Semiquantative Visual Assessment of Sub-solid Pulmonary Nodules ≦3 cm in Differentiation of Lung Adenocarcinoma Spectrum

Abstract

We aimed to analyze CT features of persistent subsolid nodules (SSN) ≦3 cm diagnosed pathologically as adenocarcinoma spectrum to investigate whether parameters enable distinction between invasive pulmonary adenocarcinomas (IPAs) and pre-invasive lesions. A total of 129 patients with 141 SSNs confirmed with surgically pathologic proof were retrospectively reviewed. Of 141 SSNs, there were 57 pure ground-glass nodules (GGNs), 22 heterogeneous GGNs, and 62 part-solid nodules. SSN subclassification showed a significant linear trend with invasive degree of the adenocarcinoma spectrum (pure GGNs 7%; heterogeneous GGNs 36.4%; part-solid nodules 85.5%, P for trend <0.0001). For IPA detection in 141 SSNs, a solid part of ≧3 mm was the most specificity (sensitivity, 76.9%; specificity, 94.7%), followed by air-bronchogram sign (sensitivity, 53.8%; specificity, 89.5%), SSN subclassification (sensitivity, 81.5%; specificity, 88.2%), and a lesion size ≧12 mm (sensitivity, 84.6%; specificity, 76.3%). For IPA detection in 79 pure or heterogeneous GGNs, the heterogeneous GGN sign was the most useful finding, with most specificity (sensitivity, 66.7%; specificity, 79.1%), followed by CT attenuation (HU) of ≧-493 (sensitivity, 75%; specificity, 74.6%) and a lesion size ≧10 mm (sensitivity, 83.3%; specificity, 70.1%). In conclusion, this simple combined visual and semiquantitative analysis of CT features helps distinguish IPAs from pre-invasive lesions.

Figure 1

First, to determine the radiologic features of SSNs according to the subclassification system into three different categories. Second, the lesion size with cut-off value of ≧10 mm, the type of heterogeneous GGN, and the higher HU value with cut-off value of ≧−493 in the pure and heterogeneous GGNs were the optimal diagnostic threshold for IPA lesions prediction with high NPV, which could help to rule out IPAs. Third, the lesion size with cut-off value of ≧12 mm, the type of part-solid nodule, and the solid part with cut-off value of ≧3 mm, presence of air-bronchogram in all SSNs were the optimal diagnostic threshold for IPA lesions prediction with moderate to high PPV, which could help to rule in IPAs. Fourth, the diagnostic scheme of part-solid nodules followed the rules of the SSNs.

Figure 2

An example of subsolid nodule with an air bronchogram sign according to the SSN subclassification. A 61-year-old woman had a 1.4 cm part-solid nodule in RUL. The (A) coronal and (B) oblique images showed an internal air bronchogram inside the lesion. The patient underwent video-thoracoscopic wedge resection of RUL. Further pathologic report demonstrated invasive pulmonary adenocarcinoma in RUL, Stage 1. Abbreviations: SSN = subsolid nodule; RUL = right upper lobe.

Figure 3

An example of subsolid nodule with abnormal cystic-like airspace according to the SSN subclassification. A 55-year-old man had a 1.1 cm part-solid nodule in RLL. The axial CT image showed an abnormally dilated cystic-like airspace inside the lesion. The patient underwent video-thoracoscopic wedge resection of RLL. Further pathologic report demonstrated invasive pulmonary adenocarcinoma in RLL, Stage 1. Abbreviations: SSN = subsolid nodule; RLL = right lower lobe.

Figure 4

An example of pure GGN according to the SSN subclassification. A 60-year-old woman had a 1.3 cm pure GGN nodule in RML. The LDCT images showed homogenous groundglass opacities only when viewed on the lung window (Fig. 3A), but not seen on the mediastinal window (Fig. 3B). The average CT attenuation values (min, max and mean) expressed in HU were measured by placing a ROI of 15 mm² on the lesion. In addition, to avoid placing the ROI box in or near the blood vessels could reduce the measurement errors (Fig. 3C). The patient underwent video-thoracoscopic wedge resection of RML. Further pathologic report demonstrated minimally invasive adenocarcinoma in RML. Abbreviations: GGN: groundglass nodule; SSN = subsolid nodule; RML = right middle lobe; ROI = region of interest; HU = Hounsfield unit.

Figure 5

An example of heterogeneous GGN according to the SSN subclassification. A 66-year-old man had a 1.2 cm heterogeneous GGN nodule in RUL. The LDCT images showed heterogeneous groundglass opacities with focal solid component only when viewed on the lung window (Fig. 4A), but not seen on the mediastinal window (Fig. 4B). The average CT attenuation values (min, max and mean) expressed in HU were measured by placing an ROI of 15 mm² on the lesion (Fig. 4C). In addition, to avoid placing the ROI box in or near the blood vessels could reduce the measurement errors. The patient underwent video-thoracoscopic wedge resection of RUL. Further pathologic report demonstrated invasive pulmonary adenocarcinoma in RUL. Abbreviations: GGN: groundglass nodule; SSN = subsolid nodule; RUL = right upper lobe; ROI = region of interest; HU = Hounsfield unit.