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External Severity Indices for Quantifying Pectus Excavatum Validated Using Pre- and Postoperative CT Analysis

Mohammad F. Obeid¹, Nahom Kidane¹, Qi Zeng², Chenghao Chen², Robert E. Kelly³, Frederic D. McKenzie¹

¹Modeling, Simulation, and Visualization Eng. Dept., Old Dominion University, USA

²Pediatric Thoracic Surgery, Beijing Children's Hospital, China

³Pediatric Surgery, Children’s Hospital of The King’s Daughters and Eastern Virginia Medical School, USA

 

Background: Studies have shown that the value of Haller index (HI), unlike that of the correction index (CI), is very reliant on chest width, which may misrepresent pectus excavatum (PE) severity especially for postoperative assessment. In this work, we demonstrate the opportunity of utilizing external surface profiles of the chest, generated from CT-data or from optical scanning, to propose severity indices.

Patients and Methods: Pre- and postoperative CT scan data for 30 Nuss procedure patients was obtained from the Beijing Children's Hospital and classical Haller and correction indices were calculated. To hypothesize a method where CT scans are not required to evaluate PE severity, an external Haller index (XHI) was calculated using skin surfaces. Furthermore, we calculate a proposed external correction index (XCI) by computing the percent difference between the distance from the most anterior external skin margin of the chest wall to the line placed at the patient’s back; and that from the most depressed skin margin.

Results: Mean preoperative HI and CI values exceed recommended thresholds for surgery [2, 4] for all patients (6.15±3.11 and 50%±13%, respectively). Mean preoperative external indices show similar trends with 1.94±0.16 for XHI and 19%±4% for XCI. For statistical analysis, Pearson's correlation was evaluated between HI and XHI resulting with 0.81 (p < 0.01) for preoperative data and 0.90 (p < 0.01) for postoperative data. Similarly, a consistent correlation was found between CI and XCI with 0.91 (p < 0.01) for preoperative data and 0.93 (p < 0.01) for postoperative data. Using linear regression, external counterparts of the standard 3.25 HI and 28% CI severity cut-off points were evaluated as 1.75 and 10.5%, respectively. As suspected, since HI and XHI are highly correlated, XHI displayed unreliability for postoperative assessment as 40% of patients reflect postoperative values above the calculated XHI severity threshold of 1.75.

Conclusion: We proposed an externally measured index (XCI) to quantify PE pre- and postoperatively without the need for CT. A recommended severity cut-off value of 10.5% was determined.

Keywords: Pectus excavatum, severity measurement, correction index.