Dual-energy computed tomography could reliably differentiate metastatic from non-metastatic lymph nodes of less than 0.5 cm in patients with papillary thyroid carcinoma

Abstract

Background: Dual-energy computed tomography (DECT) has been widely applied to detect lymph node (LN) and lymph node metastasis (LNM) in various cancers, including papillary thyroid carcinoma (PTC). This study aimed to quantitatively evaluate metastatic cervical lymph nodes (LNs) <0.5 cm in patients with PTC using DECT, which has not been done in previous studies.

Methods: Preoperative DECT data of patients with pathologically confirmed PTC were retrospectively collected and analyzed between May 2016 and June 2018. A total of 359 LNs from 52 patients were included. Diameter, iodine concentration (IC), normalized iodine concentration (NIC), and the slope of the energy spectrum curve (λ_HU) of LNs in the arterial and the venous phases were compared between metastatic and non-metastatic LNs. The optimal parameters were obtained from the receiver operating characteristic (ROC) curves. The generalized estimation equation (GEE) model was used to evaluate independent diagnostic factors for LNM.

Results: A total of 139 metastatic and 220 non-metastatic LNs were analyzed. There were statistical differences of quantitative parameters between the two groups (P value 0.000-0.007). The optimal parameter for diagnosing LNM was IC in the arterial phase, and its area under the curve (AUC), sensitivity, and specificity were 0.775, 71.9%, and 73.6%, respectively. When the three parameters of diameter, IC in the arterial phase, and NIC in the venous phase were combined, the prediction efficiency was better, and the AUC was 0.819. The GEE results showed that LNs located in level VIa [odds ratio (OR) 2.030, 95% confidence interval (CI): 1.134-3.634, P=0.017], VIb (OR 2.836, 95% CI: 1.597-5.038, P=0.000), diameter (OR 2.023, 95% CI: 1.158-3.532, P=0.013), IC in the arterial phase (OR 4.444, 95% CI: 2.808-7.035, P=0.000), and IC in the venous phase (OR 5.387, 95% CI: 3.449-8.413, P=0.000) were independent risk factors for LNM in patients with PTC.

Conclusions: DECT had good diagnostic performance in the differentiation of cervical metastatic LNs <0.5 cm in patients with PTC.

Keywords: Papillary thyroid carcinoma (PTC); dual-energy computed tomography (DECT); iodine concentration (IC); lymph nodes (LNs); metastasis.

Figure 1

Flowchart showing the inclusion and exclusion criteria of lymph nodes in patients with PTC in the current study. DECT, dual-energy computed tomography; PTC, papillary thyroid carcinoma.

Figure 2

A patient with PTC of the right lobe was confirmed by postoperative pathology, with metastatic lymph nodes in the right level VIb (3/3). (A,B,C) Iodine maps in the arterial phase. An ovoid region of interest (yellow; area, 9 mm²) was placed on the solid part in combined axial (A), sagittal (B), and coronal (C) images, including the entire lymph node as large as possible, and avoiding peripheral fat, cystic, necrosis, and calcification. (D,E,F) Iodine maps in the venous phase. The short diameter was 0.4 cm. In this case, the iodine concentration was 6.5 mg/mL in the arterial phase and 4.7 mg/mL in the venous phase. PTC, papillary thyroid carcinoma

Figure 3

Box plots showing that IC in the arterial and the venous phases (A), NIC in the arterial and the venous phases (B), λ_HU in the arterial and the venous phases (C), and diameter (D) had statistical significance in the prediction of metastatic and non-metastatic lymph nodes. *, P<0.05; **, P<0.002; ***, P<0.001. IC, iodine concentration; IAP, in the arterial phase; M, metastasis; IVP, in the venous phase; NIC, normalized iodine concentration; λ_HU, the slope of energy spectrum curve.

Figure 4

The ROC curve of IC in the arterial phase was used to identify metastatic and non-metastatic lymph nodes. When the cut-off value was 2.1 mg/mL, the sensitivity, specificity, and accuracy were 73.63%, 71.94%, and 72.59%, respectively. ROC, receiver operating characteristic; IC, iodine concentration; AUC, area under the curve.

Figure 5

Typical dual-energy CT images and iodine maps of metastatic lymph node with a diameter of 0.47 cm in a 51-year-old woman with PTC. (A) Contrast-enhanced monochromatic image in the arterial phase of a metastatic lymph node (area, 12 mm², CT value, 88.9±12.1 HU). (B) Iodine map in the arterial phase of a metastatic lymph node (area, 12 mm²; iodine concentration, 5.7 mg/mL). (C) Contrast-enhanced monochromatic image in the venous phase of a metastatic lymph node (area, 12 mm², CT value, 78.6±15.1 HU). (D) Iodine map in the venous phase of a metastatic lymph node (area, 12 mm²; iodine concentration, 3.5 mg/mL). CT, computed tomography; PTC, papillary thyroid carcinoma.

Figure 6

Typical dual-energy CT images and iodine maps of non-metastatic lymph node with a diameter of 0.31 cm in a 37-year-old woman with PTC. (A) Contrast-enhanced monochromatic image in the arterial phase of a metastatic lymph node (area, 15 mm², CT value, 40.2±7.2 HU). (B) Iodine map in the arterial phase of a metastatic lymph node (area, 15 mm²; iodine concentration, 0.8 mg/mL). (C) Contrast-enhanced monochromatic image in the venous phase of a metastatic lymph node (area, 15 mm², CT value, 61.4±6.5 HU). (D) Iodine map in the venous phase of a metastatic lymph node (area, 15 mm²; iodine concentration, 1.3 mg/mL). CT, computed tomography; PTC, papillary thyroid carcinoma.