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Published online before print November 12, 2001, 10.1148/radiol.2221001385
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(Radiology 2002;222:114-119.)
© RSNA, 2001

Experimental Studies

Testicular Volume: Comparison of Orchidometer and US Measurements in Dogs1

Harriet J. Paltiel, MD, David A. Diamond, MD, James Di Canzio, MS, David Zurakowski, PhD, Joseph G. Borer, MD and Anthony Atala, MD

1 From the Departments of Radiology (H.J.P.), Urology (D.A.D., J.G.B., A.A.), Biostatistics (J.D., D.Z.), and Orthopaedic Surgery (D.Z.), Children’s Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115. From the 2000 RSNA scientific assembly. Received August 14, 2000; revision requested September 26; final revision received June 25, 2001; accepted August 1. Address correspondence to H.J.P. (e-mail: harriet.paltiel@tch.harvard.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 STATISTICAL CONSULTANT...
 REFERENCES
 
PURPOSE: To compare the accuracy and precision of orchidometer and ultrasonographic (US) measurements of testicular volume in a canine model.

MATERIALS AND METHODS: Volume measurements of 18 canine testes were obtained by using Prader and Rochester orchidometers. Testes were scanned with two linear-array US transducers with imaging frequencies of 6–13 MHz and 5–10 MHz. For each transducer, testicular volumes were calculated by using three formulas: length (L) x width (W) x height (H) x 0.52, L x W2 x 0.52, and L x W x H x 0.71. Testes were weighed following bilateral orchiectomies. True testicular volume was determined by using the formula volume = weight/density. Paired t tests were used to assess whether mean measurement biases differed significantly from zero. The relationship between true and measured volume was evaluated with a linear regression model.

RESULTS: US volume measurements demonstrated lower variability and better linear fit compared with orchidometry (R2 = 0.75–0.90 vs R2 = 0.14–0.38). The formula L x W x H x 0.71 had the smallest mean bias relative to true volume with use of either transducer over the entire volume range.

CONCLUSION: US methods of testicular volume measurement are more accurate and precise than orchidometry. The formula L x W x H x 0.71 provides a superior estimate of testicular volume and should be used in clinical practice.

Index terms: Animals • Experimental study • Testis, US, 84.12989 • Ultrasound (US), experimental studies, 84.12989


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
 STATISTICAL CONSULTANT...
 REFERENCES
 
Accurate determination of testicular volume is of great potential benefit in the evaluation of patients with a variety of disorders affecting testicular growth and development. Since approximately 70%–80% of testicular mass consists of seminiferous tubules, testicular volume is largely a reflection of spermatogenesis (1). Results of studies in infertile men have shown that testicular volume has a direct correlation with semen profiles. A total testicular volume (ie, sum of the volumes of both testes) of approximately 30 mL is indicative of normal testicular function (2). Currently, a number of measurement techniques are used, including orchidometry and ultrasonography (US).

US is generally recognized as the most accurate means of in situ assessment of testicular volume (3–6), although its acceptance is not universal. It has been stated as recently as 1995 that "the degree of correlation between ultrasonically determined testicular volumes and those measured with an orchidometer depends primarily on the experience of the examiner, and the added expense of US volumetrics is not justified by any theoretical advantage in accuracy" (7). Furthermore, there is a lack of standardization, with different formulas used to calculate volume based on US measurements of testicular length, width, and height (4,8–10).

The aims of our study were (a) to compare the accuracy and precision of orchidometer and US measurements in a canine model by using the two most commonly employed orchidometers, the Prader (11) and the Rochester (12), and (b) to compute testicular volume from US-derived measurements by using three of the most commonly quoted formulas in the literature and to compare the accuracy and precision of these formulas with respect to true volume.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 STATISTICAL CONSULTANT...
 REFERENCES
 
Animals
This study was performed according to a protocol approved by the animal care and use committee of our hospital and conformed to guidelines issued by the National Institutes of Health for care of laboratory animals. We chose a canine model since canine testes are very similar in size and shape to human testes and the scrotum in dogs is easily accessible for palpation and US examination. Nine beagles aged 1 year were used (13). All of the dogs had previously undergone a series of experiments involving bladder and penile function and were scheduled to be sacrificed for organ retrieval. This study was performed immediately prior to sacrifice. The prior experiments performed on these animals did not affect testicular volume or shape.

General anesthesia was induced with intramuscular butorphanol (0.2 mg/kg), acepromazine (0.05 mg/kg), and glycopyrrolate (0.01 mg/kg). Anesthesia was maintained with 2%–5% isoflurane. An endotracheal tube was placed to protect the airway, and one line was placed for intravenous access.

Physical Examination
The dogs were placed in a supine position, and volume measurements were obtained by one of the authors (D.A.D.), a board-certified urologist, by using both the Prader and Rochester orchidometers. The Prader orchidometer consists of 12 solid ellipsoid models ranging in volume from 1 to 25 mL (1–6, 8, 10, 12, 15, 20, and 25 mL), against which the testis is compared (Fig 1a). The Rochester orchidometer consists of 15 punched-out elliptical rings with volumes ranging from 1 to 30 mL (1–6, 8, 10, 12, 14, 16, 19, 22, 26, and 30 mL). Testicular volume was determined by means of snug placement of the ring up to the midportion of the testis (Fig 1b).



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  		Figure 1a. Orchidometry. (a) Photograph of a solid 10-mL Prader orchidometer ellipse adjacent to the right testicle of an anesthetized dog. (b) Photograph of a 14-mL Rochester orchidometer cutout ellipse surrounding the right testicle of an anesthetized dog.

 


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  		Figure 1b. Orchidometry. (a) Photograph of a solid 10-mL Prader orchidometer ellipse adjacent to the right testicle of an anesthetized dog. (b) Photograph of a 14-mL Rochester orchidometer cutout ellipse surrounding the right testicle of an anesthetized dog.

 
US Evaluation
US studies were performed by the first author (H.J.P.), a board-certified pediatric radiologist. The testes were scanned with a US imaging machine (Logiq 700; GE Medical Systems, Milwaukee, Wis) and linear-array transducers with frequencies of 6–13 MHz and 5–10 MHz. The transducer power output was set below 100 mW/cm2 in accordance with the U.S. Food and Drug Administration’s acoustic output guidelines for US studies.

Gray-scale images of the testes were obtained in transverse and longitudinal planes. Multiple focal zones were used during image acquisition. Scanning was performed by using light pressure to avoid a distortion of testicular shape. Measurements of testicular length, width, and height were obtained by using electronic calipers (Fig 2).



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  		Figure 2. US testicular volume measurement. Sagittal US image of a canine testis. The calipers measure testicular length (A) and height (B).

 
At least three separate transverse and longitudinal images of each testis were obtained with both transducers. The largest measurement obtained for each testicular dimension was recorded and used for volume calculation and statistical analysis. An effort was made to avoid inclusion of the epididymis when performing testicular measurements.

Testicular volumes were calculated by using three formulas: (a) the formula for an ellipsoid: length (L) x width (W) x height (H) x 0.52; (b) the formula for a prolate spheroid: L x W2 x 0.52; and (c) the empiric formula of Lambert (8): L x W x H x 0.71.

True Testicular Volume Determination
Animals were sacrificed with an intravenous overdose of pentobarbital (100 mg/kg; 1 mL/4.5 kg). Bilateral orchiectomies were performed immediately following euthanasia by two of the authors (D.A.D., J.G.B.), both board-certified urologists, and the epididymides were removed. Each testis was weighed on a balance (model AB204; Mettler-Toledo, Greisensee, Switzerland).

True testicular volume was calculated by using the formula volume = weight/density, where density equaled 1.038 gm/mL (14), with values rounded to the nearest 0.1 mL. Handelsman and Staraj (14) determined that the mean testicular density in humans is 1.038 gm/mL, with a standard error of the mean of plus or minus 0.001 gm/mL. This measurement was derived from data collected from 1,056 autopsies performed in men ranging in age at death from 18 to 96 years (14). The authors found that mean testicular density was not altered over a wide range of testicular sizes, ages, or disease states. We believe that we were justified in using the same density measurement of 1.038 gm/mL since the testicular anatomic and histologic features in humans and dogs are very similar. Rivkees et al (3) used a density value of 1.04 gm/mL in their experimental study of testicular volume in dogs and calves.

Statistical Analyses
Nine volume measurements were obtained for each of the 18 testes: two orchidometer assessments (Prader and Rochester), six US calculations (three formulas for each of the two US transducers), and weight determination followed by calculation of true volume, as described earlier. Paired t tests were used to determine if the orchidometer and US volume measurements differed significantly from the true volume. The relationship between each measurement technique and true testicular volume was evaluated by using linear regression analysis, with true volume as the independent variable and the orchidometer or US measurement as the dependent variable. For each regression line, 95% confidence bands and a 45° (equivalence) line were included to provide a reference for comparison with the no-intercept regression. The R2 statistic provided a measure of the strength of the linear association.

The estimated slope parameter was tested against the theoretical value of 1, and the intercept was tested against a value of 0 by using a one-sample Student t test. A slope significantly different from 1 indicated that the difference relative to true testicular volume was not consistent over the range of volumes measured but rather varied with the magnitude of the volume. A two-tailed P value of less than .05 was considered statistically significant.

Paired t tests were used to compare differences in volume measurements obtained with the two US transducers for each of the three US formulas and differences in volume measurements obtained by using formulas 1 and 2. The R2 values obtained for each of the six US methods were compared for statistically significant differences by using Fisher z-transformation (15). All statistical analyses were performed by using a computer software package (SAS, version 6.12; SAS Institute, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 STATISTICAL CONSULTANT...
 REFERENCES
 
Testicular weights varied between 6.8 and 12.92 gm, with a mean weight of 8.52 gm. True testicular volume varied between 6.6 and 12.4 mL, with a mean volume of 8.2 mL. The Prader orchidometer and four of the six US techniques produced testicular volume measurements that were significantly different from true volume (P < .05 in all cases; Table). The largest mean biases were observed with US formula 1 (L x W x H x 0.52), which underestimated true volume by 2.1 mL (36%) and 1.9 mL (31%) with the 6–13-MHz and 5–10-MHz transducers, respectively. The Prader orchidometer overestimated true volume by 1.6 mL (12%), while US formula 2 (L x W2 x 0.52) used with measurements from the 5–10-MHz transducer overestimated true volume by 1.1 mL (11%). The SDs were much higher for the orchidometers (Prader SD = 2.5 mL; Rochester SD = 2.2 mL) than for any of the US methods (SD = 0.6–1.0 mL).


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  		Comparison of Testicular Measurement Technique Values with True Testicular Volume

 
Regression analysis results indicated that all US methods showed a stronger linear relationship with true volume (R2 = 0.75–0.90; P < .001) than either the Prader orchidometer (R2 = 0.14; P = .12) or the Rochester orchidometer (R2 = 0.38; P = .007). The slope for US formula 1 with use of either transducer was significantly smaller than 1 (P < .01), indicating that this method underestimated the true volume of larger testes to a greater degree than it did the true volume of smaller ones. With both transducers, US formulas 1 (L x W x H x 0.52) and 3 (L x W x H x 0.71) had larger R2 values than US formula 2 (L x W2 x 0.52). However, there were no statistically significant differences between the R2 values of any of the US methods (P > .20).

There was no statistically significant difference between volume measurements obtained with the 6–13-MHz transducer and those obtained with the 5–10-MHz transducer using formula 1 or formula 3 (P > .12). However, there was a statistically significant difference between the two transducers when formula 2 was used to calculate volume (P = .005). There was also a statistically significant difference (P < .001) between obtained volumes when formulas 1 and 2 were compared—viz, L x W x H x 0.52 versus L x W2 x 0.52—regardless of which transducer was used.

US formula 3 had the smallest mean difference from true volume for both transducers (Table). Plots illustrating the relationship of orchidometer and US measurements to true testicular volume are shown in Figure 3.



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  		Figure 3a. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3b. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3c. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3d. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3e. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3f. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3g. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 


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  		Figure 3h. Graphs illustrate comparison of true and measured testicular volumes. The straight dashed lines indicate the theoretical linear relationship obtained from regression parameters. The curved dashed lines represent the 95% confidence bands. The solid lines denote equivalence and are included for comparison. (a) Comparison of true testicular volume with volume measured with the Prader orchidometer, which tended to overestimate true volume. (b) Comparison of true testicular volume with volume measured with the Rochester orchidometer, which tended to overestimate true volume. (c) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (d) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W2 x 0.52. True volume tended to be overestimated. (e) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 6-13-MHz transducer and the formula L x W x H x 0.71. Overall, there was no significant overestimation or underestimation of true volume. (f) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.52. True volume was consistently underestimated. (g) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W2 x 0.52. True volume was consistently overestimated. (h) Comparison of true testicular volume with volume calculated from US measurements obtained by using the 5-10-MHz transducer and the formula L x W x H x 0.71. True volume was generally overestimated.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
STATISTICAL CONSULTANT...
 REFERENCES
 
Determination of testicular volume is important in assessing pubertal development and the effects of illness and treatment on reproductive function. Although it might be adequate in some clinical settings to classify testicular size as small, medium, or large, greater accuracy and precision are required when closely following changes in pubertal status, monitoring testicular involvement by pathologic processes such as varicocele or malignancy, and evaluating the effect of chemotherapeutic or hormonal agents on the testes. Testicular enlargement is the earliest sign of the pubertal gonadotropin elevation in boys, and a testicular volume of 4 mL or greater is used as a clinical marker for the onset of puberty (16). Results of studies in infertile men have also shown that testicular volume is directly correlated to semen profiles. In a study of 486 Japanese male patients, Arai et al (2) documented a sperm density below normal limits in those patients with a total testicular volume of less than 30 mL. Patients with a total testicular volume of less than 10 mL were azoospermic, while total volumes of less than 20 mL were associated with severe oligozoospermia.

In the past, attempts were made to improve clinical assessment of testicular volume by means of a variety of orchidometers (9,11,12). To our knowledge, there have been only two published studies that have compared orchidometer measurements of testicular volume with true volume. Takihara et al (12) evaluated the accuracy of the Rochester orchidometer by comparing measurements of 26 testes with actual volumes determined by means of water displacement and found a correlation coefficient of 0.81. Rivkees et al (3) used an animal model to assess the accuracy of Prader orchidometer measurements compared with true volumes determined by means of water displacement or weight (with weight converted to volume by using the formula volume = weight/density). They found that mean orchidometer measurements exceeded true testicular volume by nearly 30% when testis size ranged from 1.0 to 15.0 mL but approximated true volume when testes were 20 mL or larger.

The theoretical advantage of US over manual methods of testicular volume assessment lies in its ability to enable one to distinguish the testis from the adjacent soft tissues. The presence of the epididymis may prevent an accurate clinical assessment of testicular volume, as may the thickness of the scrotal skin and subcutaneous tissues. Recent studies have used US measurements of testicular volume as the standard to which clinical measurements were compared (3–6,17–20). However, only four of these investigations addressed the issue of the accuracy and precision of US measurements of testicular volume (3–5,17).

Various formulas for calculating testicular volume have been used, but no attempts have been made to directly compare their accuracy and precision with each other. Behre et al (4) compared measurements in 15 patients obtained with two different US machines. One machine automatically calculated volume by using the formula L x W x H x 0.52, while the other used the formula L x W2 x 0.52. There was no statistically significant difference between the mean calculated testicular volumes obtained by using the two methods (4). A sector US probe was employed in four studies (3–5,19), while the transducer type was not specified in one publication (20). Current recommendations for scrotal US include the use of a linear or curved linear transducer (21). The advantage of recent US transducers with multiple focal zones is that the accuracy of distance measurements can be optimized for both the near and far imaging fields.

In several studies where volume determinations were made by means of water displacement of human or animal testes, either the epididymides were not removed (3) or no mention was made of them (5,12), so that the "true" testicular volume measurement may have included the epididymis as well. Costabile et al (17) established the accuracy of their US measurements by scanning a series of testicular-shaped ellipsoids of known volume (1–25 mL) in a blinded manner using a 5.0- or 7.0-MHz linear transducer with a gel standoff pad. Although US was found to be highly accurate, the data are difficult to fully evaluate since the number of models and their individual volumes are not stated. Thus, the wide variations in reported examination technique, volume calculation, and determination of "true" testicular volume make an assessment of the literature problematic. Furthermore, orchidometers are still widely employed by urologists and endocrinologists. Our clinical colleagues continue to question the need for US measurements, attributing the lack of correlation with orchidometer measurements to the inexperience of the examiner (7).

In our study, US measurements were clearly superior to both the Prader and Rochester orchidometer measurements, as reflected by measurements closer to true volume and higher R2 values from the regression models. All three US formulas showed strong linear relationships with true volume, and there were no statistically significant differences between their R2 values. There were no statistically significant differences in volume measurements obtained with either transducer with use of formula 1 or 3, whereas use of formula 2 resulted in statistically significant differences in calculated volumes between transducers. These findings imply that three-dimensional measurements are essential for optimizing precision.

Our study data demonstrated equivalent precision of measurements obtained with either transducer with use of the formula L x W x H and correction factors of 0.52 or 0.71. Since formulas 1 and 3 are proportional, it was predictable that their regression parameters would be different. Formula 3, L x W x H x 0.71, was the most accurate, having the smallest mean differences from true volume. Thus, the correction factor of 0.71 appears to be preferable to the more commonly referenced factor of 0.52.

Our study was limited by the small number of animals and the fact that the shape of the canine testis may differ slightly from that of the human. However, the parameters studied in this report were based on testicular volume measurements, not testicular shape. Testes are compressible, and during both manual manipulation and US examination, their dimensions may be distorted. In addition, the axis of the testis may become oblique to the US beam instead of perpendicular, as presumed when employing the ellipsoid and prolate spheroid volume formulas.

In conclusion, US methods of testicular volume measurement are more accurate and more precise than orchidometry. Although the formula L x W x H x 0.71 was the most accurate for determining testicular volume, there was no statistically significant difference in precision among the three US formulas.

Practical application: US methods of testicular volume determination are more accurate and more precise than two of the most commonly employed clinical measuring devices, the Prader and Rochester orchidometers. The volume formula L x W x H x 0.71 provides a superior estimate of testicular volume and should be used in clinical practice.


   STATISTICAL CONSULTANT COMMENTARY
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 STATISTICAL CONSULTANT...
REFERENCES
 
This article adds to the statistical evidence that testicular volume can be accurately and precisely measured by using the empiric formula suggested by Lambert (8). The authors directly assessed the accuracy and precision of various measurement techniques by means of comparison with a calculated true volume.

A good measurement would match the true volumes almost exactly, allowing for some random variation and a small degree of measurement error in the true estimate. When plotted, the scatter points would fall along the 45° line—that is, the line with unit slope and zero intercept. Deviations from this line or wide variation around it reflects deficiencies in the studied measure. The authors tested that the slope of the regression line was equal to 1, evaluated the intercept, and displayed the R2 value, the proportion of measured volume variation explained by regressing on the true volumes. Accuracy, or lack of bias, is measured on the basis of how much the slope and intercept deviate from 1 and 0, respectively. The graphs in Figure 3 provide an excellent visual test for bias. When any part of the 45° line falls outside of the 95% confidence bounds, there is significant statistical evidence that the measure is not accurate. That is, one may conclude that either the slope is not 1 or the intercept is not 0, or both. Precision may be measured by using the R2 statistic. A high R2 value corresponds to small variation around the regression line. By using these techniques, the authors showed that the US formula L x W x H x 0.71 performs better than the alternatives.


   FOOTNOTES
 
Author contributions: Guarantor of integrity of entire study, H.J.P.; study concepts and design, H.J.P., A.A., D.A.D.; literature research, H.J.P.; experimental studies, H.J.P., J.G.B., D.A.D.; data acquisition, H.J.P.; data analysis/interpretation, H.J.P., J.D., D.Z.; statistical analysis, J.D., D.Z.; manuscript preparation, H.J.P.; manuscript definition of intellectual content, H.J.P., D.A.D.; manuscript editing and revision/review, all authors; manuscript final version approval, H.J.P., D.Z.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 STATISTICAL CONSULTANT...
 REFERENCES
 

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