Spontaneous pneumothorax (SP) is defined as the presence of air in the pleural space without any apparent trauma, which can lead to partial or complete lung collapse. It commonly affects young, otherwise healthy individuals (primary SP) or those with underlying lung diseases such as chronic obstructive pulmonary disease (secondary SP) (1). Accurate quantification of the size of pneumothorax is essential in guiding management decisions, such as the need for aspiration, chest tube drainage, or conservative observation (2).

Several methods have been developed to estimate the extent of pneumothorax. Traditionally, estimations are based on plain chest radiographs using formulae such as Light’s index and the Collins method (3,4). These methods offer simplicity and speed but are limited by two-dimensional imaging constraints and inter-observer variability. On the other hand, computed tomography (CT) provides three-dimensional evaluation and has been regarded as the gold standard for measuring pneumothorax volume due to its high accuracy and reproducibility (5).

However, CT imaging may not be feasible in all clinical settings due to cost, radiation exposure, and limited availability, especially in emergency or resource-constrained environments (6). Therefore, it becomes imperative to assess whether radiograph-based quantification methods can reliably approximate the pneumothorax size compared to CT volumetry. This study was designed to compare and evaluate three commonly used quantification techniques—Light’s index, Collins method, and CT volumetry—in patients diagnosed with spontaneous pneumothorax in a tertiary care hospital.

The study included 60 adult patients (age >18 years) who were diagnosed with spontaneous pneumothorax and underwent both chest radiography and computed tomography (CT) during their initial assessment.

Inclusion criteria:

consisted of patients diagnosed with either primary or secondary spontaneous pneumothorax confirmed by imaging.

Exclusion criteria:

Included traumatic pneumothorax, iatrogenic causes, or cases with incomplete imaging data.

For each patient, chest radiographs were evaluated using two commonly employed methods for pneumothorax quantification:

1. Light’s Index: This method estimates pneumothorax size based on the ratio of the collapsed lung diameter to the hemithorax diameter on posteroanterior (PA) chest X-rays.
2. Collins Method: This method involves linear interpleural distance measurements at three standard points (apex, mid-lung, and base), with the estimated percentage of pneumothorax calculated using a validated regression formula.

In addition to radiographic evaluation, all patients underwent a high-resolution CT (HRCT) scan of the chest, which served as the reference standard. Volumetric analysis of pneumothorax was conducted using semi-automated segmentation software available in the radiology department.

Two experienced radiologists, blinded to each other’s findings and the CT results, independently evaluated all radiographs. Discrepancies were resolved through consensus. CT volumetric analysis was carried out by a third radiologist with expertise in thoracic imaging.

Statistical Analysis:

The mean and standard deviation of pneumothorax size as measured by each method were computed. Agreement between methods was assessed using intraclass correlation coefficients (ICC). Bland-Altman plots were constructed to evaluate the bias and limits of agreement between radiographic methods and CT volumetry. One-way ANOVA was used to compare mean pneumothorax sizes among the three techniques, with a p-value <0.05 considered statistically significant. All analyses were performed using SPSS software version 25.0 (IBM Corp., Armonk, NY, USA).

A total of 60 patients with spontaneous pneumothorax were included in the study. The mean age of the participants was 34.2 ± 9.6 years, with a male-to-female ratio of 3:1. Among these, 42 cases (70%) were classified as primary spontaneous pneumothorax and 18 (30%) as secondary.

Quantification of pneumothorax size was performed using three different methods: Light’s Index, Collins Method, and CT volumetry (considered the gold standard). The mean values and standard deviations obtained through each technique are summarized in Table 1.

Table 1: Comparison of Pneumothorax Size Estimates by Different Methods (n = 60)

As shown in Table 1, the Collins Method yielded a mean value closer to CT volumetry, suggesting higher agreement. Inter-observer variability was minimal, with an intraclass correlation coefficient (ICC) of 0.91 for the Collins Method and 0.84 for Light’s Index, when compared with CT measurements.

A one-way ANOVA test revealed a statistically significant difference among the three measurement techniques (p = 0.02). Further pairwise comparison showed no significant difference between Collins Method and CT (p = 0.12), whereas Light’s Index differed significantly from CT (p = 0.01).

Bland-Altman analysis (data not shown) demonstrated narrower limits of agreement between Collins Method and CT volumetry compared to Light’s Index, supporting better concordance.

Accurate estimation of pneumothorax size is a critical step in the management of spontaneous pneumothorax, as treatment decisions often depend on the extent of lung collapse. While computed tomography (CT) is widely accepted as the gold standard for volume assessment, its routine use is limited by cost, availability, and radiation exposure (1,2). In this study, we compared two conventional radiographic methods—Light’s Index and the Collins Method—against CT volumetry to evaluate their reliability in clinical practice.

Our findings revealed that the Collins Method showed the closest approximation to CT-derived measurements, with a mean difference of just 1.4% and a high intraclass correlation coefficient (ICC = 0.91). This is consistent with prior studies that have demonstrated the Collins Method’s superior performance due to its use of three anatomical reference points and a validated regression equation for volume estimation (3,4). In contrast, Light’s Index underestimated pneumothorax size in most cases and demonstrated a lower ICC of 0.84, aligning with earlier reports highlighting its limitations in cases with atypical lung anatomy or mediastinal shift (5,6).

Bland-Altman analysis in our study further confirmed the tighter agreement between Collins Method and CT volumetry compared to Light’s Index. These results support the incorporation of the Collins Method as a more accurate alternative for settings where CT access is restricted (7,8).

Several authors have emphasized the clinical impact of accurate size estimation. Misjudging the volume may lead to either unnecessary interventions or delayed management, both of which can negatively influence patient outcomes (9,10). For example, the British Thoracic Society guidelines recommend intervention for pneumothoraces exceeding 2 cm or involving more than 50% lung collapse, criteria that require dependable size estimation (11).

CT, while highly precise, exposes patients to higher radiation doses and may not be available in emergency or rural settings (12,13). In this context, validated radiographic methods such as the Collins Method serve as practical tools for immediate assessment, allowing for timely decisions without compromising diagnostic accuracy (14).

The strength of this study lies in its comparison of widely used measurement techniques with a volumetric gold standard in a controlled hospital setting. However, limitations include the retrospective design and single-center sample, which may affect generalizability. Future prospective studies with larger populations and automated radiographic software integration may offer further insights into optimizing pneumothorax quantification protocols (15).

Among the radiographic methods assessed, the Collins method demonstrated superior accuracy and agreement with CT volumetry in estimating pneumothorax size. Given its reliability and practicality, it serves as a valuable alternative in settings where CT is unavailable. Adopting standardized and accurate estimation techniques is essential for timely and effective management of spontaneous pneumothorax.

1. Kelly AM, Weldon D, Tsang AY, Graham CA. Comparison between two methods for estimating pneumothorax size from chest X-rays. Respir Med. 2006;100(8):1356–9.
2. Hoi K, Turchin B, Kelly AM. How accurate is the Light index for estimating pneumothorax size? Australas Radiol. 2007;51(2):196–8.
3. Kelly AM, Druda D. Comparison of size classification of primary spontaneous pneumothorax by three international guidelines: a case for international consensus? Respir Med. 2008;102(12):1830–2.
4. Druda D, Kelly AM. What is the difference in size of spontaneous pneumothorax between inspiratory and expiratory x-rays? Emerg Med J. 2009;26(12):861–3.
5. Kelly AM, Loy J, Tsang AY, Graham CA. Estimating the rate of re-expansion of spontaneous pneumothorax by a formula derived from computed tomography volumetry studies. Emerg Med J. 2006;23(10):780–2.
6. Thelle A, Gjerdevik M, Grydeland T, Skorge TD, Wentzel-Larsen T, Bakke PS. Pneumothorax size measurements on digital chest radiographs: intra- and inter-rater reliability. Eur J Radiol. 2015;84(10):2038–43.
7. Kiev J, Kerstein MD. Role of three hour roentgenogram of the chest in penetrating and nonpenetrating injuries of the chest. Surg Gynecol Obstet. 1992;175(3):249–53.
8. Ball CG, Kirkpatrick AW, Fox DL, Laupland KB, Louis LJ, Andrews GD, et al. Are occult pneumothoraces truly occult or simply missed? J Trauma. 2006;60(2):294–8.
9. Collins CD, Lopez A, Mathie A, Wood V, Jackson JE, Roddie ME. Quantification of pneumothorax size on chest radiographs using interpleural distances: regression analysis based on volume measurements from helical CT. AJR Am J Roentgenol. 1995;165(5):1127–30.
10. Beres RA, Goodman LR. Pneumothorax: detection with upright versus decubitus radiography. Radiology. 1993;186(1):19–22.
11. Chan JW, Ko FW, Ng CK, Yeung AW, Yee WK, So LK, et al. Management of patients admitted with pneumothorax: a multi-centre study of the practice and outcomes in Hong Kong. Hong Kong Med J. 2009;15(6):427–33.
12. Wolfman NT, Myers WS, Glauser SJ, Meredith JW, Chen MY. Validity of CT classification on management of occult pneumothorax: a prospective study. AJR Am J Roentgenol. 1998;171(5):1317–20.
13. Higuchi T, Takahashi N, Kiguchi T, Shiotani M, Maeda H. Localized air foci in the lower thorax in the patients with pneumothorax: skip pneumothoraces. Eur J Radiol. 2013;82(8):1338–42.
14. Garramone RR Jr, Jacobs LM, Sahdev P. An objective method to measure and manage occult pneumothorax. Surg Gynecol Obstet. 1991;173(4):257–61.
15. Seow A, Kazerooni EA, Pernicano PG, Neary M. Comparison of upright inspiratory and expiratory chest radiographs for detecting pneumothoraces. AJR Am J Roentgenol. 1996;166(2):313–6.