Computed tomography attenuation predicts the growth of pure ground-glass nodules

Abstract

Objectives

Cases of lung cancer with pure ground-glass nodules (GGNs) have been detected with increasing frequency since the advent of computed tomography (CT), and growth is sometimes noted during follow-up. The objective of this study was to evaluate the potential predictive factors for pure GGN growth.

Materials and methods

We retrospectively examined 124 cases involving pure GGNs. Patients were monitored for >2 years using high-resolution CT. After a median follow-up period of 57.0 months, GGNs showed growth in 64 of the 124 cases. We compared the patient characteristics and tumor properties of cases with and without growth. The predictive value of the mean CT attenuation for GGN growth was evaluated using receiver operating characteristic curve analysis.

Results

Univariate analysis revealed significant differences between mean CT attenuation values in patients with and without growth (−602.9 ± 90.7 Hounsfield units [HU] vs −705.7 ± 77.7 HU, P < 0.0001). The final incidence of growth was estimated to be significantly higher for lesions with a mean CT attenuation value of ≥−670 HU (n = 62; 93.2%) than for lesions with values of <−670 HU (n = 62; 31.6%; P < 0.0001). The sensitivity and specificity for predicting tumor growth using this cutoff value were 78.1% and 80.0%, respectively (area under the curve, 0.81).

Conclusion

The mean CT attenuation value could be useful in predicting the growth of GGNs.

Introduction

We previously evaluated the usefulness of computed tomography (CT) as a screening tool for lung cancer [1], [2]. Cases of lung cancer involving ground-glass nodules (GGNs) have been detected with increasing frequency since the advent of CT. However, the natural history of GGNs has not yet been fully elucidated. Pulmonary adenocarcinomas, which often present with GGNs during radiologic investigation, regularly show involvement of neoplastic cells on histologic examination. These neoplastic cells are usually distributed along pre-existing alveolar structures in a pattern referred to as a “lepidic growth pattern” [3]. It is thought that pulmonary lepidic growth tumors progress in a stepwise fashion from adenocarcinoma in situ to invasive adenocarcinoma [3], [4]. Previous studies have reported cases in which pure GGNs progressed [5], [6], [7], and long-term follow-up investigations gradually elucidated the natural history of pure GGNs [8], [9], [10], [11]. Recently, the Fleischner Society published recommendations for the management of subsolid pulmonary nodules detected on CT [12]. However, it is not yet possible to ascertain which GGNs will progress to solid tumors, and there are no known prognostic factors that can predict the growth of adenocarcinoma from a non-invasive to an invasive type.

To address the current lack of knowledge regarding the natural history of GGNs, we retrospectively reviewed the characteristics and CT findings of patients with pure GGNs who were followed up for a long period of time (>24 months).