Comparison of Chest Radiography and Computed Tomography in Haller Index Calculation for Pectus Excavatum Evaluation

Pectus excavatum (PE) is thought to be the most common anterior chest wall malformation (1). It is a depression of the sternum in a funnel shape which leads to different cardiopulmonary complications in severe cases (2). It is estimated that 65 to 95 percent of all congenital chest wall deformities are caused by PE; the incidence of PE has been published to be 8 in every 1000 live births (3). If affected, patients tend to be tall with pot-bellied appearance and forward drifting shoulders. More severe forms of PE are accompanied by leftward displacement of the heart, imprint on the sternum of the right atrium and right ventricle, and lead to diastolic dysfunction (4).

 Causes of symptoms due to the deformity disproportionately increase with age following a progressive remodeling of thoracic cage. If the PE is severe, then surgical treatments such as open or Ravitch procedure and minimally invasive Nuss procedure (5) will be indicated. The diagnosis and the degree of seriousness of PE should be determined prior to surgery by a radiological examination even if it involves chest X-rays or computed tomography (CT) (6) (7). One of these radiologic methods is the Haller Index which measures the extent of PE based upon the chest circumference at the most severe point of the deformity, whereby a threshold of ≥ 3.2 will categorize the PE as severe (7).

 Generally, chest radiography has been suggested as an alternative to CT for providing information required to calculate Haller Index, including reduced exposure to radiation and greater availability; however, CT has traditionally been the test of choice for evaluating and categorizing PE prior to surgery. Several studies have tried to evaluate usefulness, diagnosis accuracy of chest radiography in determining Haller Index (8). Kiani et al. studied the correlation of mean Haller Indices as obtained on chest radiography and CT in a population of 20.2 ± 2.34 years at CMH Peshawar in a cross sectional study with a statistically significant strong positive correlation between the two modalities (9).

 Compared to chest X-ray (0.1 mSv), a whole body CT scan is estimated to provide approximately 10 mSv of radiation exposure, or about 100 times as much. As such, chest radiography may be considered to spare the patient unnecessary radiation exposure and to save cost, as compared to CT. No study pertaining to this objective has been previously done at our hospital and the rationale was to evaluate the usefulness of chest radiography in calculating the Haller Index in the local population to avoid straining healthcare resources and further radiation exposure for the patient.

66 male patients with pectus excavatum were included and alternately allocated to Group A (radiography of the chest) and Group B (computed tomography). The mean age of the study population was 33.6 ± 9.8 years and most of the patients were urban dwelling (71.2%). The demographic characteristics of the study population are presented in Table 1.

Table 1: Demographic characteristics of the study population (n = 66) is provided.

The mean Haller Index calculated on chest radiography (Group A) was 2.01 ± 0.45 which is significantly lower than mean Haller Index calculated on computed tomography (Group B) 2.35 ± 0.39 (independent samples t-test, p<0.001) as shown in Table 2 and Figure 1.

 Table 2: The comparison of Mean Haller Index of Group A and Group B

Figure 1. Compared Mean Haller Index: Chest Radiography (Group A) vs Computed Tomography (Group B).

Based on the CT derived Haller Index cut-off of ≥ 3.2 for severe pectus excavatum, 18.2% (6/33) of the patients in group B had severe disease and 81.8% (27/33) had non-severe disease as shown in Figure 2.

Figure 2. The figure illustrates the severity distribution in CT Group (Group B, 33 patients).

Table 3: The severity classification in computed tomography (Group B, n=33)

This cross sectional comparison demonstrated that there is statistically significant difference between the mean Haller Index determined using chest radiography (2.01 ± 0.45) and using computed tomography (2.35 ± 0.39), (p<0.001). These results compare favorably with the findings of Kiani et al. whereby they found almost identical mean CT derived HL and chest radiography derived HL of 2.35 ± 0.39 vs 2.01 ± 0.45 respectively in a similar population in the city of Peshawar, KP, Pakistan with strong and statistical significant correlation between the two modalities (9).

Similarly, Khanna et al. evaluated patients for pectus excavatum and found correlation between the Haller Index values obtained from chest radiographs and those obtained from CT scans, although the radiographic values were always lower than those of the CT scans, and the two measures were satisfactory for use for screening purposes (8). Ewert et al. also showed that there was a meaningful correlation between external and radiographic chest wall measurements and CT-based measures in patients with chest wall deformities for those with less-radiation measurement methods, allowing for serial measurements (1).

 Part of the explanation for the lessened Haller Index in chest radiography in this study may be the inherent differences between the methods of obtaining images: chest radiography is creating a 2D image of a 3D thoracic cavity, and cross sectional (true-axial) is obtained on CT. However, Messerli-Odermatt et al. investigated a chest X-ray dose-equivalent low-dose CT protocol with tin filtration as a potential compromise between radiation exposure and measurement reliability and concluded that ultra-low dose CT techniques may further reduce this difference and provide significant radiation reduction over current-dose CT (7).

 In a comprehensive review of advances in the imaging of pectus excavatum for preoperative assessment, Coorens et al., noted that although the reference standard for data in definitive surgical assessment is CT, radiation-free options of chest radiography and surface scanning technologies were gradually introduced to screening and follow-up programs, especially in younger patients who would need multiple evaluations (6). This aligns with the result of the present study that even though the absolute Haller Index value was underestimated, it did identify the proportion of patients with clinically relevant deformity (as would be expected based on the CT based severity cut-offs).

 In a population-based cohort study, Biavati et al reported prevalence for radiographic diagnosis of pectus excavatum that were largely consistent with the prevalence of severe cases observed in the current study, as they indicated that the radiographic indices could be useful for epidemiological and screening applications when CT cannot be applied to the entire population (5). Janssen et al also presented a narrative review of pectus excavatum and carinatum, pointing out significant heterogeneity in reported Haller Index values across different imaging modalities and patient populations, thus emphasizing the need for institution-specific comparative data like that of the present study (3).

 This study has certain limitations. It was performed in one tertiary care center and the findings might not be applicable to other centers. Due to the different patients in both groups (A&B) being used, and the same patients not being used under both groups, it was not possible to directly compare them, nor use any diagnostic accuracy parameters like sensitivity or specificity. Further studies of patients with paired measurements and over a broader age range incorporating women may help facilitate a better understanding of the comparative diagnostic performance of chest radiography versus CT.

In patients with pectus excavatum, computed tomography has a mean Haller Index which is higher than the mean index on chest radiography, but the difference is an overall systematic and significant one with a pattern of difference broadly consistent with earlier local and international data. Considering its significantly less radiation exposure and regular ease of availability, the use of chest radiography may be a useful screening tool for pectus excavatum severity with computed tomography reserved in patients who meet or are approaching  surgical threshold.

 ACKNOWLEDGMENT

The authors would like to acknowledge the department of Diagnostic radiology, PNS Shifa Hospital, Karachi for providing institutional support in conducting the study.

 CONFLICT OF INTEREST

None.

 FUNDING

None.

1.      Ewert F, Syed J, Wagner S, Besendoerfer M, Carbon RT, Schulz-Drost S. In patient with chest wall deformity, is there a correlation between an external chest wall measurement and a CT measurement? J Pediatr Surg. 2017;52(10):1583-90.

2.      Boettcher M, Klohs S, Kloth K, Bhullar J, Hempel M, Trah J, et al. Pectus excavatum – epidemiology based on clinical study and review of literature. Eur J Pediatr Surg. 2022;32(04):316-20.

3.      Janssen N, Coorens NA, Franssen AJ, Daemen JH, Michels IL, Hulsewé KW and others. Pectus excavatum and carinatum: epidemiologic, etiopathogenic, clinical and classification aspects in a narrative review. J Thorac Dis. 2024;16(2):1687.

4.      Notrica DM, McMahon LE, Jaroszewski, DE. Pectus disorders (excavatum, carinatum and arcuatum). Adv Pediatr. 2024;71(1):181-94.

5.      Biavati M, Kozlitina J, Alder AC, Foglia R, McColl RW, Peshock RM, et al. Radiographic estimation of chest wall shape in an adult population-based cohort yields a prevalence for pectus excavatum. PLoS One. 2020;15(5):e0232575.

6.      Coorens NA, Janssen N, Daemen JH, Franssen AJ, Hulsewé KW, Vissers YL, et al. Advancements in terms of preoperative imaging of pectus excavatum – a comprehensive review. J Thorac Dis. 2024;16(1):696.

7.      Messerli-Odermatt O, Serrallach B, Gubser M, Leschka S, Bauer RW, Dubois J, et al. Chest X-ray dose equivalent low-dose CT with tin filtration: potential role for the assessment of pectus excavatum. Acad Radiol. 2020;27(5):644-50.

8.      Khanna G.A, Jaju A., Don S, Keys T, Hildebolt CF. Comparison of Haller Index values calculated with chest radiographs versus CT for evaluation of pectus excavatum. Pediatr Radiol. 2010;40(11):1763-7.

9.      Kiani AA, Haider S, Sharif S, tul Kubra K, Fatima K, Murtaza N. Comparison of Haller Index value calculated with Chest Radiograph and computed tomography in evaluation of pectus excavatum. Pak Armed Forces Med J. 2024;74(1):216-19.