Correlation Between Sternal Depression and Cardiac Rotation in Pectus Excavatum: Evaluation With Helical CT

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1 Pediatric Imaging Original Research Chu et al. CT of Pectus Excavatum Pediatric Imaging Original Research Zhi-gang Chu 1 Jian-qun Yu Zhi-gang Yang Li-qing Peng Hong-li Bai Xue-ming Li Chu ZG, Yu JQ, Yang ZG, Peng LQ, Bai HL, Li XM Keywords: CT, heart, lung, pectus excavatum DOI: /AJR Received June 17, 2009; accepted after revision December 23, All authors: Department of Radiology, West China Hospital, Sichuan University, 37 Guo Xue Xiang, Chengdu, Sichuan , China. Address correspondence to J. Q. Yu (cjr.yujianqun@vip.163.com). WEB This is a Web exclusive article. AJR 2010; 195:W76 W X/10/1951 W76 American Roentgen Ray Society Correlation Between Sternal Depression and Cardiac Rotation in Pectus Excavatum: Evaluation With Helical CT OBJECTIVE. The purpose of this study was to investigate the effect of the degree of sternal depression on the cardiac rotation of pectus excavatum as depicted with helical CT. MATERIALS AND METHODS. Sixty-three patients (53 boys, 10 girls; mean age, 9.7 ± 7 years) with pectus excavatum who underwent helical chest CT and surgical correction were included in this study. Depth of sternal depression, CT depression index, cardiac rotation angle, and pulmonary vein angle were measured, and the correlation of these parameters was analyzed. RESULTS. The mean sternal depression was 21 ± 7 mm; CT depression index, 2.7 ± 1.4; cardiac rotation angle, 55 ± 9 ; and pulmonary vein angle, 52 ± 12. The sternal depression (18 mm) in patients with a CT depression index less than 2.4 was less than that in patients with a CT depression index of (sternal depression, 21 mm) or greater than 2.9 (sternal depression, 28 mm) (p < 0.01). Similarly, the cardiac rotation angle (49 ± 5 ) in patients with a CT depression index less than 2.4 was smaller than that in patients with a CT depression index of (55 ± 6 ) or greater than 2.9 (64 ± 12 ) (p < 0.01). The pulmonary vein angle in patients with a CT depression index less than 2.4 (59 ± 11 ) was larger than that in patients with a CT depression index of (50 ± 12 ) or a CT depression index greater than 2.9 (45 ± 8 ) (p < 0.01). Cardiac rotation angle had a positive correlation with CT depression index (r = 0.75, p < 0.01). CONCLUSION. The degree of sternal depression has a positive correlation with the degree of cardiac rotation in pectus excavatum. Helical CT is a valuable technique for evaluating the chest deformity and resultant cardiac rotation. P ectus excavatum is a common deformity of the anterior chest wall. Ninety percent of cases are detected within the first year after birth. This deformity is characterized by posterior curvature of the inferior two thirds of the sternum, usually with the deepest point immediately above the xiphoid. The depression of the anterior chest wall usually decreases the volume of the chest and the lungs and compresses the heart, leading to cardiac morphologic and functional abnormalities and restrictive and obstructive pulmonary disease [1 3]. Most patients experience chest pain that often is fleeting and occurs while the patient is at rest. Pectus excavatum also causes a marked cosmetic defect, which can cause marked changes in a child s behavior and affect quality of life [4]. Surgical correction of pectus excavatum should be considered for both physical and psychologic reasons. In the literature, we found little information on the evaluation of pectus excavatum with helical CT or on the relations between the degree of sternal depression and cardiac shape and function [5 10]. The purpose of this study was to investigate the chest wall deformity and acquired cardiopulmonary changes found with helical CT, especially the effects of sternal depression on cardiac shape and location, in 63 patients who consecutively underwent surgical correction of pectus excavatum. Materials and Methods Patients We collected preoperative helical CT data on 63 patients (53 boys, 10 girls; mean age, 9.7 ± 7 years; range 6 months 22 years) with pectus excavatum who consecutively underwent surgical correction during the 3-year period 2006 through Of the 63 patients, 38 had no clinical symptoms, 13 were susceptible to respiratory tract infections, seven had fatigue, and five had exertional dyspnea. All patients underwent preoperative ECG. In none of the patients was the chest wall deformity due to trauma. W76 AJR:195, July 2010

2 CT of Pectus Excavatum CT Protocol Thirty-five patients underwent 16-MDCT (Somatom Sensation 16 scanner, Siemens Healthcare), and 28 underwent 4-MDCT (Somatom Plus 4 scanner, Siemens Healthcare) of the chest. The scanning parameters were 120 kv; 200 mas; rotation time, 0.5 second; pitch, 1.5; reconstructed section thickness, 8 or 1.5 mm. The patients were in supine position with both hands placed near the head when they underwent the CT examination. Acquisition was performed from the level of the thoracic inlet to immediately inferior to the costophrenic angle. Ten CT examinations were performed with volume-rendering technique, six with multiplanar reconstruction of the bones of the thorax, and nine with surface-shaded display to depict the anterior chest wall deformity. Image Analysis Two senior thoracic radiologists reviewed the image data. Interpretation discrepancy, if any, was resolved by consensus. In the mediastinal window (width, 350 HU; level, 35 HU), the depth of sternal depression and the CT depression index were measured on the slice showing the lowest point of the sternum. Cardiac rotation angle and inferior pulmonary vein angle, however, were measured on the slice with the largest section of left ventricle and left inferior pulmonary vein trunk, respectively. As Figure 1A shows, the depth of sternal depression was the vertical distance between the highest and the lowest points of the anterior chest wall (a). The CT depression index (c/b), used to evaluate the degree of sternal deformity, was the ratio between the maximal internal sagittal diameter of the left side of the chest (c) and the minimal distance between the anterior surface of the vertebral column and the posterior border of the deepest portion of the sternum (b). The cardiac rotation angle, used to evaluate the degree of cardiac rotation, was the angle between the sagittal line (d) from the anterior border of the vertebral body and the line (e) from the anterior border of the vertebral body to the most anterior and most lateral point on the cardiac contour. The inferior pulmonary vein angle, also used to assess cardiac rotation, was the angle between the left inferior pulmonary vein trunk (f) and the midline of the chest (g) (Fig. 1B). The condition of the lungs, such as consolidation, emphysema, and atelectasis, was documented on lung window images (width, 1,200 HU; level, 600 HU). Statistical Analysis Continuous variables were expressed as mean ± SD, and categoric variables were expressed as number and percentage. Analyses were performed with statistical software (SPSS version 13.0 for Windows, SPSS) to compare the degrees of sternal depression (mild, moderate, and severe) and cardiac rotation (cardiac rotation angle, pulmonary vein angle). The rank sum test was performed, and variables were compared. We also evaluated the correlation between CT depression index and cardiac rotation angle. A value of p < 0.05 was considered statistically significant. A Fig. 1 Pectus excavatum. A, Helical CT scan in 15-year-old boy shows measurements of depth of sternal depression (a), CT depression index (c/b), and cardiac rotation angle (curved arrow). d = sagital line from anterior border of vertebral body and line from anterior border of vertebral body (e). B, Helical CT scan in 17-year-old boy shows measurement of pulmonary vein angle (curved arrow). Pulmonary vein for this patient was shown more clearly than for patient in A. f = angle between left inferior pulmonary vein trunk and midline of chest (g). Fig year-old boy with mild sternal depression deformity (CT depression index, 2.0). Helical CT scan shows 15-mm depth of sternal depression and no cardiac rotation or displacement. Fig. 3 6-year-old girl with moderate sternal depression deformity (CT depression index, 2.5) and ECG finding of partial right bundle-branch block. Helical CT scan shows 16-mm depth of sternal depression, heart displacement to left, and slight compression of right ventricle. Results Helical CT Data on the Sternum in Pectus Excavatum The most frequently affected segments of the sternum were the inferior segment of the corpus sterni and the xiphoid process. The average depth of depression of the sternum was 21 ± 7 mm, and the CT depression index was 2.7 ± 1.4. When CT depression index was arbitrarily used to classify the severity of sternal deformity, 30 patients had mild sternal deformity (CT depression index < 2.4) (Fig. 2), 18 patients had moderate sternal deformity (CT depression index, ) (Fig. 3), and 15 patients had severe sternal deformity (CT depression index > 2.9) (Fig. 4). The mean sternal depression depth in each group is shown in Table 1. The differences between the groups were statistically significant (Kruskal-Wallis H = 13.65, p < 0.01). In addition, five patients had sternal obliquity, and 11 had costal cartilage intumescence and nodule formation (Fig. 4A). Effect of Degree of Sternal Depression on the Morphologic Features of the Heart The depressed sternum compressed different chambers of the heart, including the right ventricle (33 cases), the right atrium (11 cases), the left atrium (five cases), and the left ventricle (two cases). The average cardiac rotation angle was 54.9 ± 9.5 to the left, and the average pulmonary vein angle was 53.0 ± The cardiac rotation angles and pulmonary vein angles of mild, moderate, and severe sternal deformities are summarized in Table 1. Both of these parameters exhibited B AJR:195, July 2010 W77

3 Chu et al. tients), emphysema of the left lower lobe in seven patients (26%), and congenital bullae in one patient (4%). The patients with moderate or severe deformity had different degrees of abnormal inflation in the left lower field. A C Fig year-old woman with severe sternal depression deformity (CT depression index, 8.3) and multiple episodes of cough and fever. A, Helical CT scan shows 35-mm depth of sternal depression and complete shift of heart into left thoracic cavity. Depressed sternum is rotated slightly and accompanied by intumescent costal cartilage. B, CT scan of chest obtained with lung window shows scattered small areas of patchy consolidation in basal segment of inferior lobe of left lung. C, Volume-rendered image shows sternum depressed backward and slightly inclined. D, Sagittal multiplanar reconstruction image shows corpus sterni bending backward. statistically significant differences between groups (cardiac rotation angle, H = 24.46, p < 0.01; pulmonary vein angle, H = 13.54, p < 0.01). As the CT depression index increased, the cardiac rotation angle increased with a correlation coefficient of 0.75 (Fig. 5). ECG and Pulmonary Abnormalities in Pectus Excavatum ECG abnormalities were found in 28 patients (44%) and pulmonary abnormalities in 27 patients (43%). The ECG abnormalities were partial right bundle-branch block in 15 patients (54%), T-wave alteration with counterclockwise rotation in eight patients (29%), premature atrial beats in four patients (14%), and pulmonary P-wave and inferior wall myocardial ischemia in one patient (4%). The pulmonary abnormalities included pulmonary consolidation in 19 patients (70%) (inferior lobes of both lungs, 10 patients; right middle lobe, four patients; lingula, five pa- TABLE 1: Relation Between Cardiopulmonary Abnormalities and Degree of Deformity B D Discussion Pectus excavatum is the most common type of congenital chest wall abnormality. The morbidity is %, and boys are affected approximately four times as often as girls [5, 6]. This condition is typically noticed at birth, and most cases are diagnosed within the first year after birth. The deformity also can be acquired, resulting from chronic lung disease, neuromuscular disease, and trauma [11]. Worsening of the appearance of the chest and the onset of symptoms usually are reported during rapid bone growth in the early teenage years. However, the degree of deformity does not increase with age and has no relation to sex. Because the inferior mediastinum is anterior to the body of the sternum and the thoracic vertebrae are posterior to it, the space between is relatively fixed. When the sternum is depressed, the volume of this space decreases, pulmonary movement is restricted, and the anatomic relations of the airway, heart, and adjacent structures are altered. These effects can result in ventilatory and cardiovascular impairment. Therefore, patients with pectus excavatum usually have expiratory dyspnea, restrictive pulmonary disease, chest pain, reduction in exercise capacity, and arrhythmia [1, 2, 12, 13]. It has been assumed [14] that the degree of physiologic impairment is related to the severity of the deformity. As our results show, patients with moderate and severe sternal deformity were more prone to clinically significant manifestations. The inferior segment of the sternum and xiphoid process can be depressed to different degrees in different patients with pectus excavatum, the depression varying from mild to very severe. The lower portion of thorax may have the appearance of a symmetric dumbbell on transverse CT images, Parameter Mild Deformity (n = 30) Moderate Deformity (n = 18) Severe Deformity (n = 15) All Patients (n = 63) p Sternal depression (mm) 18 ± 5 21 ± 6 28 ± 8 21 ± 7 < 0.01 Cardiac rotation angle ( o ) 49 ± 5 55 ± 6 64 ± ± 9 < 0.01 Pulmonary vein angle ( o ) 59 ± ± ± 8 52 ± 12 < 0.01 No. of ECG abnormalities 7 (23) 10 (56) 11 (73) 28 (44) No. of cases of pulmonary change 6 (20) 11 (61) 10 (67) 27 (43) Note Data are number with percentage in parentheses or mean ± SD. The CT depression indexes for mild, moderate, and severe deformity of sternum are < 2.4, , and > 2.9. Dash [ ] indicates not applicable. W78 AJR:195, July 2010

4 CT of Pectus Excavatum CT Depression Index Cardiac Rotation Angle ( ) Fig. 5 Graph shows positive correlation between CT depression index and cardiac rotation angle (r = 0.75, p < 0.01). but asymmetric deformity is more common, usually because of the slight rotation of the sternum and asymmetric intumescence of the costal cartilage. Helical CT images with 3D reconstruction more clearly show the deformity whereby the inferior segment of the sternum bends obliquely backward. The heart is situated between the sternum and the vertebral column with the right ventricle in the midline adjacent to the sternum. Therefore, the right ventricle is the chamber most vulnerable to being shifted and compressed in pectus excavatum, followed by the right atrium. Of the 63 patients in this study, 33 had a compressed right ventricle that manifested flattening and even slight depression of the anterior ventricular wall. The depressed sternum can compress the heart directly, rotate it to the left, and even displace it. The deeper the sternal depression and the larger the CT depression index, the more pronounced is the cardiac rotation. In our study, a mild degree of sternal depression caused no significant compression of the heart, but moderate and severe sternal depression caused the heart to move to the left and even completely into the left thoracic cavity accompanied by cardiac rotation. The angle of cardiac rotation can be an indicator of the positional change of the heart, reflecting the degree of sternal depression and its effects on the heart. The depressed sternum can restrict the heart directly, resulting in not only compression of the right ventricle but also myocardial ischemia, which leads to ECG abnormalities, especially partial right bundle-branch block [8, 12, 13]. Fourteen of the 63 patients in this study had partial right bundle-branch block, and eight had T-wave changes and counterclockwise rotation. Among the patients with cardiac abnormalities, abnormal ECG findings were more common in those with more severe sternal depression. Deformities of the inferior thorax can indirectly affect mechanical ventilation of the airways in pectus excavatum [1, 2]. Moreover, displacement and rotation of the heart caused by the depressed sternum can compress basal vessels and the bronchi of the inferior lobe of the left lung. This abnormality can result in poor ventilation and impaired drainage of secretions in the affected area, increasing the risk of pneumonia. There were 19 cases of pneumonia in our study, including 10 cases of lower lobe pneumonia. In addition, there were seven cases of emphysema, all of which were found in the inferior lobe of the left lung. Although local pulmonary abnormalities are found in some patients, the parameters that reflect the ventilation function of large airways were normal. In this study, comparison of the effects of sternal depression on the heart with the effects on the lungs showed the pulmonary lesions were relatively localized and mild. For patients with severe pectus excavatum, early surgical correction can relieve the structural compression of the chest to allow normal growth, prevent pulmonary and cardiac dysfunction in adolescence and adulthood, and ameliorate the cosmetic effect of the deformity [15]. The minimally invasive Nuss [16] technique has become widely accepted, because it is safe and successful in the management of pectus excavatum. Preoperative knowledge of the degree of sternal depression, symmetry of the thorax, and cardiac and pulmonary conditions is critical for the success of this procedure. Although some postoperative studies [17, 18] have shown no significant and objective improvement in pulmonary function, other reports [11, 19] have shown improvement in cardiovascular function after the repair. Therefore, surgical repair of pectus excavatum does have physiologic benefits besides correction of the deformity. Several imaging techniques can be used for the preoperative evaluation of pectus excavatum. Chest radiographic findings readily confirm the presence of the pectus deformity and can be used to calculate the Haller index, but yield little information about the thoracic bones and intrathoracic organs. Chest MRI can be used for precise measurement of the degree of sternal depression and assessment of cardiac conditions, but it is limited in displaying bones and the lungs. MRI also is time-consuming, and image quality can be suboptimal in examinations of uncooperative children [20]. Compared with radiography and MRI, chest CT has advantages in preoperative evaluation. First, the severity of the deformity can by objectively assessed, the intrathoracic organs can be located exactly, and the shape of the thoracic bones can be determined with 3D reconstruction techniques (surface-shaded display, multiplanar reformation, and volume rendering). The CT findings have direct implications in selection of the type of repair and equipment used, especially for patients who undergo minimally invasive surgical repair. The second advantage of CT is that the pulmonary abnormalities associated with the chest deformity can be detected. There were two limitations to this study. First, cardiac shape was not evaluated with objective indexes. Second, preoperative and postoperative indexes were not compared because postoperative data were not available owing to the length of time required to complete the Nuss procedure (~ 2 years for children and 3 or 4 years for adults) [10]; because of concern about radiation dose, especially for children; and because clinicians usually select chest radiography for follow-up imaging to verify the proper alignment of the bar used in the repair. Further study is needed to overcome the limitations. This study showed that in pectus excavatum the degree of sternal depression has a positive correlation with cardiac rotation and that helical CT is a valuable technique for adequate evaluation of the thoracic and cardiac abnormalities. The CT findings are potentially useful in decisions about surgical repair of this condition. References 1. Donnelly LF, Bisset GS 3rd. Airway compression in children with abnormal thoracic configuration. AJR:195, July 2010 W79

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