Diameter of the Solid Component in Subsolid Nodules on Low-Dose Unenhanced Chest Computed Tomography: Measurement Accuracy for the Prediction of Invasive Component in Lung Adenocarcinoma

Abstract

Objective: To determine if measurement of the diameter of the solid component in subsolid nodules (SSNs) on low-dose unenhanced chest computed tomography (CT) is as accurate as on standard-dose enhanced CT in prediction of pathological size of invasive component of lung adenocarcinoma.

Materials and methods: From February 2012 to October 2015, 114 SSNs were identified in 105 patients that underwent low-dose unenhanced and standard-dose enhanced CT pre-operatively. Three radiologists independently measured the largest diameter of the solid component. Intraclass correlation coefficients (ICCs) were used to assess inter-reader agreement. We estimated measurement differences between the size of solid component and that of invasive component. We measured diagnostic accuracy of the prediction of invasive adenocarcinoma using a size criterion of a solid component ≥ 6 mm, and compared them using a generalized linear mixed model.

Results: Inter-reader agreement was excellent (ICC, 0.84.0.89). The mean ± standard deviation of absolute measurement differences between the solid component and invasive component was 4 ± 4 mm in low-dose unenhanced CT and 5 ± 4 mm in standard-dose enhanced CT. Diagnostic accuracy was 81.3% (95% confidence interval, 76.7.85.3%) in low-dose unenhanced CT and 76.6% (71.8.81.0%) in standard-dose enhanced CT, with no statistically significant difference (p = 0.130).

Conclusion: Measurement of the diameter of the solid component of SSNs on low-dose unenhanced chest CT was as accurate as on standard-dose enhanced CT for predicting the invasive component. Thus, low-dose unenhanced CT may be used safely in the evaluation of patients with SSNs.

Keywords: Invasive component; Low-dose CT; Lung adenocarcinoma; Measurement; Subsolid nodule.

Fig. 1. Bland-Altman plots revealing variability in difference between size of pathologically invasive component and that of solid component in low-dose unenhanced (A) and standard-dose enhanced (B) CT.

Horizontal axes indicate size of pathologically invasive component as reference standard, while vertical axes indicate difference between size of pathologically invasive component and that of solid component. Solid lines = mean differences. Dashed lines = 95% limits of variability. CT = computed tomography, LDCT = low-dose unenhanced CT, SD = standard deviation, SDCT = standard-dose enhanced CT

Fig. 2. 68-year-old male patient diagnosed with minimally invasive adenocarcinoma.

Low-dose unenhanced (A) and standard-dose enhanced (B) CT images demonstrate subsolid nodule (arrowheads) in right upper lobe. All readers measured longest diameter of solid component as 5 mm, regardless of CT protocols. In photomicrograph (C), red dotted line represents border of invasive component. Areas between red and green dotted lines indicate lepidic component. Invasive component of tumor was measured as 5 mm (hematoxylin-eosin stain; original magnification, × 40).