Radiological assessment of children with pectus excavatum
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《美国医学杂志》
1 Department of Pediatric Surgery, Kaunas University of Medicine, Lithuania
2 Department of Radiology, Kaunas University of Medicine, Lithuania
Objective. To assess what degree of chest wall deformation changes statistically reliably after surgery, using pre- and postoperative radiological examination data. Methods. Radiological chest examinations were performed for 88 children before and after remedial operations. Pre- and postoperative chest radiograph and CT were performed to measure transversal chest width; sagittal left chest side depth, sagittal right chest side depth, sternovertebral distance, and vertebral body length. Derivative indices were also estimated: Vertebral index (VI), Frontosagittal index (FI), Haller index (HI) and asymmetry index. Computerized assessment of data was used. For statistical analysis, the software "Statistica 6.0" was used. Results. Postoperatively VI increased approximately by 2.37±2.72, FI decreased by 4.60±4.34, and HI value increased approximately up by 0.45±0.49. Statistically significant deformation index difference before and after surgery was not detected when VI was below 26.2 (p=0.08), FI was above 32.9 (p=0.079) and HI was less than 3.12 (p=0.098). Conclusion. Preoperative CT and X-ray assessment of chest wall deformation degree is important for pediatric patients. The following deformation indices are indications for surgical treatment: VI>26, FSI<33 and HI>3.1.
Keywords: Funnel chest; Pectus excavatum; Preoperative radiological assessment; Chest wall deformation indices; Children
Funnel chest (pectus excavatum) is among the most prevalent congenital chest wall deformities, with incidence of 1/300 children, which causes various disturbances.[1],[2],[3],[4],[5] Funnel chest compresses chest organs and causes cardio-respiratory disorders (heart palpitations, tachycardia, disturbed comprehensive inspiration, etc.). These problems lead to impaired child development and physical exercise limitation.[2],[4],[6] Recently, more evidence has appeared that only severe chest wall deformation can cause malfunctioning of chest organs.[4],[7],[8] It is claimed that depressed chest wall influences child's psychological state, which, in turn, inflict psychosomatic disturbances and physical exercise limitations.[8],[9] Cosmetic and psychological indications for surgical treatment gained more importance after minimally invasive and providing better cosmetic results Nuss operation for pectus excavatum had been introduced.[10],[11],[12] For assessment of indications for surgically corrective treatment, radiological examination is of great significance. Even in cases of moderate chest wall deformation with no signs of chest organ compression, indications for surgery can be determined by size of deformation seen on chest radiograph or CT.[13] Therefore, surgical treatment can solve cosmetic and/or psychological problems, as well as remedy smaller scale deformations.[8],[9],[10]
Precise radiological assessment parameters delineating the limits of norm and pathology have not yet been defined. Authors aim to report the experience of our departments regarding treatment of pediatric patients with pectus excavatum and to suggest an algorithm for radiological examination along with radiological indications for surgery.
Materials and Methods
88 children with pectus excavatum were examined and operated during 2000-2004 in the Department of Pediatric Surgery of our Medical University Hospital. For all patients radiograph was performed before and one month after the operation.
Informed consent has been obtained from patients/their representatives, as well as all the followed procedures were carried out in accordance with the ethical standards of the responsible committee of Kaunas University of Medicine and with the Helsinki Declaration of 1975, revised in 2000.
Before surgery, all of the 88 children underwent frontal and left lateral chest X-ray examination in the vertical position. A regular viewing-box and a ferule, calibrated to 1 mm accuracy, were used to evaluate radiographs.
CT scanning was performed for 58 children appointed to the investigation by a reffering physician. Investigation was performed by Siemens Somatom Plus 4 ( Siemens AG ) spiral CT scanner. During the examination, the patient was in the typical chest scanning position, breathing withheld. To avoid excessive exposure to X-rays, a single CT slice was performed in the most concave chest part on inhalation and exhalation. The distances were measured to the accuracy of 1 mm. The following values were measured: transverse distance of the chest wall, sagittal length of the chest left and right side, sternovertebral distance and vertebral body length [Figure - 1]. Arithmetic mean of values measured on inspiration and expiration was calculated in order to reduce error probability. Deformation indices were calculated according to K.Ohno's method.[8]
VI, FSI and HI were evaluated on X-ray and CT images. The obtained data had strong correlation (correlation coefficient r=0.96, p<0.0001). As supplementary dimensions, chest flatness and chest asymmetry index were assessed on CT scans. Chest flatness index = 2a/b+b 1 . If chest flatness index is below 2, chest is considered flat. If this value is 2 or higher, chest is regarded as normal. In assessment of chest asymmetry, left and right side chest depth ratio was calculated, according to the following equation: Asymmetry index = 1 - (b/b 1 ), where b/b 1 is left and right side chest depth ratio on inspiration and expiration.
Chest wall is considered "asymmetric" if asymmetry index is <- 0.05 (left side of the chest is more convex) or >0.05 (right side of the chest is more convex). Critical range [0.05] is set in accordance with the 5% error probability.
If VI 3 30, FSI ￡ 30 and HI 3 3.3, deformation indices are considered as "high". If VI<30, FSI>30 and HI<3.3, deformation indices are "low".[13] If at least one of the indices (VI, FSI or HI) is identified as "high", a pediatric patient is ascribed to a group of roentgenologically "severe" deformation. If the indices are "low", deformation roentgenologically is regarded as "moderate". "Severe" deformation was diagnosed in 34 (38.6%), "moderate" - in 54 children (61.4%).
Statistical analysis was performed by "STATISTICA 6.0" software. Parametric data were compared according to the t-Student method. Mean values were compared by the method of two independent samples. Postoperative results were assessed by analyzing the same data according to the pair (dependent) sample method. If sample contained less than 30 values or if these values did not match normal distribution law, mean values were compared using methods of non-parametrical statistics (Mann-Whitney-U method for parametric values and Wilcoxson method for the range values).
Results
67 children were operated by Ravitch method, attaching the sternum by external tractive suture. 21 children were operated by the minimally invasive Nuss method. Statistically significant differences with regard to age, sex, or degree of the deformation were not detected in both groups. Postoperatively, deformation indices exhibited the same changes in both groups. The sternovertebral distance increased to 1.49±1.23 cm in the group where Nuss method was applied, whereas the distance increased to 1.02±0.98 (p=0.258) in the group where Ravitch method was applied, indicating that the change in the sternovertebral distance is independent of the operation method. Comparison of index changes before and after the surgery is presented in [Table - 1].
Postoperatively VI decreased by 2.73±2.72 on average (range from 0 to 12.32), FSI increased by 4.60±4.34 on average (range from 0 to 20.00). The mean value of increase of HI was 0.45±0.49 (maximum increase was 2.33).
Increase of sternovertebral distance was directly dependent on roentgenologically "severe" and "moderate" deformation difference. In case of "moderate" deformation, sternovertebral distance increased to 11.23±10.91% whereas, in case of "severe" deformation, the distance increased to 28.3±26.82%, p=0.014 [Figure - 2]. Statistically significant differences between deformation indices pre- and post surgery were missing when VI <26.2 (p=0.08), FSI >32.9 (p=0.079) and HI < 3.12 (p=0.098) were detected preoperatively.
Discussion
Since changes of chest wall bones constitute the main anatomic component of chest wall deformities, radiological chest examination enables assessment of chest condition, deformation degree and shape. It also allows planning the operation, predicting its results and treatment outcome.[1],[3],[8],[13],[14],[15] Frontal and lateral chest radiograph helps to reveal the severity of deformation. For a comprehensive chest wall assessment, however, chest CT scanning is essential. The latter enables us to visualize not only chest shape but also presents exact topography of chest organs.[13],[16],[17] Authors believe that radiological examination gives precise objective assessment of and postoperative results and adds substantially to subjective criteria, the opinion of a child or family. It has been reported that the majority of patients give a positive evaluation of corrective surgery right after the operation. After some time, however, they become dissatisfied with its cosmetic or functional results.[8],[13] In addition, after a prolonged period of time, more people become disappointed with surgical results.[8] Radiological examination data enable us to determine exact indications for surgery, to select a relevant surgical technique and to envisage changes in the sternum location, as well as in the shape of chest.
Basing on our results suggest that, preoperative frontal and lateral chest radiograph and CT scanning should be performed for all children. If deformation is visually "severe" and surgery is inevitable, CT scanning can substitute chest radiograph. CT allows a more accurate assessment of relevant deformation indices, evaluation of chest shape and asymmetry. If full CT scanning is performed, a child is exposed to large doses of radiation. Therefore, after scout scanning, it is recommended to perform only single-slice scanning in the most concave level of the chest. CT scanning on inspiration and expiration is recommended in order to diminish error caused by chest wall excursion during breathing. Such CT scans do not provide lung pattern, nor Mediastinum configuration. For this reason, authors perform single-slice CT for children with no respiratory and cardiovascular disturbances or for children who underwent X-ray examination for other reasons that same year. Although chest radiograph enables assessment of main deformation indices, it is not sufficient to evaluate chest flatness and asymmetry. These values are essential for surgery planning and choosing the type of sternum stabilization.[2],[4],[6],[8],[13],[14],[16],[17]
The increase of sternovertebral distance was directly dependent on preoperatively assessed deformation index: the more severe deformation before operation, the bigger is the change. It was authors objective to find when the deformation index postoperatively remains reliably stable, i.e. what the deformation index limit is when the operation does not increase sternovertebral distance. The analysis revealed that sternovertebral distance increases below 5% if preoperatively VI mean value was <26.2, FSI>32.9, and HI<3.12. The findings are very close to those reported in the literature on the subject, specifically, in the description of cases when chest is considered to be of regular configuration, if VI<28. FSI>28 and HI<3.2.[2],[6],[8],[13],[14],[16]
Chest deformation indices are closely interrelated. VI characterizes skeletal and funnel depth ratio. FSI reveals chest width, but does not depend on the vertebra size. FSI demonstrates statistically significant correlation with child's age. Consequently, it may be misleading to rely only on this index for the assessment of relation between sternum and spine. FSI also depends on child's age: higher VI was found in younger children.[8], [18] For the evaluation of deformation, it is important to consider not only separate deformation indices but also the totality of those indices. Precise evaluation is possible only by computed analysis whereas manual calculation of all deformation indices and their assessment is inaccurate and time consuming.
It is recommended to classify roentgenologically tested deformation as "severe" or "moderate". If a single deformation index exceeds critical value (VI>28, FSI<33, HI >3.2), deformation is regarded as "severe". If all indices are below critical value, it is "moderate." Other authors present similar deformation index limits.[2],[4],[5],[7],[8],[13],[14],[16] Such method of assessment allows establishing precise indications for surgery since, in cases of "severe" deformation; there is a statistically reliable increase of sternovertebral distance, as well as other deformation indices. Such a classification is important for practical purposes, too. Authors results demonstrated that the ranges of critical deformation index values corresponded to statistically reliable increase of chest volume. In cases of "moderate" chest wall deformation, the sternum position does not change significantly with respect to spine. However, if VI<26, FSI>33 and HI is <3.1, it is very likely that sternum position will remain unchanged with respect to spine, especially in cases of flat chest. In such cases it is important to evaluate the child's posture initially: if it is incorrect, chest often visually looks deformed.[15],[19],[20] This is different in cases with asymmetric chest, when it should be immediately corrected to avoid the development of scoliosis.[20]
The study has certain limitations. One of them is that due to insufficient number of investigations we could not evaluate statistical significance of postoperative shape of chest. Chest flatness and chest asymmetry were not assessed in postoperative period because only a few children passed postoperative CT evaluation yet. Also correlation between the imaging data with the clinical data is beyond the scope of this article. Authors did not present evaluation of imaging indices for pectus excavatum with other possible outcomes of repair of pectus excavatum, such as post operative short and long term patient's satisfaction, clinical evaluation of the residual chest wall deformity and lung function test in severe cases of pectus excavatum.
In the present study we tried to establish the first step to an overall preoperative chest wall evaluation system, basing not on separate indices but on interaction of various postoperative indices. Using this evaluation it could be possible to determine whether the alteration of bony cage of chest wall will be statistically significant after operation.
Conclusion
When preparing a pediatric patient for a surgical pectus excavatum correction, it is important to perform CT scanning and give an overall evaluation of the chest shape and deformation degree. The following deformation indices are considered indications for surgically corrective treatment: VI>26, FSI<33 and HI>3.1.
References
1.Donnelly LF, Frush DP. Abnormalities of the chest wall in pediatric patients. AJR Am J Roentgenol 1999 December; 173(6): 1595-1601.
2.Fonkalsrud EW, Dunn JC, Atkinson JB. Repair of pectus excavatum deformities: 30 years of experience with 375 patients. Ann Surg 2000 March; 231(3) : 443-448.
3.Golladay ES, Golladay GJ. Chest wall deformities. Indian J Pediatr 1997 May; 64(3) : 339-350.
4.Saxena AK, Schaarschmidt K, Schleef J, Morcate JJ, Willital GH. Surgical correction of pectus excavatum: the Munster experience. Langenbecks Arch Surg 1999 April; 384(2) : 187-193.
5.Suita S, Taguchi T, Masumoto K, Kubota M, Kamimura T. Funnel chest: treatment strategy and follow-up. Pediatr Surg Int 2001 July;17(5-6) : 344-350.
6.Haller JA, Jr., Scherer LR, Turner CS, Colombani PM. Evolving management of pectus excavatum based on a single institutional experience of 664 patients. Ann Surg 1989 May; 209(5) : 578-582.
7.Kaguraoka H, Ohnuki T, Itaoka T, Kei J, Yokoyama M, Nitta S. Degree of severity of pectus excavatum and pulmonary function in preoperative and postoperative periods. J Thorac Cardiovasc Surg 1992 November; 104(5) : 1483-1488.
8.Ohno K, Nakahira M, Takeuchi S, Shiokawa C, Moriuchi T, Harumoto K, Nakaoka T, Ueda M, Yoshida T, Tsujimoto K, Kinoshita H. Indications for surgical treatment of funnel chest by chest radiograph. Pediatr Surg Int 2001 November; 17(8) : 591-595.
9.Einsiedel E, Clausner A. Funnel chest. Psychological and psychosomatic aspects in children, youngsters, and young adults. J Cardiovasc Surg (Torino) 1999 October;40(5) : 733-673.
10.Croitoru DP, Kelly RE, Jr., Goretsky MJ, Lawson ML, Swoveland B, Nuss D. Experience and modification update for the minimally invasive Nuss technique for pectus excavatum repair in 303 patients. J Pediatr Surg 2002 March; 37(3) : 437-445.
11.Hosie S, Sitkiewicz T, Petersen C, Gobel P, Schaarschmidt K, Till H, Noatnick M, Winiker H, Hagl C, Schmedding A, Waag KL. Minimally invasive repair of pectus excavatum-the Nuss procedure. A European multicentre experience. Eur J Pediatr Surg 2002 August; 12(4) : 235-238.
12.Miller KA, Woods RK, Sharp RJ, Gittes GK, Wade K, Ashcraft KW, Snyder CL, Andrews WM, Murphy JP, Holcomb GW, III. Minimally invasive repair of pectus excavatum: a single institution's experience. Surgery 2001 October;130(4) : 652-657.
13.Ohno K, Morotomi Y, Nakahira M, Takeuchi S, Shiokawa C, Moriuchi T, Harumoto K, Nakaoka T, Ueda M, Yoshida T, Yamada H, Tsujimoto K, Kinoshita H. Indications for surgical repair of funnel chest based on indices of chest wall deformity and psychological state. Surg Today 2003; 33(9) : 662-665.
14.de Matos AC, Bernardo JE, Fernandes LE, Antunes MJ. Surgery of chest wall deformities. Eur J Cardiothorac Surg 1997 September; 12(3) : 345-350.
15.Donnelly LF, Frush DP, Foss JN, O'Hara SM, Bisset GS, III. Anterior chest wall: frequency of anatomic variations in children. Radiology 1999 September; 212(3) : 837-840.
16.Nakahara K, Ohno K, Miyoshi S, Maeda H, Monden Y, Kawashima Y. An evaluation of operative outcome in patients with funnel chest diagnosed by means of the computed tomogram. J Thorac Cardiovasc Surg 1987 April; 93(4) : 577-582.
17.Willital GH. [Indication and operative technique in chest deformities (author's transl)]. Z Kinderchir 1981 July;33(3) : 244-252.
18.Ohno K, Morotomi Y, Ueda M, Yamada H, Shiokawa C, Nakaoka T, Tsujimoto K, Nakahira M, Moriuchi T, Harumoto K, Yoshida T. Comparison of the Nuss procedure for pectus excavatum by age and uncommon complications. Osaka City Med J 2003 December; 49(2) : 71-76.
19.Frick SL. Scoliosis in children with anterior chest wall deformities. Chest Surg Clin N Am 2000 May; 10(2) : 427-436.
20.Waters P, Welch K, Micheli LJ, Shamberger R, Hall JE. Scoliosis in children with pectus excavatum and pectus carinatum. J Pediatr Orthop 1989 September; 9(5) : 551-556.(Kilda Arturas, Basevicius Algidas, Barau)
2 Department of Radiology, Kaunas University of Medicine, Lithuania
Objective. To assess what degree of chest wall deformation changes statistically reliably after surgery, using pre- and postoperative radiological examination data. Methods. Radiological chest examinations were performed for 88 children before and after remedial operations. Pre- and postoperative chest radiograph and CT were performed to measure transversal chest width; sagittal left chest side depth, sagittal right chest side depth, sternovertebral distance, and vertebral body length. Derivative indices were also estimated: Vertebral index (VI), Frontosagittal index (FI), Haller index (HI) and asymmetry index. Computerized assessment of data was used. For statistical analysis, the software "Statistica 6.0" was used. Results. Postoperatively VI increased approximately by 2.37±2.72, FI decreased by 4.60±4.34, and HI value increased approximately up by 0.45±0.49. Statistically significant deformation index difference before and after surgery was not detected when VI was below 26.2 (p=0.08), FI was above 32.9 (p=0.079) and HI was less than 3.12 (p=0.098). Conclusion. Preoperative CT and X-ray assessment of chest wall deformation degree is important for pediatric patients. The following deformation indices are indications for surgical treatment: VI>26, FSI<33 and HI>3.1.
Keywords: Funnel chest; Pectus excavatum; Preoperative radiological assessment; Chest wall deformation indices; Children
Funnel chest (pectus excavatum) is among the most prevalent congenital chest wall deformities, with incidence of 1/300 children, which causes various disturbances.[1],[2],[3],[4],[5] Funnel chest compresses chest organs and causes cardio-respiratory disorders (heart palpitations, tachycardia, disturbed comprehensive inspiration, etc.). These problems lead to impaired child development and physical exercise limitation.[2],[4],[6] Recently, more evidence has appeared that only severe chest wall deformation can cause malfunctioning of chest organs.[4],[7],[8] It is claimed that depressed chest wall influences child's psychological state, which, in turn, inflict psychosomatic disturbances and physical exercise limitations.[8],[9] Cosmetic and psychological indications for surgical treatment gained more importance after minimally invasive and providing better cosmetic results Nuss operation for pectus excavatum had been introduced.[10],[11],[12] For assessment of indications for surgically corrective treatment, radiological examination is of great significance. Even in cases of moderate chest wall deformation with no signs of chest organ compression, indications for surgery can be determined by size of deformation seen on chest radiograph or CT.[13] Therefore, surgical treatment can solve cosmetic and/or psychological problems, as well as remedy smaller scale deformations.[8],[9],[10]
Precise radiological assessment parameters delineating the limits of norm and pathology have not yet been defined. Authors aim to report the experience of our departments regarding treatment of pediatric patients with pectus excavatum and to suggest an algorithm for radiological examination along with radiological indications for surgery.
Materials and Methods
88 children with pectus excavatum were examined and operated during 2000-2004 in the Department of Pediatric Surgery of our Medical University Hospital. For all patients radiograph was performed before and one month after the operation.
Informed consent has been obtained from patients/their representatives, as well as all the followed procedures were carried out in accordance with the ethical standards of the responsible committee of Kaunas University of Medicine and with the Helsinki Declaration of 1975, revised in 2000.
Before surgery, all of the 88 children underwent frontal and left lateral chest X-ray examination in the vertical position. A regular viewing-box and a ferule, calibrated to 1 mm accuracy, were used to evaluate radiographs.
CT scanning was performed for 58 children appointed to the investigation by a reffering physician. Investigation was performed by Siemens Somatom Plus 4 ( Siemens AG ) spiral CT scanner. During the examination, the patient was in the typical chest scanning position, breathing withheld. To avoid excessive exposure to X-rays, a single CT slice was performed in the most concave chest part on inhalation and exhalation. The distances were measured to the accuracy of 1 mm. The following values were measured: transverse distance of the chest wall, sagittal length of the chest left and right side, sternovertebral distance and vertebral body length [Figure - 1]. Arithmetic mean of values measured on inspiration and expiration was calculated in order to reduce error probability. Deformation indices were calculated according to K.Ohno's method.[8]
VI, FSI and HI were evaluated on X-ray and CT images. The obtained data had strong correlation (correlation coefficient r=0.96, p<0.0001). As supplementary dimensions, chest flatness and chest asymmetry index were assessed on CT scans. Chest flatness index = 2a/b+b 1 . If chest flatness index is below 2, chest is considered flat. If this value is 2 or higher, chest is regarded as normal. In assessment of chest asymmetry, left and right side chest depth ratio was calculated, according to the following equation: Asymmetry index = 1 - (b/b 1 ), where b/b 1 is left and right side chest depth ratio on inspiration and expiration.
Chest wall is considered "asymmetric" if asymmetry index is <- 0.05 (left side of the chest is more convex) or >0.05 (right side of the chest is more convex). Critical range [0.05] is set in accordance with the 5% error probability.
If VI 3 30, FSI ￡ 30 and HI 3 3.3, deformation indices are considered as "high". If VI<30, FSI>30 and HI<3.3, deformation indices are "low".[13] If at least one of the indices (VI, FSI or HI) is identified as "high", a pediatric patient is ascribed to a group of roentgenologically "severe" deformation. If the indices are "low", deformation roentgenologically is regarded as "moderate". "Severe" deformation was diagnosed in 34 (38.6%), "moderate" - in 54 children (61.4%).
Statistical analysis was performed by "STATISTICA 6.0" software. Parametric data were compared according to the t-Student method. Mean values were compared by the method of two independent samples. Postoperative results were assessed by analyzing the same data according to the pair (dependent) sample method. If sample contained less than 30 values or if these values did not match normal distribution law, mean values were compared using methods of non-parametrical statistics (Mann-Whitney-U method for parametric values and Wilcoxson method for the range values).
Results
67 children were operated by Ravitch method, attaching the sternum by external tractive suture. 21 children were operated by the minimally invasive Nuss method. Statistically significant differences with regard to age, sex, or degree of the deformation were not detected in both groups. Postoperatively, deformation indices exhibited the same changes in both groups. The sternovertebral distance increased to 1.49±1.23 cm in the group where Nuss method was applied, whereas the distance increased to 1.02±0.98 (p=0.258) in the group where Ravitch method was applied, indicating that the change in the sternovertebral distance is independent of the operation method. Comparison of index changes before and after the surgery is presented in [Table - 1].
Postoperatively VI decreased by 2.73±2.72 on average (range from 0 to 12.32), FSI increased by 4.60±4.34 on average (range from 0 to 20.00). The mean value of increase of HI was 0.45±0.49 (maximum increase was 2.33).
Increase of sternovertebral distance was directly dependent on roentgenologically "severe" and "moderate" deformation difference. In case of "moderate" deformation, sternovertebral distance increased to 11.23±10.91% whereas, in case of "severe" deformation, the distance increased to 28.3±26.82%, p=0.014 [Figure - 2]. Statistically significant differences between deformation indices pre- and post surgery were missing when VI <26.2 (p=0.08), FSI >32.9 (p=0.079) and HI < 3.12 (p=0.098) were detected preoperatively.
Discussion
Since changes of chest wall bones constitute the main anatomic component of chest wall deformities, radiological chest examination enables assessment of chest condition, deformation degree and shape. It also allows planning the operation, predicting its results and treatment outcome.[1],[3],[8],[13],[14],[15] Frontal and lateral chest radiograph helps to reveal the severity of deformation. For a comprehensive chest wall assessment, however, chest CT scanning is essential. The latter enables us to visualize not only chest shape but also presents exact topography of chest organs.[13],[16],[17] Authors believe that radiological examination gives precise objective assessment of and postoperative results and adds substantially to subjective criteria, the opinion of a child or family. It has been reported that the majority of patients give a positive evaluation of corrective surgery right after the operation. After some time, however, they become dissatisfied with its cosmetic or functional results.[8],[13] In addition, after a prolonged period of time, more people become disappointed with surgical results.[8] Radiological examination data enable us to determine exact indications for surgery, to select a relevant surgical technique and to envisage changes in the sternum location, as well as in the shape of chest.
Basing on our results suggest that, preoperative frontal and lateral chest radiograph and CT scanning should be performed for all children. If deformation is visually "severe" and surgery is inevitable, CT scanning can substitute chest radiograph. CT allows a more accurate assessment of relevant deformation indices, evaluation of chest shape and asymmetry. If full CT scanning is performed, a child is exposed to large doses of radiation. Therefore, after scout scanning, it is recommended to perform only single-slice scanning in the most concave level of the chest. CT scanning on inspiration and expiration is recommended in order to diminish error caused by chest wall excursion during breathing. Such CT scans do not provide lung pattern, nor Mediastinum configuration. For this reason, authors perform single-slice CT for children with no respiratory and cardiovascular disturbances or for children who underwent X-ray examination for other reasons that same year. Although chest radiograph enables assessment of main deformation indices, it is not sufficient to evaluate chest flatness and asymmetry. These values are essential for surgery planning and choosing the type of sternum stabilization.[2],[4],[6],[8],[13],[14],[16],[17]
The increase of sternovertebral distance was directly dependent on preoperatively assessed deformation index: the more severe deformation before operation, the bigger is the change. It was authors objective to find when the deformation index postoperatively remains reliably stable, i.e. what the deformation index limit is when the operation does not increase sternovertebral distance. The analysis revealed that sternovertebral distance increases below 5% if preoperatively VI mean value was <26.2, FSI>32.9, and HI<3.12. The findings are very close to those reported in the literature on the subject, specifically, in the description of cases when chest is considered to be of regular configuration, if VI<28. FSI>28 and HI<3.2.[2],[6],[8],[13],[14],[16]
Chest deformation indices are closely interrelated. VI characterizes skeletal and funnel depth ratio. FSI reveals chest width, but does not depend on the vertebra size. FSI demonstrates statistically significant correlation with child's age. Consequently, it may be misleading to rely only on this index for the assessment of relation between sternum and spine. FSI also depends on child's age: higher VI was found in younger children.[8], [18] For the evaluation of deformation, it is important to consider not only separate deformation indices but also the totality of those indices. Precise evaluation is possible only by computed analysis whereas manual calculation of all deformation indices and their assessment is inaccurate and time consuming.
It is recommended to classify roentgenologically tested deformation as "severe" or "moderate". If a single deformation index exceeds critical value (VI>28, FSI<33, HI >3.2), deformation is regarded as "severe". If all indices are below critical value, it is "moderate." Other authors present similar deformation index limits.[2],[4],[5],[7],[8],[13],[14],[16] Such method of assessment allows establishing precise indications for surgery since, in cases of "severe" deformation; there is a statistically reliable increase of sternovertebral distance, as well as other deformation indices. Such a classification is important for practical purposes, too. Authors results demonstrated that the ranges of critical deformation index values corresponded to statistically reliable increase of chest volume. In cases of "moderate" chest wall deformation, the sternum position does not change significantly with respect to spine. However, if VI<26, FSI>33 and HI is <3.1, it is very likely that sternum position will remain unchanged with respect to spine, especially in cases of flat chest. In such cases it is important to evaluate the child's posture initially: if it is incorrect, chest often visually looks deformed.[15],[19],[20] This is different in cases with asymmetric chest, when it should be immediately corrected to avoid the development of scoliosis.[20]
The study has certain limitations. One of them is that due to insufficient number of investigations we could not evaluate statistical significance of postoperative shape of chest. Chest flatness and chest asymmetry were not assessed in postoperative period because only a few children passed postoperative CT evaluation yet. Also correlation between the imaging data with the clinical data is beyond the scope of this article. Authors did not present evaluation of imaging indices for pectus excavatum with other possible outcomes of repair of pectus excavatum, such as post operative short and long term patient's satisfaction, clinical evaluation of the residual chest wall deformity and lung function test in severe cases of pectus excavatum.
In the present study we tried to establish the first step to an overall preoperative chest wall evaluation system, basing not on separate indices but on interaction of various postoperative indices. Using this evaluation it could be possible to determine whether the alteration of bony cage of chest wall will be statistically significant after operation.
Conclusion
When preparing a pediatric patient for a surgical pectus excavatum correction, it is important to perform CT scanning and give an overall evaluation of the chest shape and deformation degree. The following deformation indices are considered indications for surgically corrective treatment: VI>26, FSI<33 and HI>3.1.
References
1.Donnelly LF, Frush DP. Abnormalities of the chest wall in pediatric patients. AJR Am J Roentgenol 1999 December; 173(6): 1595-1601.
2.Fonkalsrud EW, Dunn JC, Atkinson JB. Repair of pectus excavatum deformities: 30 years of experience with 375 patients. Ann Surg 2000 March; 231(3) : 443-448.
3.Golladay ES, Golladay GJ. Chest wall deformities. Indian J Pediatr 1997 May; 64(3) : 339-350.
4.Saxena AK, Schaarschmidt K, Schleef J, Morcate JJ, Willital GH. Surgical correction of pectus excavatum: the Munster experience. Langenbecks Arch Surg 1999 April; 384(2) : 187-193.
5.Suita S, Taguchi T, Masumoto K, Kubota M, Kamimura T. Funnel chest: treatment strategy and follow-up. Pediatr Surg Int 2001 July;17(5-6) : 344-350.
6.Haller JA, Jr., Scherer LR, Turner CS, Colombani PM. Evolving management of pectus excavatum based on a single institutional experience of 664 patients. Ann Surg 1989 May; 209(5) : 578-582.
7.Kaguraoka H, Ohnuki T, Itaoka T, Kei J, Yokoyama M, Nitta S. Degree of severity of pectus excavatum and pulmonary function in preoperative and postoperative periods. J Thorac Cardiovasc Surg 1992 November; 104(5) : 1483-1488.
8.Ohno K, Nakahira M, Takeuchi S, Shiokawa C, Moriuchi T, Harumoto K, Nakaoka T, Ueda M, Yoshida T, Tsujimoto K, Kinoshita H. Indications for surgical treatment of funnel chest by chest radiograph. Pediatr Surg Int 2001 November; 17(8) : 591-595.
9.Einsiedel E, Clausner A. Funnel chest. Psychological and psychosomatic aspects in children, youngsters, and young adults. J Cardiovasc Surg (Torino) 1999 October;40(5) : 733-673.
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