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VPI has been regarded as an adverse prognostic factor in LA because of the potential increased risk of cancer recurrence and reduced overall survival, even in small lung neoplasms no more than 2 cm in diameter or with ground-glass opacity [8, 13]. Kudo et al. established that patients with VPI may exhibit a broader spectrum of LN metastases due to tumors near the pleura spreading quickly through the extensive network of lymphatic vessels in the visceral pleura [14]. Assessing the likelihood of pleural infiltration is important for surgical decisions, treatment selection, and prognosis [15]. However, traditional intraoperative pathological frozen section diagnosis of VPI is time-consuming and inaccurate, with a reported accuracy rate of 56.5% [16]. The current gold standard for diagnosing VPI still involves postoperative staining of elastic fibers. The precise preoperative assessment in cases of adjacent pleural-associated lung cancer using imaging techniques could significantly influence surgical decision-making, a task that remains changeling. Subpleural LA typically manifests as pGGN that, because of their limited invasiveness, do not breach the visceral pleura [17, 18]. Thus, the study population was limited to patients with peripheral pleural-associated LA at clinical stage Ia and excluding pGGN.
Seok et al. identified several key CT features, including pleural contact, pleural thickening, solid proportion > 50%, and nodule size > 2 cm, as significant indicators of VPI in T1 peripheral LA [19]. Yanagawa et al. demonstrated a strong association between subsolid nodules with a consolidation-to-tumor ratio > 63% and VPI [20]. Manac'h et al. found that larger tumors were more likely to have VPI, with rates of 10.4% for tumors < 3 cm, 19.6% for tumors between 3 and 5 cm, and 33% for tumors > 5 cm [21]. In our investigation, no statistically significant disparities were observed between VPI with the proportions of solid components, maximum tumor diameters, or maximum consolidation diameters. These incongruous outcomes may be attributed to variations in inclusion criteria and potential sample selection bias. Our study exclusively enrolled peripheral LA nodules smaller than 3cm while excluding pGGN and those unrelated to the pleura. Furthermore, no association was identified in our study between CT semantic features of primary tumors and VPI, aligning with prior research findings indicating that spiculation, lobulation, and air bronchogram were not reliable indicators for evaluating VPI [22–24]. Air bronchogram is characterized by tumor cells spreading in a convoluted manner along bronchioles and alveoli without disrupting the lung architecture, and is correlated with the less invasive nature of LA [25]. Conversely, the presence of lobulation and spiculation signifies irregular tumor growth, with tumor cells infiltrating nearby blood and lymphatic vessels, suggesting a higher degree of invasiveness [26]. Nevertheless, the extent of tumor invasiveness alone does not comprehensively capture the true nature of VPI. Thus, this study placed greater emphasis on analyzing the CT semantic features surrounding the tumor.
Previous research [27, 28] has highlighted the significance of factors such as the DLP, as well as the angle and length of the contact interface, in predicting VPI, findings which align with our results. Hsu and Zhao et al. [29, 30] have underscored the potential utility of pleural attachment and indentation as valuable adjuncts for enhancing the early diagnostic accuracy of VPI in NSCLC. However, our study found no significant correlation between the pleural indentation and VPI. Pleural indentation is the result of the thickening of interlobular septa, which extends from the tumor surface to the pleural surface and introduces tension to the pleura [16].The association between pleural indentation and lesion malignancy remains a topic of debate. Gallagher et al. [31] suggested that elastosis, inflammatory invasion, and thick fibroblast proliferation contribute to pleural indentation, which consequently is only a reflection of pleural fiber tension, not VPI. Pleural attachment has been determined to be a significant risk factor for VPI in both univariate and multivariate regression analyses, surpassing DLP in predictive value due to the enhanced conditions for pleural invasion resulting from direct contact. Although many studies [29, 32, 33] have focused on the morphological characteristics of VPI as depicted on CT images, the accuracy remains limited, with the identified morphological features being subject to the expertise and interpretation of radiologists.
The close proximity of the tumor to the pleura posed difficulties in precisely delineating the ROI encompassing the tumor. As a result, this radiomics study specifically concentrated on the internal characteristics of the tumor. The utilization of Spearman pairwise correlation, mRMR method, and LASSO regression analysis served to enhance the efficacy of the feature selection process and mitigate feature redundancy, ultimately leading to the identification of five optimal quantitative radiomics features, namely total energy, skewness, large area low gray level emphasis (LALGLE), dependence non uniformity normalized (DNUN), and dependence entropy. These features encompass characteristics ranging from first-order to higher-order texture, aligning partially with findings from Wei et al.'s prior investigation [34]. Skewness and total energy are classified as first-order parameters, with lower values indicating greater lesion heterogeneity. LALGLE, a parameter of the GLSZM, also reflects lesion heterogeneity, with higher values indicating increased heterogeneity. The dependence entropy and DNUN, calculated from the GLDM, demonstrate the relationship between the gray-level intensity of CT voxels and the invasiveness of GGN. A higher value of these features suggests increased heterogeneity in texture patterns, which indicating malignant trait of tumors, encompasses localized variances in tumor proliferation, metabolic activity, cell apoptosis, and blood supply [35]. No shape category feature was identified as the optimal feature, potentially due to the morphological similarities and overlaps between VPI and Negative group, similar with the CT semantic findings. We constructed a nomogram model based on radiomics and peritumoral semantic features to identify VPI in peripheral LA patients with clinical stage Ia. The pairwise Delong test evaluation showed that the AUC value of the combined model was significantly higher than that of the radiomics model (p < 0.05).
However, our study has certain limitations. It is important to note that this study is retrospective in nature, which may introduce selection bias. Additionally, variations in CT scanning devices and acquisition protocols could impact the consistency of radiomics features. Furthermore, the feasibility and reproducibility of volume segmentation in clinical practice may be limited, with potential time constraints. Collaborative multi-center research is necessary to confirm the reliability and generalizability of the predictive model proposed in this study.