyroid cancer. In addition, our results show that young patients have a greater likelihood of iodine uptake even when FDG accumulates in lung metastasis, in contrast to old patients.

Usefulness of PET/CT in the diagnosis of recurrent or metastasized differentiated thyroid carcinoma

The aim of the present study was to determine the usefulness of the positron emission tomography/computed tomography (PET/CT) with ¹⁸F-fluorodeoxyglucose (FDG) in the detection of recurrence or metastasization of differentiated thyroid carcinoma (DTC) in patients with abnormal thyroglobulin levels and negative findings on the ¹³¹I-diagnostic whole-body scanning (dWBS). Fifteen patients with DTC, abnormal thyroglobulin levels, and negative ¹³¹I-dWBS findings were scanned using the ¹⁸F-FDG PET/CT. Positive diagnosis was based on postoperative histologic findings, and clinical and imaging follow-up results obtained in the subsequent 6 months. In addition, preoperative and postoperative thyroglobulin levels were compared. Using the findings of ¹⁸F-FDG PET/CT and data on confirmed positive diagnosis, sensitivity and positive predictive value (PPV) were calculated. Sensitivity and PPV of PET/CT in detecting recurrence or metastasisization of DTC were 93.30 and 91.40%, respectively. Furthermore, postoperative thyroglobulin levels were markedly lower compared to the preoperative levels (respectively, 4.67±1.71 vs. 58.53±18.34 ng/ml; p<0.05). PET/CT scan with ¹⁸F-FDG is an informative technique for the detection of recurrent or metastasized DTC in patients with abnormal thyroglobulin levels and negative ¹³¹I-dWBS findings.

Tumor location-dependent skip lateral cervical lymph node metastasis in papillary thyroid cancer

BACKGROUND

Lateral cervical lymph node metastasis without central lymph node (CLN) metastasis is not infrequent in papillary thyroid cancer (PTC). This study was designed to investigate the frequency and pattern of skip metastasis in PTC.

METHODS

We reviewed 131 patients who underwent total thyroidectomy with CLN dissection and selective lymph node dissection. Tumor location was classified in 3 areas (upper, middle, and lower third) based on preoperative ultrasonographic findings.

RESULTS

All skip metastases occurred in patients whose tumors had been on the upper part of the thyroid (p < .001). Among 9 patients with skip metastasis, level III lymph nodes (66.7%) were the lymph nodes that were most frequently involved in skip metastasis.

CONCLUSION

Primary tumors in the upper portion of the thyroid are closely linked to skip metastasis. Careful preoperative evaluation of lateral cervical lymph nodes is suggested when a tumor is in the upper portion.

Therapeutic impact of (18)F-FDG PET/CT in recurrent differentiated thyroid carcinoma

PURPOSE

(18)F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) has proved effective in detecting recurrent or metastatic differentiated thyroid carcinoma (DTC) in the follow-up of operated DTC patients with high thyroglobulin (Tg) levels and negative findings on radioiodine whole-body scan. The aim of this retrospective study was to assess the impact of PET/CT on the planning of appropriate treatment for known recurrent disease in operated DTC patients.

MATERIALS AND METHODS

The study concerned 44 consecutive DTC patients (36 papillary, 8 follicular), who underwent total thyroidectomy and thyroid remnant ablation with (131)I and PET/CT. All patients had proven or strongly suspected recurrent disease judging from neck ultrasound (US) and fine-needle aspiration cytology, and detectable basal Tg levels.

RESULTS

PET/CT findings were positive in 25/44 patients (56.81 %) and negative in 19. A positive PET/CT result predicted resectable tumour recurrences in 19/25 patients, but also detected additional tumour sites that prompted changes to the treatment plan in 6/25 patients (24 %). A negative PET/CT result led to clinical monitoring for 11/19 patients (57.89 %).

CONCLUSIONS

PET/CT can help select patients, who might benefit from a tailored therapy by improving the detection of local recurrences not apparent on neck US or metastases.

Role of [(18)F]-fluorodeoxy-D-glucose positron emission tomography and computed tomography in the early detection of persistent/recurrent thyroid carcinoma in intermediate-to-high risk patients following initial radioactive iodine ablation therapy

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) scan has a role in the surveillance of patients with a history of thyroid carcinoma. Its efficacy after remnant ablation as far as detecting persistent or recurrent thyroid carcinoma before other surveillance methods is not known, however. In intermediate-to-high risk thyroid carcinoma patients we studied whether PET/CT scan, performed 6-12 months after the first remnant ablation, could provide more information than ultrasonography (US) and thyrotropin-stimulated serum thyroglobulin (Tg) determination with diagnostic whole-body scan (DxWBS).

METHODS

We studied 71 subjects with differentiated thyroid cancer (DTC) who were intermediate-to-high risk for persistent/recurrent disease and who had received PET/CT scan, US, and DxWBS simultaneously with stimulated Tg levels 6-12 months after remnant ablation. To evaluate the diagnostic efficacy of PET/CT scan, the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy were calculated.

RESULTS

Ten subjects (14%) had persistent/recurrent disease detected 6-12 months after remnant ablation. Persistence/recurrence was detected in nine (12.7%) of these patients by conventional methods, including US and DxWBS, along with stimulated Tg levels. The remaining case was detected solely by a PET/CT scan, which showed a mediastinal prevascular lesion; this was confirmed by a therapeutic WBS after additional radioiodine therapy. Among the six patients whose PET/CT scan showed positive results, five had persistent/recurrent disease. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of PET/CT scan for detecting persistent/recurrent thyroid carcinoma were 50%, 98.4%, 83.3%, 92.3%, and 91.5%, respectively.

CONCLUSION

In intermediate-to-high risk patients with DTC seen 6-12 months after their first remnant ablation, there is almost no complementary role for adding a PET/CT scan to conventional follow-up methods, an US and a DxWBS simultaneously with stimulated Tg levels.