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Meta-analysis of the risk of metachronous hernia in infants and children: An updated analysis
The American Journal of Surgery 189 (2005) 126 –128
Letters to the Editor Meta-analysis of the risk of metachronous hernia in infants and children: an updated analysis To the Editor: I read with interest the article by Miltenburg et al [1] reporting the results of a meta-analysis of metachronous hernia in infants and children. The authors used a metaanalysis to summarize the results of studies examining the rate of contralateral hernia on the originally asymptomatic side after a unilateral herniorrhaphy. Subsequent to the publication of this article, guidelines for conducting a metaanalysis have been given by Normand [2]. Applying these guidelines to the data given in Miltenburg et al give different results to those presented. Importantly, I find a significant heterogeneity between studies, whereas the authors found “no significant heterogeneity.” That is, there is significant variation in the incidence of metachronous hernia between the 35 studies cited (chi-square statistic ⫽ 304.3, degrees of freedom ⫽ 34, P ⬍ 0.001). This conclusion is based on the data given in Table 1 in the Miltenburg et al article [1]. The large variation between studies is clear in Figure 1, which plots the observed mean estimates and 95% confidence intervals for the incidence of metachronous hernia. The estimated range of mean incidence varies from 1% in the article by Tepas and Stafford [3] to 31% in the article by Kiesewetter and
Fig. 1. Random effects meta-analysis and study-specific 95% confidence intervals of the incidence of metachronous hernia in infants and children (35 studies). The horizontal lines extend to the 95% confidence interval, and the vertical line indicates the mean. There is a significant heterogeneity between studies. This is particularly noticeable for the results of Kiesewetter and Parenzan [4] compared with Tepas and Stafford [3].
Parenzan [4]. This heterogeneity between studies may be caused by differences in the studies procedures (eg, exclusion criteria), the population studied (eg, differences between countries or regions), and to some extent random variation. The test of heterogeneity tells us that the differences between studies is too large to be explained by random variation alone. Searching for differences between the studies that might explain the extra variation, we found that the article by Kiesewetter and Parenzan [4] followed-up patients for a maximum of 9 years, whereas Tepas and Stafford [3] followed patients for a maximum of 5 years. Perhaps more importantly, the subjects in the Kiesewetter and Parenzan study were aged 0 to 24 months, whereas those in the Tepas and Stafford study were aged 6 to 24 months. A greater risk of contralateral hernia in the 0- to 6-month age group was observed in both studies. Such information on the differences between studies should be collected and reported as part of the meta-analysis. These differences in study design may explain differences between the observed rates and be built into a statistical model (in much the same way that covariates are added to multiple-regression models). Because there is significant heterogeneity between the studies, a random effects meta-analysis is needed. This gives an estimated population incidence of meta-chronous hernia of 8.2% with a 95% posterior interval of 6.5% to 10.1%, compared with the results from Miltenburg et al (using a Mantel-Haenszel meta-analysis), which gave a population estimate of 7.0% and a narrower 95% confidence interval of 6.8% to 7.2%. The mean estimate from the random effects meta-analysis is slightly greater, and the 95% interval is much wider. This means that new studies in the area should not be surprised to see their mean rate of metachronous hernia fall within 6.5% and 10.1%. Note the random effects meta-analysis gives a 95% posterior interval, whereas the Mantel-Haenszel meta-analysis gives a 95% confidence interval. The Bayesian posterior interval has the simple interpretation that the true population incidence of metachronous hernia has a high probability of being contained within its limits. The 95% confidence interval does not have this simple interpretation (although a common mistake is to assume it does). Meta-analyses are a useful tool for summarizing similar studies from a number of sources. They also have more power than individual studies, and hence carry more weight in terms of evidence-based medicine. Therefore, it is important that they are analyzed carefully. The authors did a
0002-9610/05/$ – see front matter © 2005 Excerpta Medica Inc. All rights reserved.
Letters to the Editor / The American Journal of Surgery 189 (2005) 126 –128
good job of collating the information and presented an adequate statistical analysis. However, a key part of metaanalysis is to assess the differences between studies that might explain disparities in the results (eg, exclusion criteria, age of subjects, length of follow-up). I encourage readers who are planning a meta-analysis to follow the guidelines given in the article by Normand [2]. This includes the steps of citing the sources of the data (eg, unpublished report) and the methods used to search for relevant papers, plotting the observed data, assessing the heterogeneity between studies, assessing the impact of publication bias, and combining the data using a random-effects meta-analysis. Adrian G. Barnett, Ph.D. School of Population Health University of Queensland Herston, Australia
The “components separation technique” is a helpful technique for septic conditions and occasionally to obtain adequate relaxation to close the midline fascia during a RivesStoppa-Wantz repair. However, the suggestion that the separation of parts repair is generally indicated for large midline incisional hernias is again premature. The few studies of component separation had a modest number of patients with short follow-up. The long-term results are not known. The re-herniation rate was 32% in the most recent study reported [6]. This maybe be acceptable when mesh is contraindicated, but it is not the standard surgeons would accept in clean cases. At this time, I believe the gold standard for repair of midline incisional hernias is the Rives-Stoppa-Wantz repair. The laparoscopic and “components separation” techniques have a role, but it is yet to be defined. Brent W. Miedema, M.D. Department of Surgery University of Missouri Health Sciences Center Columbia, Missouri
doi:10.1016/j.amjsurg.2004.08.031
References [1] Miltenburg D, Nuchtern J, Jaksic T, et al. Meta-analysis of the risk of metachronous hernia in infants and children. Am J Surg 1997;174: 741–744. [2] Normand S. Meta-analysis: Formulating, evaluating, combining, and reporting, Stat Med 1999;18:321–359. [3] Tepas J, Stafford P. Timing of automatic contralateral groin exploration in male infants with unilateral hernias. Am Surg 1986;52:70 –71. [4] Kiesewetter W, Parenzan L. When should hernia in the infant be treated bilaterally? J Am Stat Assoc 1959;171:287–290.
To the Editor: I was pleased to see a review article in the January issue of The American Journal of Surgery on comparison of repair techniques for major incisional hernias [1]. It is the opinion of many herniologists that the Rives-Stoppa-Wantz repair is the repair of choice for most incisional hernias [2]. I was interested to see how the authors would view the use of new techniques compared to the old standard. I was quite surprised when the Rives- Stoppa-Wantz repair was not even mentioned in the article. In the author’s algorithm for patient management, the options are direct repair, laparoscopic repair, and separation of parts repair. Is there no indication for the Rives-Stoppa-Wantz repair in modern day hernia surgery? The authors make the assumption that laparoscopic repair of incisional hernia has a low recurrence rate. I believe this assumption is premature as the long-term data are not in yet. A recent French study reported a recurrence rate of 16% with longer (49 months) follow-up [3]. A study from the Cleveland clinic documented a 17% recurrence at an average of 30 months of follow-up [4]. Different individuals from this same institution claimed a low recurrence rate in a prior report [5].
127
doi:10.1016/j.amjsurg.2004.08.010
References [1] Dumanian GA, Deham W. Comparison of repair techniques for major incisional hernias. Am J Surg 2003;185:61–5. [2] Anonymous. Incisional hernia: The problem and the cure. J Am Coll Surg 1999;188:429 – 47. [3] Bageacu S, Blanc P, Breton C, et al. Laparoscopic repair of incisional hernia. A retrospective study of 159 patients. Surg Endosc 2002;16: 345– 8. [4] Rosen M, Brody F, Ponsky J, et al. Recurrence after laparoscopic ventral hernia repair. A five-year experience. Surg Endosc 2003;17: 123– 8. [5] Costanza MJ, Heniford BT, Arca MJ, Mayes JT, Gagner M. Laparscopic repair of recurrent ventral hernias. Am Surg 1998;64:1121–7. [6] de Vries Reilingh TS, van Goor H, Rosman C, et al. “Components separation technique” for the repair of large abdominal wall hernias. J Am Coll Surg 2003;196:32–7.
Predictors of nonsentinel lymph node metastases in breast cancer patients To the Editor: We read with interest the study by Sachdev et al in The Amercan Journal of Surgery [1]. The authors have raised some very valid issues. However, we have certain reservations regarding their results and observations. The authors do not mention any exclusion criteria for the 212 patients taken up for sentinel lymph node biopsy. Well-accepted criteria include the presence of palpable axillary nodes, previous axillary surgery, and diffuse disease [2]. This may in part be responsible for the relatively low rate of successful sentinel lymph node identification and biopsy in the present series. Another possible factor would be the sole use
Letters to the Editor Meta-analysis of the risk of metachronous hernia in infants and children: an updated analysis To the Editor: I read with interest the article by Miltenburg et al [1] reporting the results of a meta-analysis of metachronous hernia in infants and children. The authors used a metaanalysis to summarize the results of studies examining the rate of contralateral hernia on the originally asymptomatic side after a unilateral herniorrhaphy. Subsequent to the publication of this article, guidelines for conducting a metaanalysis have been given by Normand [2]. Applying these guidelines to the data given in Miltenburg et al give different results to those presented. Importantly, I find a significant heterogeneity between studies, whereas the authors found “no significant heterogeneity.” That is, there is significant variation in the incidence of metachronous hernia between the 35 studies cited (chi-square statistic ⫽ 304.3, degrees of freedom ⫽ 34, P ⬍ 0.001). This conclusion is based on the data given in Table 1 in the Miltenburg et al article [1]. The large variation between studies is clear in Figure 1, which plots the observed mean estimates and 95% confidence intervals for the incidence of metachronous hernia. The estimated range of mean incidence varies from 1% in the article by Tepas and Stafford [3] to 31% in the article by Kiesewetter and
Fig. 1. Random effects meta-analysis and study-specific 95% confidence intervals of the incidence of metachronous hernia in infants and children (35 studies). The horizontal lines extend to the 95% confidence interval, and the vertical line indicates the mean. There is a significant heterogeneity between studies. This is particularly noticeable for the results of Kiesewetter and Parenzan [4] compared with Tepas and Stafford [3].
Parenzan [4]. This heterogeneity between studies may be caused by differences in the studies procedures (eg, exclusion criteria), the population studied (eg, differences between countries or regions), and to some extent random variation. The test of heterogeneity tells us that the differences between studies is too large to be explained by random variation alone. Searching for differences between the studies that might explain the extra variation, we found that the article by Kiesewetter and Parenzan [4] followed-up patients for a maximum of 9 years, whereas Tepas and Stafford [3] followed patients for a maximum of 5 years. Perhaps more importantly, the subjects in the Kiesewetter and Parenzan study were aged 0 to 24 months, whereas those in the Tepas and Stafford study were aged 6 to 24 months. A greater risk of contralateral hernia in the 0- to 6-month age group was observed in both studies. Such information on the differences between studies should be collected and reported as part of the meta-analysis. These differences in study design may explain differences between the observed rates and be built into a statistical model (in much the same way that covariates are added to multiple-regression models). Because there is significant heterogeneity between the studies, a random effects meta-analysis is needed. This gives an estimated population incidence of meta-chronous hernia of 8.2% with a 95% posterior interval of 6.5% to 10.1%, compared with the results from Miltenburg et al (using a Mantel-Haenszel meta-analysis), which gave a population estimate of 7.0% and a narrower 95% confidence interval of 6.8% to 7.2%. The mean estimate from the random effects meta-analysis is slightly greater, and the 95% interval is much wider. This means that new studies in the area should not be surprised to see their mean rate of metachronous hernia fall within 6.5% and 10.1%. Note the random effects meta-analysis gives a 95% posterior interval, whereas the Mantel-Haenszel meta-analysis gives a 95% confidence interval. The Bayesian posterior interval has the simple interpretation that the true population incidence of metachronous hernia has a high probability of being contained within its limits. The 95% confidence interval does not have this simple interpretation (although a common mistake is to assume it does). Meta-analyses are a useful tool for summarizing similar studies from a number of sources. They also have more power than individual studies, and hence carry more weight in terms of evidence-based medicine. Therefore, it is important that they are analyzed carefully. The authors did a
0002-9610/05/$ – see front matter © 2005 Excerpta Medica Inc. All rights reserved.
Letters to the Editor / The American Journal of Surgery 189 (2005) 126 –128
good job of collating the information and presented an adequate statistical analysis. However, a key part of metaanalysis is to assess the differences between studies that might explain disparities in the results (eg, exclusion criteria, age of subjects, length of follow-up). I encourage readers who are planning a meta-analysis to follow the guidelines given in the article by Normand [2]. This includes the steps of citing the sources of the data (eg, unpublished report) and the methods used to search for relevant papers, plotting the observed data, assessing the heterogeneity between studies, assessing the impact of publication bias, and combining the data using a random-effects meta-analysis. Adrian G. Barnett, Ph.D. School of Population Health University of Queensland Herston, Australia
The “components separation technique” is a helpful technique for septic conditions and occasionally to obtain adequate relaxation to close the midline fascia during a RivesStoppa-Wantz repair. However, the suggestion that the separation of parts repair is generally indicated for large midline incisional hernias is again premature. The few studies of component separation had a modest number of patients with short follow-up. The long-term results are not known. The re-herniation rate was 32% in the most recent study reported [6]. This maybe be acceptable when mesh is contraindicated, but it is not the standard surgeons would accept in clean cases. At this time, I believe the gold standard for repair of midline incisional hernias is the Rives-Stoppa-Wantz repair. The laparoscopic and “components separation” techniques have a role, but it is yet to be defined. Brent W. Miedema, M.D. Department of Surgery University of Missouri Health Sciences Center Columbia, Missouri
doi:10.1016/j.amjsurg.2004.08.031
References [1] Miltenburg D, Nuchtern J, Jaksic T, et al. Meta-analysis of the risk of metachronous hernia in infants and children. Am J Surg 1997;174: 741–744. [2] Normand S. Meta-analysis: Formulating, evaluating, combining, and reporting, Stat Med 1999;18:321–359. [3] Tepas J, Stafford P. Timing of automatic contralateral groin exploration in male infants with unilateral hernias. Am Surg 1986;52:70 –71. [4] Kiesewetter W, Parenzan L. When should hernia in the infant be treated bilaterally? J Am Stat Assoc 1959;171:287–290.
To the Editor: I was pleased to see a review article in the January issue of The American Journal of Surgery on comparison of repair techniques for major incisional hernias [1]. It is the opinion of many herniologists that the Rives-Stoppa-Wantz repair is the repair of choice for most incisional hernias [2]. I was interested to see how the authors would view the use of new techniques compared to the old standard. I was quite surprised when the Rives- Stoppa-Wantz repair was not even mentioned in the article. In the author’s algorithm for patient management, the options are direct repair, laparoscopic repair, and separation of parts repair. Is there no indication for the Rives-Stoppa-Wantz repair in modern day hernia surgery? The authors make the assumption that laparoscopic repair of incisional hernia has a low recurrence rate. I believe this assumption is premature as the long-term data are not in yet. A recent French study reported a recurrence rate of 16% with longer (49 months) follow-up [3]. A study from the Cleveland clinic documented a 17% recurrence at an average of 30 months of follow-up [4]. Different individuals from this same institution claimed a low recurrence rate in a prior report [5].
127
doi:10.1016/j.amjsurg.2004.08.010
References [1] Dumanian GA, Deham W. Comparison of repair techniques for major incisional hernias. Am J Surg 2003;185:61–5. [2] Anonymous. Incisional hernia: The problem and the cure. J Am Coll Surg 1999;188:429 – 47. [3] Bageacu S, Blanc P, Breton C, et al. Laparoscopic repair of incisional hernia. A retrospective study of 159 patients. Surg Endosc 2002;16: 345– 8. [4] Rosen M, Brody F, Ponsky J, et al. Recurrence after laparoscopic ventral hernia repair. A five-year experience. Surg Endosc 2003;17: 123– 8. [5] Costanza MJ, Heniford BT, Arca MJ, Mayes JT, Gagner M. Laparscopic repair of recurrent ventral hernias. Am Surg 1998;64:1121–7. [6] de Vries Reilingh TS, van Goor H, Rosman C, et al. “Components separation technique” for the repair of large abdominal wall hernias. J Am Coll Surg 2003;196:32–7.
Predictors of nonsentinel lymph node metastases in breast cancer patients To the Editor: We read with interest the study by Sachdev et al in The Amercan Journal of Surgery [1]. The authors have raised some very valid issues. However, we have certain reservations regarding their results and observations. The authors do not mention any exclusion criteria for the 212 patients taken up for sentinel lymph node biopsy. Well-accepted criteria include the presence of palpable axillary nodes, previous axillary surgery, and diffuse disease [2]. This may in part be responsible for the relatively low rate of successful sentinel lymph node identification and biopsy in the present series. Another possible factor would be the sole use