Diagnostic value of CT enhancement degree in lymph node metastasis of papillary thyroid cancer: A comparison of enhancement, ratio, and difference

OBJECTIVES: To evaluate the value of computed tomography (CT) enhancement degree in diagnosing lymph node (LN) metastasis in papillary thyroid carcinoma (PTC) by determining the ratio and difference between the Hounsfield units (HU) of CT enhancement and plain scan of the LNs, as well as between the HU of CT-enhanced LNs and the sternocleidomastoid muscle. METHODS: The plain and enhanced CT findings of 114 metastasis-positive LNs in 89 cases and 143 metastasis-negative LNs in 114 cases of PTC were analyzed retrospectively. Plain HU of LNs (PN(HU)), enhanced HU of LNs (EN(HU)), and enhanced HU of the sternocleidomastoid muscle (EM(HU)) were measured. The EN(HU), difference between EN(HU) and PN(HU) (EN-PN(HU)), ratio of EN(HU) to PN(HU) (EN/PN(HU)), difference between EN(HU) and EM(HU) (EN-EM(HU)), and ratio of EN(HU) to EM(HU) (EN/EM(HU)) in metastasis-positive and metastasis-negative LN groups were calculated, the corresponding diagnostic efficacy for differentiating metastasis-positive from metastasis-negative LNs in PTC were sought using the receiver-operating curve. The interobserver agreement between readers was assessed using the interobserver correlation coefficient (ICC). RESULTS: The EN(HU) of 114 metastasis-positive LNs and 143 metastasis-negative LNs was 113.39 ± 24.13 and 77.65 ± 15.93, EN-PN(HU) was 65.84 ± 21.72 HU and 34.07 ± 13.63 HU, EN/PN(HU) was 2.36 (1.98, 2.75) and 1.76 (1.54, 2.02), EN-EM(HU) was 49.42 ± 24.59 HU and 13.27 ± 15.41 HU, and EN/EM(HU) was 1.79 ± 0.40 and 1.21 ± 0.24, respectively (all P < 0.001). The area under the curve, cutoff value, sensitivity, specificity, and accuracy of EN(HU) for identifying metastasis-positive and metastasis-negative LNs were 0.895, 97.3 HU, 0.746, 0.895, and 0.829, EN-PN(HU) was 0.894, 47.8 HU, 0.807, 0.874, and 0.844, EN/PN(HU) was 0.831, 1.9, 0.877, 0.650, and 0.751, EN-EM(HU) was 0.890, 26.4 HU, 0.807, 0.839, and 0.825, and EN/EM(HU) was 0.888, 1.5, 0.728, 0.902, and 0.825, respectively. The readers had an excellent interobserver agreement on these five parameters (ICC = 0.874–0.994). CONCLUSION: In the preoperative evaluation of LN metastasis in PTC, EN(HU), EN-PN(HU), EN-EM(HU), and EN/EM(HU) had similarly high diagnostic efficacy, with EN(HU), EN-PN(HU), and EN/EM(HU) having higher specificity and EN-PN(HU) and EN-EM(HU) having higher sensitivity.