Pectus Excavatum: Current Imaging Techniques and Opportunities for Dose Reduction

Mini thoracic CT adequately determines Haller index and decreases radiation exposure in children with pectus excavatum

INTRODUCTION

The preoperative assessment of Pectus Excavatum (PE) is resource intensive. CT chest for the purpose of calculating a Haller index (HI) remains a central component and is necessary for third-party reimbursment for surgical correction. With the goal of minimizing radiation exposure, a strategy was introduced to perform a mini-Thoracic CT (mini-CT) for the calculation of HI.

OPERATIVE TECHNIQUE

The mini-CT was performed as follows: a radio-opaque marker (ROM) was placed at the clinical deepest point of the deformity. The CT was then columnated to scan 3 cm above and 3 cm below the ROM. HI was calculated according to previously described technique. Seven children with PE who underwent mini-CT were age and weight matched to 7 children with PE who underwent standard low dose CT chest during the same time period. Radiation doses were evaluated using dose length product (DLP) and effective dose (mSv) between the two groups. Significance of differences was determined using the students t-test. The DLP of mini-CT compared to chest-CT was 17.9 vs 48.9,mGycm respectively. (p< 0.001) The mSv of the mini-CT compared to chest-CT was 0.32 vs 0.88, sMV respectively. (p<0.001) Both DLP and mSv were reduced by 63% in children who received a mini-CT. All children obtained insurance authorization and underwent uncomplicated Nuss repair.

CONCLUSION

For children with pectus excavatum deformities the mini-Thoracic CT is an effective method to calculate the HI. Compard to the conventional low dose chest CT, the mini-CT strategy significantly reduces radiation exposure to the child by 63% with no impact on third-party authorizations or Nuss repair.

A new tool for assessing Pectus Excavatum by a semi-automatic image processing pipeline calculating the classical severity indexes and a new marker: the Volumetric Correction Index

Background

In clinical assessment of Pectus Excavatum (PE), the indication to surgery is based not only on symptoms but also on quantitative markers calculated from Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scans. According to clinical routine, these indexes are measured manually by radiologists with limited computer support. This process is time consuming and potentially subjected to inaccuracy and individual variability in measurements. Moreover, the existing indexes have limitations, since they are based on linear measurements performed on single slices rather than on volumetric data derived from all the thoracic scans.

Results

In this paper we present an image processing pipeline aimed at providing radiologists with a computer-aid tool in support of diagnosis of PE patients developed in MATLAB® and conceived for MRI images. This framework has a dual purpose: (i) to automatize computation of clinical indexes with a view to ease and standardize pre-operative evaluation; (ii) to propose a new marker of pathological severity based on volumetric analysis and overcoming the limitations of existing axial slice-based indexes. Final designed framework is semi-automatic, requiring some user interventions at crucial steps: this is realized through a Graphical User Interface (GUI) that simplifies the interaction between the user and the tools. We tested our pipeline on 50 pediatric patients from Gaslini Children’s Hospital and performed manual computation of indexes, comparing the results between the proposed tool and gold-standard clinical practice. Automatic indexes provided by our algorithm have shown good agreement with manual measurements by two independent readers. Moreover, the new proposed Volumetric Correction Index (VCI) has exhibited good correlation with standardized markers of pathological severity, proving to be a potential innovative tool for diagnosis, treatment, and follow-up.

Conclusions

Our pipeline represents an innovative image processing in PE evaluation, based on MRI images (radiation-free) and providing the clinician with a quick and accurate tool for automatically calculating the classical PE severity indexes and a new more comprehensive marker: the Volumetric Correction Index.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12880-022-00754-0.

What Can Proton Beam Therapy Achieve for Patients with Pectus Excavatum Requiring Left Breast, Axilla and Internal Mammary Nodal Radiotherapy?

AIMS

Exposure of the heart to radiation increases the risk of ischaemic heart disease, proportionate to the mean heart dose (MHD). Radiotherapy techniques including proton beam therapy (PBT) can reduce MHD. The aims of this study were to quantify the MHD reduction achievable by PBT compared with volumetric modulated arc therapy in breath hold (VMAT-BH) in patients with pectus excavatum (PEx), to identify an anatomical metric from a computed tomography scan that might indicate which patients will achieve the greatest MHD reductions from PBT.

MATERIALS AND METHODS

Sixteen patients with PEx (Haller Index ≥2.7) were identified from radiotherapy planning computed tomography images. Left breast/chest wall, axilla (I-IV) and internal mammary node (IMN) volumes were delineated. VMAT and PBT plans were prepared, all satisfying target coverage constraints. Signed-rank comparisons of techniques were undertaken for the mean dose to the heart, ipsilateral lung and contralateral breast. Spearman's rho correlations were calculated for anatomical metrics against MHD reduction achieved by PBT.

RESULTS

The mean MHD for VMAT-BH plans was 4.1 Gy compared with 0.7 Gy for PBT plans. PBT reduced MHD by an average of 3.4 Gy (range 2.8-4.4 Gy) compared with VMAT-BH (P < 0.001). PBT significantly reduced the mean dose to the ipsilateral lung (4.7 Gy, P < 0.001) and contralateral breast (2.7 Gy, P < 0.001). The distance (mm) at the most inferomedial extent of IMN volume (IMN to heart distance) negatively correlated with MHD reduction achieved by PBT (Spearman's rho -0.88 (95% confidence interval -0.96 to -0.67, P < 0.001)).

CONCLUSION

For patients with PEx requiring left-sided breast and IMN radiotherapy, a clinically significant MHD reduction is achievable using PBT, compared with the optimal photon technique (VMAT-BH). This is a patient group in whom PBT could have the greatest benefit.

Does chest wall conformation influence myocardial strain parameters in infants with pectus excavatum?

PURPOSE

To investigate the possible influence of chest wall conformation on myocardial strain parameters in a consecutive population of infants with pectus excavatum (PE), noninvasively assessed by modified Haller index (MHI).

METHODS

Sixteen consecutive PE infants (MHI >2.5) and 44 infants with normal chest shape (MHI ≤2.5) entered in this prospective case-control study. All infants underwent evaluation by neonatologist, transthoracic echocardiography implemented with two-dimensional speckle tracking echocardiography (2D-STE) analysis of both ventricles and MHI assessment (ratio of chest transverse diameter over the distance between sternum and spine), at two time points: within 3 days and at about 40 days of life.

RESULTS

At 2.1 ± 1 days of life, compared to controls (MHI = 2.01 ± 0.2), PE infants (MHI = 2.76 ± 0.2) were diagnosed with significantly smaller cardiac chambers dimensions. Biventricular contractile function and hemodynamics were similar in both groups of infants. Left ventricular (LV) global longitudinal strain (GLS) (-16.0 ± 2.8 vs. -21.7 ± 2.2%), LV-global circumferential strain (GCS) (-16.3 ± 2.7 vs. -24.0 ± 5.2%), LV-global radial strain (GRS) (24.2 ± 3.0 vs. 31.5 ± 6.3%), and right ventricular free wall longitudinal strain (RVFWLS) (-16.0 ± 3.2 vs. -22.3 ± 4.4%) were significantly reduced in PE infants versus controls (all p < 0.001). A strong inverse correlation between MHI and the following parameters: LV-GLS (r = -0.92), LV-GCS (r = -0.88), LV-GRS (r = -0.87), and RVFWLS (r = -0.88), was demonstrated in PE infants, but not in controls, in perinatal period (all p < 0.001). Analogous results were obtained at 36.8 ± 5.2 days after birth.

CONCLUSIONS

Abnormal chest anatomy progressively impairs myocardial strain parameters in PE infants. This impairment might reflect intraventricular dyssynchrony due to compressive phenomena rather than intrinsic myocardial dysfunction.

Preoperative resource utilization prior to minimally invasive repair of pectus excavatum

BACKGROUND

Preoperative testing to assess the physiologic impact of pectus excavatum is sometimes ordered to meet third-party payor preauthorization requirements. This study describes the utility of physiologic testing prior to minimally invasive repair of pectus excavatum (MIRPE).

METHODS

We retrospectively reviewed patients that underwent MIRPE from 1/2012-7/2016 at two academic children's hospitals. Data collected included demographics, insurance, Haller Index (HI), pulmonary function tests (PFTs) and echocardiograms (ECHO) obtained, and preauthorization denials.

RESULTS

A total of 360 patients (mean age 15.7 ± 2.0 years; mean HI 4.5 ± 1.5) underwent MIRPE (Hospital 1: 189, Hospital 2: 171). Commercial insurers covered 84% of patients. Hospital 1 obtained more frequent preoperative testing (PFTs: 73% vs 6%, p < 0.0001). Overall, 72% of PFTs were normal with abnormal studies limited to mild findings. Similarly, 85% of ECHOs were normal. Third-party payors more frequently denied preauthorization for MIRPE at Hospital 2 (11% vs. 5%, p = 0.03).

CONCLUSIONS

More frequent preoperative testing may decrease initial preauthorization denials for MIRPE; however, this increased utilization of resources may not be necessary as the majority of test results are normal.

Computer-aided diagnosis of pectus excavatum using CT images and deep learning methods

Pectus excavatum (PE) is one of the most common chest wall defects. Accurate assessment of PE deformities is critical for effective surgical intervention. Index-based evaluations have become the standard for objectively estimating PE, however, these indexes cannot represent the whole information of chest CT images and may associated with significant error due to the individual differences. To overcome these limitations, this paper developed a computer-aided diagnosis (CAD) system based on the convolutional neural network (CNN) to automatically learn discriminative features and classify PE images. We also adopted block-wise fine-tuning methods based on the transfer learning strategy to reduce the potential risk of overfitting caused by limited data and experimentally explored the best fine-tuning degree. Our method achieved a high level of classification accuracy with 94.76% for PE diagnosis. Furthermore, we proposed a majority rule-based voting method to provide a comprehensively diagnostic results for each patient, which integrated the classification results of the whole thorax. The promising results support the feasibility of our proposed CNN-based CAD system for automatic PE diagnosis, which paves a way for comprehensive assessments of PE in clinics.

Outpatient monitoring of Pectus Excavatum: a Neural Network-based approach

Pectus Excavatum (PE) is a congenital anomaly of the ribcage, at the level of the sterno-costal plane, which consists of an inward angle of the sternum, in the direction of the spine. PE is the most common of all thoracic malformations, with an incidence of 1 in 300-400 people. To monitor the progress of the pathology, severity indices, or thoracic indices, have been used over the years. Among these indices, recent studies focus on the calculation of optical measures, calculated on the optical scan of the patient's chest, which can be very accurate without exposing the patient to invasive treatments such as CT scans. In this work, data from a sample of PE patients and corresponding doctors' severity assessments have been collected and used to create a decision tool to automatically assign a severity value to the patient. The idea is to provide the physician with an objective and easy to use measuring instrument that can be exploited in an outpatient clinic context. Among several classification tools, a Probabilistic Neural Network was chosen for this task for its simple structure and learning mode.

Research progress in the effects of pectus excavatum on cardiac functions

Background

Pectus excavatum, the most common chest wall deformity in children, accounts for nearly 90% of congenital malformations of chest wall. Initially, both parents and doctors paid more attention to the influence of this deformity on patient appearance and psychology. Following deeper studies of pectus excavatum, researchers found that it also affected cardiac functions. The purpose of this review aims to present recent research progress in the effects of pectus excavatum on cardiac functions.

Data sources

Based on aspects of CT, ultrasound cardiography (UCG) and MRI, all the recent literatures on the influence of pectus excavatum on cardiac function were searched and reviewed.

Results

Moderate and severe pectus excavatum did have a negative effect on cardiac function. Cardiac rotation angle, cardiac compression index, right atrial and tricuspid annulus size, septal motion and myocardial strain are relatively effective indexes to evaluate cardiac function.

Conclusions

Pectus excavatum did have a negative effect on cardiac function; so surgeons should actively diagnose and treat such patients in clinical work. However, further research is needed on to explore the measures and indicators that can reflect the changes of cardiac function in patients objectively, accurately, effectively and timely.

Physician-Estimated Depth as a Screening Tool for Computed Tomography Evaluation of Pectus Excavatum

BACKGROUND

Pectus excavatum (PE) is the most common congenital chest wall anomaly with a reported incidence of 1/300 to 1/400 live births and a male predominance. Preoperative evaluation of defect severity typically requires a calculation of the Haller index (HI) and/or correction index (CI) using computed tomography (CT) or x-rays. The purpose of this study was to determine whether physician-estimated depth (PED), a bedside screening tool, could be used to identify a subset of pediatric patients in whom CT was unnecessary.

METHODS

After institutional review board approval (IRB #032018-091), we retrospectively reviewed all patients with a diagnosis of PE between 2009 and 2018 at our academic pediatric center. Demographic information including age, sex, and body mass index were abstracted. Imaging was reviewed to obtain HI and CI and to retrospectively calculate PED. The PED is calculated at the bedside by measuring the depth of the pectus at the site of greatest depression relative to a horizontal surface laid across the deformity. For this retrospective study, we calculated the CT-derived PED by measuring the depth from the horizontal on the respective CT images. Patients without imaging studies and patients with pectus carinatum, arcuatum, or mixed deformities were excluded from this study.

RESULTS

A total of 94 patients met inclusion criteria. Of these, 82% were male, with a median age of 15 y. Patients were further subdivided by BMI, with 46% of patients having a BMI of <18.5 kg/m² (i.e., underweight), whereas 54% of patients had a BMI of ≥18.5 kg/m². Using a threshold PED of 2 cm, patients with a BMI of <18.5 kg/m² had correct classification rates of 93% and 95% using PED relative to HI and CI, respectively. Patients with a BMI of ≥18.5 kg/m² had correct classification rates of 80% and 88% using PED relative to HI and CI, respectively, at the same 2 cm threshold.

CONCLUSIONS

PED is a viable screening tool for the preoperative evaluation of PE with a 2 cm threshold providing the combination of high sensitivity, specificity, and correct classification rates especially in underweight patients.

Optical imaging versus CT and plain radiography to quantify pectus severity: a systematic review and meta-analysis

Background

Computed tomography (CT) and two-view chest radiographies are the most commonly used imaging techniques to quantify the severity of pectus excavatum (PE) and pectus carinatum (PC). Both modalities expose patients to ionizing radiation that should ideally be avoided, especially in pediatric patients. In an effort to diminish this exposure, three-dimensional (3D) optical surface imaging has recently been proposed as an alternative method. To assess its clinical value as a tool to determine pectus severity we conducted a systematic review in which we assessed all studies that compared 3D scan-based pectus severity measurements with those derived from CT-scans and radiographies.

Methods

Six scientific databases and three registries were searched through April 30th, 2019. Data regarding the correlation between severity measures was extracted and submitted to meta-analysis using the random-effects model and I²-test for heterogeneity.

Results

Five observational studies were included, enrolling 75 participants in total. Pooled analysis of participants with PE demonstrated a high positive correlation coefficient of 0.89 [95% confidence interval (CI): 0.81 to 0.93; P<0.001] between the CT-derived Haller index (HI) and its 3D scan equivalent based on external measures. No heterogeneity was detected (I²=0.00%; P=0.834).

Conclusions

3D optical surface scanning is an attractive and promising imaging technique to determine the severity of PE without exposure to ionizing radiation. However, further research is needed to determine novel cut-off values for 3D scans to facilitate clinical decision making and help determine surgical candidacy. No evidence was found that supports nor discards the use of 3D scans to determine PC severity.

A novel technique to measure severity of pediatric pectus excavatum using white light scanning

BACKGROUND/PURPOSE

Computed tomography (CT) derived Haller Index (HI) remains the standard for quantifying severity in patient with pectus excavatum (PE). Optical scanning described in literature reports optimistic results and new indices that correlate with HI. This study assessed the feasibility of a handheld White Light Scanner (WLS) to obtain 3D measurements and indices of PE deformity.

METHODS

From April 2015-April 2017, WLS scanning was conducted by orthotists during clinical visits. Included were children with PE up to 18 years. Analysis assessed correlation of a WLS-derived severity index, Hebal-Malas Index (HMI), with physician measured PE Depth (PED), and CT-derived HI.

RESULTS

Of 195 participants, 185(94%) patients with PE were scanned and 127(69%) had complete WLS data. For 88 patients undergoing monitoring, HMI correlated with PED (r = 0.42, p = 0.004). For 39 patients with pre-operative CT, HMI demonstrated strong correlation with HI (r = 0.87, p<0.0001).

CONCLUSIONS

WLS demonstrated high feasibility of scanning PE. WLS-derived HMI best correlates with HI for patients with severe pectus deformity. Our current data is suggestive that WLS is best applied for severe deformities and yet to be established for milder deformities. Future yearly WLS will provide data on deformity progression and surgical therapy.

LEVEL OF EVIDENCE

IV.

TYPE OF STUDY

Diagnostic Study.

Is pectus excavatum a risk factor for radiation-induced lung disease in patients undergoing radiation therapy following breast-conserving surgery?

Background

The relationship between radiation dose to the ipsilateral lung and subsequent radiation‐induced lung disease (RILD) in breast cancer patients with pectus excavatum (PE) undergoing radiation therapy (RT) to residual breast tissue after breast‐conserving surgery has not yet been established. The incidence of RILD in such patients with PE, meaning that a large volume of the lung is within the radiation field, has not been determined. Therefore, the aim of this study was to determine the relationship between these factors.

Methods

The study cohort comprised 133 women who underwent three‐dimensional conformal RT to residual breast tissue after breast‐conserving surgery for breast cancer. Diagnoses of PE were based on Haller's, frontosagittal, and Monden's depression indices. Radiation doses to the ipsilateral lung were established from dose‐volume histograms.

Results

Fifty of the 133 participants (37.6%) were diagnosed with RILD; all were asymptomatic. Multivariate analysis revealed a significant correlation between the incidence of RILD and the administration of > 30 Gy (V30). Surprisingly, although patients with PE received higher ipsilateral lung doses, they were less likely to develop RILD than those without PE.

Conclusions

Our data indicate that the incidence of RILD is correlated with the administration of > 30 Gy (V30) and that PE is not a risk factor for RILD after RT to residual breast tissue after breast‐conserving surgery for breast cancer. Surprisingly, individuals with PE may have a lower incidence of RILD than those without this condition.

Recurrence of pectus excavatum following the Nuss procedure

Background

The recurrence of pectus excavatum (PE), in other words, chest wall depression after the completion of repair, is one of the most important issues in PE. However, little about the recurrence of PE is known. The present study aimed (I) to evaluate the characteristics of chest wall depression during treatment and (II) to present the definition of recurrence of PE, investigate the risk factors for recurrence, and predict the recurrence at one year after bar removal (BR).

Methods

Consecutive 99 patients who had undergone BR for PE in a single hospital from March 2012 to June 2017 were included in the present study. Severity of PE is presented as a radiographical Haller index (RHI) in the present study. RHI is calculated by the ratio of the transverse diameter to the anteroposterior (AP) diameter at the point of the deepest chest wall depression. Patients with a ≥3.5 RHI value, which simultaneously increased to more than the value of RHI before BR, were considered as demonstrating recurrence in the present study. Follow-up data after BR were collected at subsequent time points (i.e., immediate before and after, one month, sixth months, and one year after BR). All postoperative chest wall changes were analyzed to find out the difference according to the age at the time of the Nuss procedure (NP) [<10 years old (early group; EG) vs. ≥10 years old (late group, LG)].

Results

The mean age of patients was 8.91 (±5.23) years at the age of the NP and the mean duration of bar placement was 28.4 (±5.04) months. Seventy-eight males and 21 females were included. The pectus type was 79 symmetric and 20 asymmetric cases. The mean observation period after BR was 16.47 (±3.74) months. There was a significant correlation between the Haller index using chest CT and simple radiography data (P<0.001). Irrespective of the age groups, there were a significant decrease in RHI values after the NP (both P<0.001). In addition, there were no differences in RHI values between the EG and the LG cohort before the NP and immediately after the NP (P=0.775, P=0.356, respectively). RHI values was significantly decreased in the EG (P=0.040) and increased without a significance in the LG (P=0.330) during bar placement. The chest wall depression progressed for the first six months after BR. However, the chest wall depression did not progress one year after BR. Recurrence occurred in nine cases at one year after BR (four cases in the EG and five cases in LG). The recurrence rate was higher in the LG than in the EG without a significance (P=0.479). Multivariate analysis of the recurrence revealed that only RHI after the NP was identified as an independent risk factor of the recurrence. ROC study also showed that RHI value after the NP had a significant predictable cutoff value for the recurrence [cutoff value of RHI: 2.91, sensitivity: 88.9%, specificity: 90.0%, P<0.001, area: 0.899, 95% confidence interval (CI): 0.806-0.993].

Conclusions

The present study shows the characteristics of chest wall depression and the risk factor of the recurrence of PE after BR. The effect of the NP is different according to the patient age at the time of the procedure. Early correction of PE can provide better corrective results because of the existence of a more pliable chest wall, which can be easily and sufficiently elevated by the NP. Sufficient elevation of the depressed chest wall should be ensured during the NP to prevent the recurrence of PE.

Nuss Procedure for a Patient with Negative Haller Index

Introduction  Minimally invasive repair for pectus excavatum (MIRPE) is controversial in extremely severe cases of pectus excavatum (PE) and an open repair is usually favored. Our aim is to describe a case of a patient with an extremely severe PE that underwent a minimally invasive approach. Case report  An 8-year-old girl with severe sternum depression was assessed. She had a history of exercise intolerance, nocturnal dyspnea, fatigue, and shortness of breath. Chest computed tomography showed that sternum depression was posterior to the anterior vertebral column; therefore, Haller and correction index could not be measured. Spirometry indicated an obstructive ventilation pattern (forced expiratory volume in 1 second = 74.4%), and echocardiogram revealed a dilated inferior vena cava, mitral valve prolapse with normal ventricular function. After multidisciplinary committee evaluation, a MIRPE approach was performed. All symptoms had disappeared at the 3-month postoperative follow-up; the desired sternum shape was achieved and normalization of cardiopulmonary function was observed. The Nuss bars were removed after a 2-year period. After 18-month follow-up, the patient can carry out normal exercise and is content with the cosmetic result. Conclusion  Nuss procedure is feasible in our 8-year-old patient. In this case, both the Haller and correction index were not useful to assess the severity of PE. Therefore, under these circumstances, other radiologic parameters have to be taken into consideration for patient evaluation.

Pectus Excavatum: A Review of Diagnosis and Current Treatment Options

Osteopathic medicine places a special emphasis on the musculoskeletal system, and understanding how chest wall structure may influence function is critical. Pectus excavatum is a common congenital chest wall defect in which the sternum is depressed posteriorly. Patients may present with complaints of chest wall discomfort, exercise intolerance, and tachycardia. The medical implications, diagnosis, and treatment options for patients with pectus excavatum are reviewed.

Classification of Pectus Excavatum According to Objective Parameters From Chest Computed Tomography

BACKGROUND

Previous classification systems of pectus excavatum have been based on subjective morphologic characteristics. We sought to suggest a new classification system derived from objective variables.

METHODS

Patients who underwent surgical repair of pectus excavatum without a history of previous chest operations were included. Objective morphologic variables were measured from chest computed tomography scan images, and classification was performed by hierarchical clustering of measured indexes. Clinical relevance of the suggested classification was also verified.

RESULTS

Included were 230 patients who underwent operation for pectus excavatum from January 2001 to August 2013. These patients were classified into two major groups: typical (group I; 197 [85.7%]) and atypical (group II; 33 [14.3%]). Group I was further classified into three subgroups according to flatness and symmetry of the chest wall. Group II was further classified into four subgroups according to the severity of sternal torsion and sternal angulation. Two unique types of deformity were identified in group II: the double distortion subgroup (group IIa; 8 [3.5%]) and the reverse torsion subgroup (group IIc; 16 [7.0%]). Scoliosis was more frequently associated with group IIa (p = 0.008).

CONCLUSIONS

Morphologic classification obtained from computed tomography indexes hierarchical clustering identified seven distinct subtypes of pectus excavatum.