In our study, we investigated the detailed imaging features of emphysema in CPFE, with comparsion to COPD, and our results showed paraseptal emphysema was the most common form in CPFE, with an incidence statistically higher than that of COPD (p=0.001). Homogeneous emphysema was common in both the CPFE (73.8%) and COPD groups (52.5%), and it showed a higher incidence in CPEF group (p=0.004). The extent of emphysema in each lung lobe in the CPFE group was statistically less than that in the COPD group (p<0.01).
Due to the histopathological heterogeneity of CPFE, researchers often rely on HRCT for the diagnosis of CPFE, rather than using a pathological diagnosis [14–17]. HRCT can be used to visualize early changes in emphysema, as well as the in-depth details of interstitial pneumonia. HRCT thus plays a fundamental role in diagnosis of CPFE syndrome. Choi et al. [17] suggested the following diagnostic criteria based on HRCT: an area of emphysema with a reduced translucency clearly demarcated from adjacent normal lung tissue with a very thin wall (<1 mm) or no wall, and/or multiple pulmonary bullae (>1 cm) in the upper lobe. Centrilobular emphysema is a long-term, progressive lung disease and is considered to be a form of COPD, and studies [9, 12] have shown that centrilobular emphysema and/or bullous emphysema occurring predominantly in the upper lung is seen as a focal low-density area clearly demarcated from normal lung tissue, with visibly thin walls (<1 mm) or no wall.
Paraseptal emphysema (seen as low-attenuation areas in the subpleural zone) has been described in a majority of CPFE reports [1], and Araki [11] suggest that paraseptal emphysema is a typical feature of CPFE. However, determination of the emphysema type in CPFE is often very difficult because of alteration of its features due to coexisting fibrosis [18]. In spite of this difficulty, the presence of thick-walled large cysts—2 cm or more in diameter and delimitated by a wall 1 mm or more in thickness—in an area of the lung where reticulation is present, is considered to be one of the characteristic features of CPFE [19]. Based on the analysis of emphysema types in CPFE patients, this current study revealed that paraseptal type emphysema is the most common, a finding consistent with other studies [11, 13]. And we also used COPD as control to further pove the emphysema differences between the two enteties.
In our study, by using the thoracic VCAR post-processing software, we found that homogeneous emphysema was the main type in CPFE patients. This research has not been conducted before between CPFE and COPD. In addition, the emphysema volume was lower than that of COPD patients. This may be due to the different pathological mechanisms of emphysema formation by the two diseases. Although both can lead to poor alveolar elasticity, valve action caused by chronic bronchiolitis might also contribute to the pathogenesis of COPD. A larger sample study is required to confirm this hypothesis.
This study also explored the incidence of lung cancer in CPFE patients. Our results show that CPFE patients are more likely to develop lung cancer, compared with COPD patients, with squamous cell carcinoma being the most commonly seen. These results are consistent with previous studies published by Kwak et al. [20]. Upon analyzing the relationship between multiple factors of CPFE and lung cancer, we found that lung cancer incidence is higher in homogeneous emphysema patients and increases both with the severity of pulmonary interstitial fibrosis and the number of years of smoking. We speculated that homogeneous emphysema, severe fibrosis, and length of smoking history are the principal risk factors for lung cancer in CPFE patients. The diffuse pulmonary interstitial fibrosis seen in CPFE often presents as reticular blurry shadows, honeycomb patterns, distortion of alveolar structures in the subpleural and lower lobe, and/or traction bronchial or bronchiolar dilation [13, 19]. Focal ground glass opacity and/or alveolar consolidation may also occur but is not the primary manifestation. Occasionally, ground-glass opacity can be the only evidence of interstitial lung disease, and in this situation, lung biopsy becomes necessary [21]. In a few cases, pulmonary nodules and consolidation have also been found in CPFE, findings which are correlated with a higher incidence of lung cancer [20].
Previous studies have shown that smoking is closely related to the occurrence of CPFE and lung cancer. However, further research is needed to describe the correlation of homogeneous emphysema, degree of fibrosis, and lung cancer incidence. This information would contribute to both earlier detection of lung cancer and earlier treatment of patients, making increased survival of CPFE patients possible.
The limitations of this study include small sample size, and lack of in-depth characterization of interstitial fibrosis. In future study, we should conduct further investigation.