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Comparison of testicular volume differential calculations in adolescents with varicoceles
Journal of Pediatric Urology (2014) 10, 396e398
Comparison of testicular volume differential calculations in adolescents with varicoceles* Matthew S. Christman a,*, Stephen A. Zderic b, Thomas F. Kolon b a Department of Urology, Naval Medical Center San Diego, 34800 Bob Wilson Drive, San Diego, CA 92134, USA b The Children’s Hospital of Philadelphia, Philadelphia, PA, USA
Received 11 October 2013; accepted 19 December 2013
Available online 11 January 2014
KEYWORDS Varicocele; Testicular volume differential; Adolescents; Scrotal ultrasound
Abstract Purpose: We aimed to develop a conversion formula between different calculations for testicular volume asymmetry. Materials and methods: Male adolescents with varicoceles who underwent scrotal ultrasound were studied. Two formulas were analyzed: (1) testicular volume differential, TVDiff Z (RTV e LTV)/(TTV), and (2) atrophy index, AI Z (RTV e LTV)/(RTV). RTV, LTV, and TTV represent the right, left, and total testicular volume. Through transformations and regression a conversion formula between the calculations was derived. Results: Based on 248 ultrasounds, a clear relationship between the two formulas was demonstrated: AI Z ln[(1.97 TVDiff) þ 1], (p < 0.0001). Conclusions: Differential testicular volumes can easily be converted from one formula to another with near-perfect accuracy. The formulas are essentially identical and interchangeable. Published by Elsevier Ltd on behalf of Journal of Pediatric Urology Company.
Abbreviations: TV, testicular volume; AI, atrophy index; TVDiff, testicular volume differential; RTV, right testicular volume; LTV, left testicular volume; TTV, total testicular volumes; ScrUS, scrotal ultrasound/s. * The views expressed in this manuscript are those of the authors and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the United States Government. * Corresponding author. E-mail address: [email protected] (M.S. Christman). 1477-5131/$36 Published by Elsevier Ltd on behalf of Journal of Pediatric Urology Company. http://dx.doi.org/10.1016/j.jpurol.2013.12.007
Testicular differential formulas
397
Introduction Adolescents experience a rapid increase in testicular volume (TV) during puberty, making interpretation of absolute size differences difficult [1]. As a result, right versus left differential TV is used to provide a relative gauge of asymmetry and plays an important, but controversial, role in management of adolescents with varicoceles [2e4]. Adding to the controversy, and creating confusion, is the fact that two formulas have emerged for calculating relative testicular asymmetry [2,4]. This relative difference in TV was originally termed the “atrophy index (AI),” comparing the affected testis to the opposite one [2]. Later, the idea of “TV differential (TVDiff)” was promoted by gauging asymmetry relative to total volume, much like differential renal function calculations [4]. Over time these terms/concepts have been used interchangeably, despite their differing calculations. Glassberg’s commentary called for using a “single standard formula,” which would aid with interpretation of the literature [4]. We hypothesized that a conversion formula could be derived to translate between these two formulas.
Materials and methods An institutional review board-approved retrospective cohort study was conducted on adolescent males with clinical varicoceles who were undergoing active surveillance with scrotal ultrasound (ScrUS). The Lambert formula was used to calculate TV: TV Z 0.71 length width height [5]. Two formulas for calculating testicular asymmetry were studied: (1) TVDiff Z (RTV e LTV)/(TTV), and (2) AI Z (RTV e LTV)/ (RTV). AI was transformed exponentially, followed by linear regression of these transformed values on TVDiff to determine the slope and y-intercept of the resulting straight line relating the two. STATA v12 (StataCorpLP, College Station, TX, USA) was used.
Figure 1 Relationship of testicular volume differential calculations.
said to be “better.” The derived formula therefore allows one to precisely translate the various findings in the literature to one’s native tongue without the raw data that were used to calculate the original asymmetry; all that is needed is the result from the alternative formula. In other words, we can compare apples to “les pommes.” Thomas and Elder [3] advised surgical intervention on those with an AI cut-off of greater than 15%; this would translate into a TVDiff of 8% according to the formula used by Kolon et al. [4] in work detailing asynchronous testicular growth during adolescence. Conversely, when Kolon showed that 71% of the cohort who initially exceeded a 15% TVDiff cut-point subsequently normalized with observation, Elder would view this cut-point as an AI of 26%. The derived formula should be relatively immune to bias, since identical volume observations were used for each paired calculation.
Results
Table 1 Translation between two formulas for relative testicular asymmetry.
A cohort of 73 patients underwent 248 ScrUS. A clear relationship between the two formulas was demonstrated by the equation AI Z ln[(1.97 TVDiff) þ 1], with p < 0.0001 for the model (Fig. 1). The coefficient of determination (R2) was 0.9999, meaning that 99.99% of the variation in AI could be explained solely by TVDiff. Table 1 contains conversion values.
Testicular volume differential [TVDiff] (%)
Atrophy index [AI] (%)
0 3 5 8 10 11 14 15 18 20 21 25 30 35
0 5 10 15 18 20 25 26 30 33 35 40 46 52
Discussion The near-perfect conversion formula illustrates that these two equations are completely synonymous, rather than different concepts or observations. This statement is based on the fact that R2 Z 0.9999. The coefficient of determination is a statistical measure of how well the regression line approximates the real data points; it provides information regarding goodness of fit. A value of one indicates that the regression line fits the data perfectly. Overall performance of these formulas as a predictor of any outcome will therefore be identical; one formula cannot be
TVDiff Z [RTV e LTV]/[TTV]. AI Z [RTV e LTV]/[RTV]. RTV, LTV, TTV are right, left, and total testicular volume.
398
Conclusions Testicular asymmetry can be converted from one formula to another with near-perfect accuracy, and without knowledge of the specific volumes involved in the original calculation. Each formula can be used interchangeably and would perform equally for predicting outcomes, with appropriate attention to differences in analyzed cut-points.
Ethical approval This study was approved by the institutional review board.
Conflict of interest None.
Funding None.
M.S. Christman et al.
References [1] Goede J, Hack WW, Sijstermans K, van der Voort-Doedens LM, Van der Ploeg T, Meij-de Vries A, et al. Normative values for testicular volume measured by ultrasonography in a normal population from infancy to adolescence. Horm Res Paediatr 2011;76:56e64. [2] Paduch DA, Niedzielski J. Repair versus observation in adolescent varicocele: a prospective study. J Urol 1997;158: 1128e32. [3] Thomas JC, Elder JS. Testicular growth arrest and adolescent varicocele: does varicocele size make a difference? J Urol 2002;168:1689e91. [4] Kolon TF, Clement MR, Cartwright L, Bellah R, Carr MC, Canning DA, et al. Transient asynchronous testicular growth in adolescent males with a varicocele. J Urol 2008;180:1111e4. [5] Hsieh ML, Huang ST, Huang HC, Chen Y, Hsu YC. The reliability of ultrasonographic measurements for testicular volume assessment: comparison of three common formulas with true testicular volume. Asian J Androl 2009;11:261e5.
Comparison of testicular volume differential calculations in adolescents with varicoceles* Matthew S. Christman a,*, Stephen A. Zderic b, Thomas F. Kolon b a Department of Urology, Naval Medical Center San Diego, 34800 Bob Wilson Drive, San Diego, CA 92134, USA b The Children’s Hospital of Philadelphia, Philadelphia, PA, USA
Received 11 October 2013; accepted 19 December 2013
Available online 11 January 2014
KEYWORDS Varicocele; Testicular volume differential; Adolescents; Scrotal ultrasound
Abstract Purpose: We aimed to develop a conversion formula between different calculations for testicular volume asymmetry. Materials and methods: Male adolescents with varicoceles who underwent scrotal ultrasound were studied. Two formulas were analyzed: (1) testicular volume differential, TVDiff Z (RTV e LTV)/(TTV), and (2) atrophy index, AI Z (RTV e LTV)/(RTV). RTV, LTV, and TTV represent the right, left, and total testicular volume. Through transformations and regression a conversion formula between the calculations was derived. Results: Based on 248 ultrasounds, a clear relationship between the two formulas was demonstrated: AI Z ln[(1.97 TVDiff) þ 1], (p < 0.0001). Conclusions: Differential testicular volumes can easily be converted from one formula to another with near-perfect accuracy. The formulas are essentially identical and interchangeable. Published by Elsevier Ltd on behalf of Journal of Pediatric Urology Company.
Abbreviations: TV, testicular volume; AI, atrophy index; TVDiff, testicular volume differential; RTV, right testicular volume; LTV, left testicular volume; TTV, total testicular volumes; ScrUS, scrotal ultrasound/s. * The views expressed in this manuscript are those of the authors and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the United States Government. * Corresponding author. E-mail address: [email protected] (M.S. Christman). 1477-5131/$36 Published by Elsevier Ltd on behalf of Journal of Pediatric Urology Company. http://dx.doi.org/10.1016/j.jpurol.2013.12.007
Testicular differential formulas
397
Introduction Adolescents experience a rapid increase in testicular volume (TV) during puberty, making interpretation of absolute size differences difficult [1]. As a result, right versus left differential TV is used to provide a relative gauge of asymmetry and plays an important, but controversial, role in management of adolescents with varicoceles [2e4]. Adding to the controversy, and creating confusion, is the fact that two formulas have emerged for calculating relative testicular asymmetry [2,4]. This relative difference in TV was originally termed the “atrophy index (AI),” comparing the affected testis to the opposite one [2]. Later, the idea of “TV differential (TVDiff)” was promoted by gauging asymmetry relative to total volume, much like differential renal function calculations [4]. Over time these terms/concepts have been used interchangeably, despite their differing calculations. Glassberg’s commentary called for using a “single standard formula,” which would aid with interpretation of the literature [4]. We hypothesized that a conversion formula could be derived to translate between these two formulas.
Materials and methods An institutional review board-approved retrospective cohort study was conducted on adolescent males with clinical varicoceles who were undergoing active surveillance with scrotal ultrasound (ScrUS). The Lambert formula was used to calculate TV: TV Z 0.71 length width height [5]. Two formulas for calculating testicular asymmetry were studied: (1) TVDiff Z (RTV e LTV)/(TTV), and (2) AI Z (RTV e LTV)/ (RTV). AI was transformed exponentially, followed by linear regression of these transformed values on TVDiff to determine the slope and y-intercept of the resulting straight line relating the two. STATA v12 (StataCorpLP, College Station, TX, USA) was used.
Figure 1 Relationship of testicular volume differential calculations.
said to be “better.” The derived formula therefore allows one to precisely translate the various findings in the literature to one’s native tongue without the raw data that were used to calculate the original asymmetry; all that is needed is the result from the alternative formula. In other words, we can compare apples to “les pommes.” Thomas and Elder [3] advised surgical intervention on those with an AI cut-off of greater than 15%; this would translate into a TVDiff of 8% according to the formula used by Kolon et al. [4] in work detailing asynchronous testicular growth during adolescence. Conversely, when Kolon showed that 71% of the cohort who initially exceeded a 15% TVDiff cut-point subsequently normalized with observation, Elder would view this cut-point as an AI of 26%. The derived formula should be relatively immune to bias, since identical volume observations were used for each paired calculation.
Results
Table 1 Translation between two formulas for relative testicular asymmetry.
A cohort of 73 patients underwent 248 ScrUS. A clear relationship between the two formulas was demonstrated by the equation AI Z ln[(1.97 TVDiff) þ 1], with p < 0.0001 for the model (Fig. 1). The coefficient of determination (R2) was 0.9999, meaning that 99.99% of the variation in AI could be explained solely by TVDiff. Table 1 contains conversion values.
Testicular volume differential [TVDiff] (%)
Atrophy index [AI] (%)
0 3 5 8 10 11 14 15 18 20 21 25 30 35
0 5 10 15 18 20 25 26 30 33 35 40 46 52
Discussion The near-perfect conversion formula illustrates that these two equations are completely synonymous, rather than different concepts or observations. This statement is based on the fact that R2 Z 0.9999. The coefficient of determination is a statistical measure of how well the regression line approximates the real data points; it provides information regarding goodness of fit. A value of one indicates that the regression line fits the data perfectly. Overall performance of these formulas as a predictor of any outcome will therefore be identical; one formula cannot be
TVDiff Z [RTV e LTV]/[TTV]. AI Z [RTV e LTV]/[RTV]. RTV, LTV, TTV are right, left, and total testicular volume.
398
Conclusions Testicular asymmetry can be converted from one formula to another with near-perfect accuracy, and without knowledge of the specific volumes involved in the original calculation. Each formula can be used interchangeably and would perform equally for predicting outcomes, with appropriate attention to differences in analyzed cut-points.
Ethical approval This study was approved by the institutional review board.
Conflict of interest None.
Funding None.
M.S. Christman et al.
References [1] Goede J, Hack WW, Sijstermans K, van der Voort-Doedens LM, Van der Ploeg T, Meij-de Vries A, et al. Normative values for testicular volume measured by ultrasonography in a normal population from infancy to adolescence. Horm Res Paediatr 2011;76:56e64. [2] Paduch DA, Niedzielski J. Repair versus observation in adolescent varicocele: a prospective study. J Urol 1997;158: 1128e32. [3] Thomas JC, Elder JS. Testicular growth arrest and adolescent varicocele: does varicocele size make a difference? J Urol 2002;168:1689e91. [4] Kolon TF, Clement MR, Cartwright L, Bellah R, Carr MC, Canning DA, et al. Transient asynchronous testicular growth in adolescent males with a varicocele. J Urol 2008;180:1111e4. [5] Hsieh ML, Huang ST, Huang HC, Chen Y, Hsu YC. The reliability of ultrasonographic measurements for testicular volume assessment: comparison of three common formulas with true testicular volume. Asian J Androl 2009;11:261e5.