Multidetector CT features of pulmonary focal ground-glass opacity: differences between benign and malignant

Objective

To evaluate different features between benign and malignant pulmonary focal ground-glass opacity (fGGO) on multidetector CT (MDCT).

Methods

82 pathologically or clinically confirmed fGGOs were retrospectively analysed with regard to demographic data, lesion size and location, attenuation value and MDCT features including shape, margin, interface, internal characteristics and adjacent structure. Differences between benign and malignant fGGOs were analysed using a χ² test, Fisher''s exact test or Mann–Whitney U-test. Morphological characteristics were analysed by binary logistic regression analysis to estimate the likelihood of malignancy.

Results

There were 21 benign and 61 malignant lesions. No statistical differences were found between benign and malignant fGGOs in terms of demographic data, size, location and attenuation value. The frequency of lobulation (p=0.000), spiculation (p=0.008), spine-like process (p=0.004), well-defined but coarse interface (p=0.000), bronchus cut-off (p=0.003), other air-containing space (p=0.000), pleural indentation (p=0.000) and vascular convergence (p=0.006) was significantly higher in malignant fGGOs than that in benign fGGOs. Binary logistic regression analysis showed that lobulation, interface and pleural indentation were important indicators for malignant diagnosis of fGGO, with the corresponding odds ratios of 8.122, 3.139 and 9.076, respectively. In addition, a well-defined but coarse interface was the most important indicator of malignancy among all interface types. With all three important indicators considered, the diagnostic sensitivity, specificity and accuracy were 93.4%, 66.7% and 86.6%, respectively.

Conclusion

An fGGO with lobulation, a well-defined but coarse interface and pleural indentation gives a greater than average likelihood of being malignant.With the availability of low-dose spiral CT scan of the lung, focal ground-glass opacity (fGGO) that was difficult to detect on conventional chest radiographs has increasingly been detected [1-3]. Ground-glass opacity (GGO) is defined as an area of a slight homogeneous increase in density, which does not obscure underlying bronchial structures or vascular margins on high-resolution CT (HRCT) [4]. Pathologically, GGO may be caused by partial airspace filling, interstitial thickening with inflammation, oedema, fibrosis, neoplastic proliferation, the normal respiratory condition or increased pulmonary capillary blood volume [5]. GGO can be classified as pure GGO (pGGO) or mixed GGO (mGGO) based on the presence of solid components. Although GGO is a common and non-specific finding of lung HRCT, and may occur in benign lung conditions such as organising pneumonia, focal fibrosis and haemorrhage [6-8], it has recently received considerable attention because it may indicate an early underlying lung cancer, which in most cases presents as bronchioloalveolar carcinoma (BAC) and adenocarcinoma with a predominant BAC component. It was reported in a study [9] that 17 of 28 pGGOs were BAC, 3 were adenocarcinoma and 8 were atypical adenomatous hyperplasia (AAH). Several other studies [10,11] have also indicated that mGGOs are more likely to be malignant, with the malignant rate of pGGO and mGGO being 18% and 63%, respectively [12]. The aim of the present study was to retrospectively compare the features of benign and malignant fGGOs on thin section multidetector CT (MDCT) images in an attempt to identify characteristics that would help the differential diagnosis of fGGOs.