P2D324: Measuring the Impact of Vacuum Bell Therapy on Pectus Excavatum Using White Light Scanning

Background: The Haller Index (HI) as derived from chest radiography (CXR) or computed tomography (CT) has been the standard for measuring severity in pectus excavatum (PE). Alternative methods of optical scanning to measure the severity of pectus deformities may reduce exposure to ionizing radiation and allow repeat measurements to assess response to therapy.. This study assessed the reliability of a handheld 3D White Light Scanner (WLS) in a clinic setting to obtain external chest wall measurements, including indicators of PE severity and patient response to nonoperative vacuum bell therapy.

Methods: White light scans were performed and data collected prospectively from pediatric patients with PE who were prescribed vacuum bell therapy at a single institution starting in April 2022. Prior to initiating therapy, a WLS-derived “external” Haller index (WLS_EHI) was calculated by dividing the mediolateral diameter by the anteroposterior diameter of a cross-section through the chest at the deepest point of PE depression. A novel WLS-derived maximal funnel depth (WLS_FD) was calculated as the distance between the deepest point of the depression and a coronal plane across the most anterior portion of the chest (Figure 1). Pearson regression analysis assessed correlation between CXR-derived HI, physician-measured Pectus Excavatum Depth (PED), and WLS_FD. Manual and WLS chest measurements were repeated at each follow-up visit and compared to baseline.

Results: Forty-four patients with PE initiated vacuum bell therapy and were scanned with WLS. The cohort consisted of 38 males (86%), had a median age of 14 years (IQR 13-15), and BMI of 18.4 (IQR 17.3-19.9). Developing breast tissue in four female patients precluded calculation of WLS_FD. For 42 patients with complete baseline imaging, WLS_EHI correlated with HI (r = 0.42, p=0.006) and PED (r = 0.58, p< 0.0001). Notably, baseline WLS_FD demonstrated strong correlation with PED (r = 0.95, p< 0.0001); these correlations are shown in Figure 2.

Seven patients had both baseline and follow-up chest wall measurements at an average follow-up of 5.7 months. All patients had stable or improved PE defects, as measured by PED. On average, patients had a 10% decrease in their PED, corresponding to a 0.26 cm decrease in PED. This corresponded to an 8% decrease in WLS_FD, or a 1.76 mm decrease in PED. Percent change in PED also strongly correlated with percent change in WLS_FD (r = 0.89, p = 0.007).

Conclusion: Our current data suggest that WLS is a feasible means of objectively quantifying the severity of PE deformities and reliably monitoring defect progression in response to vacuum bell therapy. A WLS-derived maximal funnel depth best correlates with physician-measured PED, while WLS_EHI less strongly correlates with PED and HI.