## 4 Discussion  
Methods for the quantitative analysis of medical CT images are constantly expanding, and the applications of such methods in the thoracic field are increasing [4; 5; 9; 14; 17; 18; 19; 20; 21; 28; 30; 31; 32; 33; 34]. In clinical practice, quantitative CT analysis applications are most popular and most used for lung nodules [35; 36]. Among the quantitative CT applications for lung nodules, those related to persistent SSNs have garnered the most interest from radiologists and clinicians in the last five years [9; 14; 17; 18; 19; 20; 21; 22; 37; 38; 39; 40; 41]. This particular interest in persistent SSNs is because in most cases, these lesions correspond to the preinvasive or invasive peptide growth of pulmonary adenocarcinomas [9; 20]. This statement was also confirmed by our study, in which all surgically removed PSNs corresponded to minimally invasive or invasive adenocarcinoma (nine minimally invasive adenocarcinoma and three invasive adenocarcinoma graded as pT1a). Rarely, persistent SSNs may be the manifestation of benign lesions (organizing pneumonia/focal interstitial fibrosis) [42] or malignancies such as primitive pulmonary lymphomas [43] and pulmonary metastases from extrapulmonary malignancies [44]. Pulmonary adenocarcinomas presenting as SSNs exhibit heterogeneous growth patterns with a trend towards a progressive increase in size over time [9]. The literature reports that some lesions may grow rapidly, with a doubling time of less than one year, some may grow very slowly, with a doubling time of more than six years, and others may remain stable during follow-up [9]. These different growth patterns were also observed in our study, in which all 33 PSNs in the growing group exhibited different growth rates (Figure 4). An indolent course with a very slow growth rate is most often observed in pure ground-glass nodules (PGGNs) and in PSNs with small solid components [14]. Therefore, surgical resection would not be recommended for all lesions of these SSN subtypes, as most of these SSNs will never become clinically relevant [7; 8]. Moreover, PGGNs and PSNs with small solid components (especially those that are small in size) are often intraoperatively impalpable and indistinguishable from the normal parenchyma [45]; consequently, the localization of these nodules during video or robotic-assisted thoracoscopic surgery is very challenging without the use of a preoperative marking technique [45; 46]. According to the new Fleischner Society guidelines [6], the management of solitary PSNs is mainly based on the size of the solid components, and an aggressive approach is justified only for lesions \begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Independent Variables**} & \multicolumn{2}{c}{**PSN Outcome**} & \multicolumn{1}{c}{\(\chi^{2}\) **Test**} \\ \cline{2-4}  & **Growing (\(n\) = 33)** & **Nongrowing (\(n\) = 17)** & \(p\) **Value** \\ \hline Smoking history & & & \\ No & 7 (14) & 8 (16) & 0.061 \\ Yes & 26 (52) & 9 (18) & \\ \hline Oncologic history & & & \\ No & 13 (26) & 14 (28) & 0.004 \\ Yes & 20 (40) & 3 (6) & \\ \hline Emphysema & & & \\ No & 24 (48) & 11 (22) & 0.562 \\ Yes & 9 (18) & 6 (12) & \\ \hline Lobe location & & & \\ Middle/lower & 10 (20) & 8 (16) & 0.247 \\ Upper & 23 (46) & 9 (18) & \\ \hline \hline \end{tabular} Data are presented as the number (percentage).  
\end{table} 
Table 4: _Cont._with solid components \(\geq\)6 mm. As a result, for PSNs with a solid component \(<\)6 mm, conservative management is recommended [6; 14]. From this point of view, appropriate knowledge about the growth patterns of solitary PSNs with small solid components is an important issue in lung cancer screening and in clinical practice. The translation of morphological analysis from a visual to computerized assessment seems to be very promising for the management of SSNs, as this approach may help to predict the behavior of these nodules and consequently aid in the early detection of surgical and nonsurgical nodules.