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Pediatric Imaging |
1 From the Department of Diagnostic and Interventional Radiology (C.R.H., F.W., M.C.C., J.K., G.A.), Institute for Medical Biometry and Epidemiology (V.S.), and Department of Neuroradiology (O.W.), University Hospital Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. Received September 18, 2003; revision requested December 2; final revision received April 7, 2004; accepted May 26. Address correspondence to C.R.H. (e-mail: c.habermann@uke.uni-hamburg.de).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Local ethics committee approval and informed consent were obtained. MR images of the lumbar spine in 28 patients with clinically proved Marfan syndrome (group A; 17 male, 11 female; age range, 4–21 years; mean, 12.1 years), seven patients with suspicion of Marfan syndrome (group B; six male, one female; age range, 6–18 years; mean, 10.4 years), and 55 patients without Marfan syndrome (group C; 26 male, 29 female; age range, 4–20 years; mean, 10.7 years) were evaluated retrospectively for dural ectasia criteria (scalloping, dural sac ratio, nerve root sleeve diameter, sagittal dural sac width at S1 greater than that at L4) and according to classifications by Ahn et al and Fattori et al. For statistical comparison of results, one-way analysis of variance with Scheffe post hoc comparisons was used, with an overall two-tailed significance at 
= .05.
RESULTS: No significant differences in scalloping and nerve root sleeve diameter were shown between groups. A significant difference was measured for dural sac ratios at L5 and S1 (F test, P = .003 and P < .001 at L5 and S1, respectively; post hoc t test for groups A vs C, P = .004 and P < .001 at L5 and S1, respectively). Significant differences were also obtained between groups A and C for sagittal dural sac width at S1 greater than that at L4 according to the calculated mean difference (for both F test and post hoc t test, P < .001 and P = .003 at S1 and L4, respectively). The Ahn et al and Fattori et al classifications were of limited value.
CONCLUSION: The data suggest that only dural sac ratio at L5 and S1 and a sagittal dural sac width at S1 greater than that at L4 are statistically significant criteria for the assessment of dural ectasia in children, adolescents, and young adults.
© RSNA, 2004
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Dural ectasia has been indirectly identified on conventional radiographs showing a scalloping of vertebral bodies (11). Other authors have noted that dural ectasia can be diagnosed accurately with magnetic resonance (MR) imaging and computed tomography (CT) (5,12–16). These authors evaluated adult patients or included only a few adolescents (14), but none of them proved their criteria for dural ectasia to be accurate in children, adolescents, and young adults.
Thus, the purpose of our study was to evaluate retrospectively the known criteria of dural ectasia by using MR imaging in children, adolescents, and young adults with and those without Marfan syndrome.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The study was conducted in accordance with the recommendations of the local ethics committee that approved it. In all patients younger than 18 years, informed parental consent was obtained, whereas in all other cases, informed consent was obtained from the patients.
MR Imaging
All examinations were performed by using a 1.5-T MR imaging system (Vision or Symphony; Siemens, Erlangen, Germany) and consisted of sagittal and transverse T2-weighted (repetition time msec/echo time msec, 4200/112) and sagittal T1-weighted (640/14) sequences. The technical specifications included intersection gaps of 1.0 and 0.5 mm for sagittal and transverse sequences, respectively, a field of view of 240–480 x 480 mm, a section thickness of 4 mm, and a matrix of 192 x 256, with two signals acquired. In addition, sagittal and coronal T2-weighted (4500/989) single-section rapid acquisition with relaxation enhancement sequences were performed, with a field of view of 350 x 350 mm, a section thickness of 100 mm, and a matrix of 333 x 512, with one signal acquired.
Evaluation Criteria
All images were evaluated on a monochrome 1000-pixel picture archiving and communication system monitor (Simomed; Siemens) and were read in consensus by two radiologists (C.R.H. and F.W., each with 8 years of experience in MR imaging) who were blinded to whether the patient had Marfan syndrome. Measurements were obtained on the sagittal and transverse T2-weighted images.
Scalloping
Scalloping, which is presumably caused by the ballooning of the dural sac, has been defined as a central erosion of the vertebral body as seen in the sagittal plane and has been associated with dural ectasia in previous reports (15,17,18). Scalloping values were calculated by measuring the superior sagittal diameters, the inferior sagittal diameters, and the midsagittal diameters of L5 and S1 (15). The superior and inferior diameters were added and then divided by two, and the midsagittal diameter was subtracted from this value (Fig 1). For this purpose, sagittal plane bony measurements were obtained from each outer black cortical vertebral margin. Ahn et al (15) defined scalloping greater than 3.5 mm at the level of S1 as a minor criterion for dural ectasia.
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Dural Sac Ratio
The midsagittal diameters or vertebral body diameters and the sagittal dural sac diameters were obtained at the levels of L1 through S1 (Fig 2). The sagittal dural sac diameter was measured perpendicular to the long axis of the dural sac, as indicated in Figure 1. A dural sac ratio was calculated for each level from L1 through S1 by dividing the dural sac diameter by the vertebral body diameter. According to Oosterhof et al (16), cut-off values for levels L1 through S1 in adult patients were 0.64, 0.55, 0.47, 0.48, 0.48, and 0.57.
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Nerve Root Sleeve Diameter
The nerve root sleeve diameters were evaluated on transverse T1-weighted images. The maximum diameter of the nerve root sleeves was measured for each foramen at each level from L1 through S1, and the arithmetic mean for each level was calculated and used for analysis. According to Ahn et al (15), a diameter exceeding 6.5 mm at the level of L5 represents a minor criterion for the presence of dural ectasia.
Evaluation of Dural Ectasia: Criteria by Ahn et al
Ahn et al (15) described two major criteria for the presence of dural ectasia: width of the dural sac at a level below L5 greater than that above L4 and presence of an anterior sacral meningocele. Minor criteria were defined as scalloping greater than 3.5 mm at the level of S1 and nerve root sleeve diameter greater than 6.5 mm at the level of L5. They concluded that dural ectasia is present if one major or two minor criteria are present.
Evaluation of Dural Ectasia: Criteria by Fattori et al
According to Fattori et al (14), the degree of dural abnormalities can be classified as follows: grade 1, mild dural ectasia defined by bulging of the dural sac and lack of epidural fat at the level of the posterior wall of one vertebral body, by the presence of small radicular cysts, or by both features; grade 2, moderate dural ectasia defined by bulging of the dural sac and lack of epidural fat at the level of the posterior wall of two or more vertebral bodies and presence of large radicular cysts; and grade 3, severe dural ectasia defined by presence of an anterior sacral meningocele.
Statistical Analysis
For all patients, the body mass index (BMI) was computed. Correlations between the BMI and the scalloping and dural sac ratio were computed to investigate any dependency. Analysis regarding differences between male and female patients was not performed.
Data are presented as relative frequencies and percentages for count data and as means and standard deviations for metric measures. For comparison between groups, a one-way analysis of variance with Scheffé post hoc comparisons was used, with an overall two-tailed significance level at = .05. To examine the age- and BMI-dependency of several results, correlation coefficients and regression models were used.
All statistical computations were performed by using SPSS 11.5 (SPSS, Chicago, Ill), except for calculation of receiver operating characteristic curve and area under the curve, for which ROCKIT (Kurt Rossmann Laboratories for Radiologic Image Research, Chicago, Ill) was used.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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All six pairwise correlations between age, BMI, scalloping at L5, and scalloping at S1 were computed. All coefficients were mildly positive, with a range of 0.13–0.42. The highest correlation was observed between age and scalloping at S1. Adjusting for age in a linear regression model with scalloping as a dependent variable did not change the results.
An anterior sacral meningocele could not be diagnosed in any of the 90 patients included in this study.
Dural Sac Ratio
The calculated dural sac ratios at levels L1 through S1 for all three groups are listed in Table 2. Comparisons between the three groups indicate that only locations L5 and S1 are suitable to help discriminate between groups (F test, P = .003 and P < .001 at L5 and S1, respectively; post hoc t test for groups A vs C, P = .004 and P < .001 at L5 and S1, respectively).
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There was a mild to moderate negative correlation between dural sac ratios and age, as well as between dural sac ratios and BMI, which ranged from –0.09 to –0.39; for locations L5 and S1, the absolute values of the correlations with age and BMI were below 0.25, which indicated that there was no considerable dependency between the dural sac ratio and the patient age and/or BMI.
Dural Sac Diameter at S1 Greater than That at L4
In 32% of patients (nine of 28) in group A, there was a greater sagittal dural sac diameter at S1 than at L4, with a mean difference of 0.75 mm and a standard deviation of 4.1 mm among all 28 patients. In 14% of patients (one of seven) in group B, there was a greater diameter at S1 than at L4, with a mean difference of 1.71 mm and a standard deviation of 2.1 mm. In 2% of patients (one of 55) in group C, there was a greater diameter at S1 than at L4, while in 15% of patients (eight of 55) the diameter was the same at both levels, with a mean difference of 3.25 mm and a standard deviation of 2.1 mm. The calculated mean difference between patients with Marfan syndrome (group A) and those with no suspicion of Marfan syndrome (group C) proved to be significant (for both F test and post hoc t test, P < .001 and P = .003 at S1 and L4, respectively).
Nerve Root Sleeve Diameter
The results for nerve root sleeve diameter of L1 to S1 are shown in Table 3. The diameter of a nerve root sleeve did not exceed 6.5 mm in any of the patients in groups A and B, whereas a nerve root sleeve diameter of 7 mm was measured at the level of L5 in 4% of patients (two of 55) in group C (control group). There was no statistically significant difference for any level between the three groups (P > .65 for all F tests).
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Evaluation of Dural Ectasia: Criteria by Ahn et al
In our study population, in the group with clinically proved Marfan syndrome (group A), the major criterion of dural sac diameter at S1 greater than that at L4 (Ahn et al [15]) was found for 32% of patients (nine of 28); in the control group, this criterion could only be determined in one patient (2%). One patient in group B (14%) also met this criterion. None of our 90 patients proved to have an anterior sacral meningocele as a second major criterion.
Within groups A and B, none of the patients proved to have a nerve root sleeve diameter greater than 6.5 mm at the level of L5. Consequently, none of the patients in these two groups could have dural ectasia according to the minor criteria of Ahn et al. In group C, 4% of patients (two of 55) had a nerve root sleeve diameter of 7 mm at the level of L5. In addition, both of these patients proved to have scalloping greater than 3.5 mm and had to be classified as positive for dural ectasia according to the minor criteria.
In group A, 21% of patients (six of 28) proved to have scalloping of more than 3.5 mm at S1, whereas in groups B and C, 14% (one of seven) and 25% (14 of 55), respectively, met this criterion.
Evaluation of Dural Ectasia: Criteria by Fattori et al
By using the criteria developed by Fattori et al (14) to evaluate the patients with Marfan syndrome (group A), the patients likely to have Marfan syndrome (group B), and the patients without suspicion of Marfan syndrome (group C), we found that 93% of patients (26 of 28) in group A and 86% of patients (six of seven) in group B had dural ectasia. In group C (control group), 44% of patients (24 of 55) met the criteria for dural ectasia (Table 4).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Oosterhof et al (16) concluded from their study results that an abnormal dural sac ratio at either L3 or S1 can be used to identify dural ectasia with 95% sensitivity and 98% specificity. Yet the mean dural sac ratio at each level of the lumbar spine was significantly higher in patients with Marfan syndrome than in their control subjects (P < .001 at all levels). The patients in their study population ranged in age from 18 to 47 years, with a mean age of 30.9 years. In our study, the dural sac ratio in patients with Marfan syndrome was significantly higher compared with that in groups B and C only at L5 (P = .003) and S1 (P < .001). In contrast, at levels L1 through L4, we could not find significant differences between the three groups. At the level of L5, the mean dural sac ratio in patients with Marfan syndrome was 0.57 mm in our study and was 0.56 mm in the study presented by Oosterhof et al. At the level of S1, however, Oosterhof et al could demonstrate a dural sac ratio of 0.88 mm, whereas in our group of young patients with Marfan syndrome, the dural sac ratio was only 0.69 mm. The predominant presence of dural ectasia at the lowest vertebra supports the theory that development of dural ectasia is influenced by hydrostatic pressure (5). This theory is supported by our results, in which younger patients demonstrated a significant difference only at the two lowest levels. The significant difference between groups A and B may be caused by a mild expression of Marfan syndrome or by the absence of this disease, because by using this criterion, none of the patients in group B reached a dural sac ratio at L5 or S1 that was comparable with the mean dural sac ratio in group A. Therefore, calculation of a ratio between the dural sac diameter and the vertebral body diameter is most likely to create an age- and BMI-independent parameter, and our results suggest that the dural sac ratio at these levels can be used as a parameter for early diagnosis of dural ectasia. Cut-off values of 0.42 at the level of L5 and 0.51 at the level of S1 offer the best discrimination for the presence or absence of dural ectasia (by assuming a binomial distribution).
Moreover, another parameter showed a significant difference between patients with Marfan syndrome and those in the control group in our study: sagittal dural sac width at S1 greater than that at L4. This parameter, described by Ahn et al (15), can be easily and reliably measured in a routine clinical setting on sagittal T1- or T2-weighted MR images. If this parameter were used exclusively, 32% of patients (nine of 28) in group A and only 2% of patients (one of 55) in group C would have been classified as having dural ectasia. When taking into account that in other studies the prevalence of dural ectasia in patients with clinically proved Marfan syndrome was between 93% and 95%, there is a notable difference in our results. This can probably be explained by the differences in patient age between our study of children, adolescents, and young adults and the quoted studies, in which participants had a mean age of 32.6 years (14) and 30.9 years (16).
By using all the major and minor criteria of Ahn et al (15) for the assessment of dural ectasia, we found that the value of anterior sacral meningocele as a major criterion seems to be limited in children, adolescents, and young adults, because this rare criterion was not observed in any of our patients. According to the Ahn et al criteria, dural ectasia exists when two minor criteria are met. In our study, a nerve root sleeve diameter greater than 6.5 mm at the L5 level could not be observed in groups A and B. Considering this finding, the results concerning scalloping as the second minor criterion are of limited value for the evaluation of dural ectasia. Furthermore, the results of our study indicate that scalloping at the levels of L5 and S1 is not an appropriate criterion to distinguish between patients with and those without dural ectasia. As already mentioned, sagittal dural sac width at S1 greater than that at L4, a major criterion according to Ahn et al, is the sole exception of the criteria in this system.
Fattori et al (14) defined qualitative criteria to diagnose dural ectasia by evaluating the prevalence of different features. In comparing the studies of Fattori et al (14) and Oosterhof et al (16), the prevalence of dural ectasia in Marfan syndrome was slightly higher when quantitative criteria were preferred: 95% versus 93%. In both studies, MR imaging was used to evaluate dural ectasia. Comparable to those results, by using qualitative criteria in group A in our study, 93% of our patients (26 of 28) with Marfan syndrome proved to have dural ectasia. In addition, in the study by Fattori et al, dural ectasia was not identified in any of the 100 volunteers in the control group, whereas in our study, 44% of patients in the control group had positive results for dural ectasia when these qualitative criteria were used. According to the theory that development of dural ectasia is influenced by hydrostatic pressure, the prevalence of dural ectasia is supposed to be lower in children, adolescents, and young adults than in adult patients with Marfan syndrome. In our experience, qualitative criteria are of limited value, not only in younger patients, especially when methods of measurement are available. It seems to be in the nature of a staging system that a measured value—scalloping, for example—is more reliable and comparable than is a visual impression.
A limitation of our study was that a reference standard for the evaluation of dural ectasia was missing, as in all studies we have compared with ours. In addition, the dural volume was not measured in this study. However, with regard to the purpose of our study, this aspect does not seem to be necessary because the value of the published criteria for the assessment of dural ectasia in patients with Marfan syndrome was determined and compared with a control group. An additional limitation of our study may be that the patients in the control group (group C) were an average of 1.4 years younger than were those in group A and 0.3 years older than were those in group B, so that pair-to-pair matches could not be performed. Hence, the age- and BMI-dependency of all presented results was evaluated and showed no serious influence on the results. At this point, the population of the control group in our study is too small to present reference values for every criterion according to the age or BMI of young patients, but a prospective study has already been initiated at our institution. The population of group B, especially, is relatively small, so that the evaluation of this group is limited. Nevertheless, it was worthwhile to include this group in the study to show the difficulties in adequately diagnosing dural ectasia in these borderline patients. Therefore, the retrospective results of this study need to be validated prospectively. The images were evaluated by two experienced radiologists working in consensus, and no independent individual data were collected. This is a limitation of our study and should be avoided in future studies dealing with this topic. Regardless of this limitation, the conclusion of this study is not confined, because there was a reliable and reproducible analysis method.
In conclusion, only the dural sac ratio at the L5 and S1 levels and a sagittal dural sac diameter at S1 greater than that at L4 could be considered useful criteria for the assessment of dural ectasia in children, adolescents, and young adults.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Authors stated no financial relationship to disclose.
Author contributions: Guarantor of integrity of entire study, C.R.H.; study concepts, C.R.H., F.W.; study design, C.R.H., V.S.; literature research, C.R.H., M.C.C.; clinical studies, C.R.H., F.W., J.K., O.W.; data acquisition, C.R.H., F.W., M.C.C.; data analysis/interpretation, C.R.H., F.W., V.S., M.C.C.; statistical analysis, V.S.; manuscript preparation, C.R.H., M.C.C., F.W.; manuscript definition of intellectual content, C.R.H., F.W., G.A.; manuscript editing, C.R.H.; manuscript revision/review, G.A., M.C.C., J.K., O.W., V.S.; manuscript final version approval, C.R.H., V.S., G.A.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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