A retrospective analysis of haller index and other risk factors in individuals with primary spontaneous pneumothorax

Objective: This study aimed to determine the effects of the Haller Index (HI) and other demographic, clinical, and radiological risk factors in assessing the risk of developing Primary Spontaneous Pneumothorax (PSP). Material and Methods: This retrospective, cross-sectional, case-control study, conducted between 2019 and 2025 at the Thoracic Surgery Clinic of Bolu Abant Izzet Baysal University Training and Research Hospital, included 224 patients diagnosed with PSP and 197 age-matched control individuals (aged 18-35 years). Individuals with a history of secondary spontaneous pneumothorax, traumatic pneumothorax, iatrogenic pneumothorax, congenital pneumothorax, thoracic malignancies, syndromic or genetic diseases were excluded from the study. Demographic and clinical data, such as age, sex, height, weight, Body Mass Index (BMI), and smoking status, along with anteroposterior diameter and lateral diameter measurements, were obtained from the PACS system. The Haller Index was calculated by dividing the lateral diameter by the anteroposterior diameter. Statistical analyses involved the Shapiro-Wilk normality test, followed by the Student's t-test for normally distributed variables, the Mann-Whitney U test for non-normally distributed variables, and the Chi-square test for categorical variables. A multivariate logistic regression analysis was performed to identify independent factors predicting PSP development, and the classification success of the model was evaluated using ROC curves and the Area Under the Curve (AUC) value. Results: Data from a total of 421 individuals (PSP: 224; Control: 197) were analyzed. Individuals in the PSP group were found to be significantly younger (p<0.001), leaner (p<0.001), and taller (p<0.001) compared to the control group. Furthermore, BMI values in the PSP group were also found to be significantly lower (p<0.001). Regarding sex distribution, 84.8% of the PSP group were male (control: 61.4% male, p<0.001), and the rate of smoking was also significantly higher (p<0.001) in the PSP group. In radiological measurements, anteroposterior diameter (p<0.001) and lateral diameter (p<0.001) were significantly larger in the PSP group, while the Haller Index (p<0.005) was significantly lower. In the logistic regression analysis, the lateral diameter (OR=14.88; p<0.0001) was determined to be a significant risk factor for PSP development; whereas age (OR=0.40; p=0.0032), weight (OR=0.13; p<0.0001), and the Haller Index (OR=0.28; p=0.0006) were identified as protective factors. Height, smoking status, and sex did not show a statistically significant effect on PSP development. The predictive performance of the model was high, with an AUC value calculated as 0.89. Conclusion: This study revealed that PSP is more common in young, male individuals with tall stature, low body weight, and low Body Mass Index. A wide lateral diameter was identified as an independent risk factor for PSP development, while age, weight, and the Haller Index were found to have protective effects. These findings suggest that the morphological features of the thoracic structure may play a role in the pathophysiology of PSP, and these demographic and anatomical parameters could provide valuable contributions to identifying individuals predisposed to PSP and personalizing diagnostic and therapeutic processes.