Testicular Volume in a Cohort of Prepubertal Indian Children.

CONTEXT: There are orchidometer-based testicular volume nomograms for Indian children; however, accurate and reliable values measured by ultrasound are lacking. AIMS: The aim of this study was to (1) measure the testicular volumes of boys from birth to 8 years and generate reference values and (2) to identify factors if any that may influence variation in testicular volumes. SETTINGS AND
DESIGN: This was a prospective observational study conducted on 320 children in the Department of Pediatric Surgery, Christian Medical College, Vellore, India. SUBJECTS AND METHODS: A total of 320 boys without any genital abnormalities were studied. The testes were scanned using a linear transducer, and the length, width, and depth of each testis were recorded. Testicular volume was calculated using Lambert's equation - length × width × depth × 0.71. STATISTICAL ANALYSIS USED: Mean testicular volumes and standard deviation for every year of age were calculated. The centile values for testicular volume were computed using R software.
RESULTS: Age-specific nomogram of each testis was created separately. Interobserver variability of the measurement was shown to be up to 0.3 ml. No difference was demonstrated in the testicular volumes between the right and left testis. No correlation was found between body weight and body mass index with testicular volume. From the data on differences in size between the two sides, a volume differential index of 27% corresponds to the 95th centile.
CONCLUSIONS: Reference values have been created for testicular volumes in prepubertal Indian children that could be used to assess the effects of disease and surgical interventions in this age group.

INTRODUCTION

Accurate determination of testicular volume is an important tool in the clinical assessment and follow-up of conditions such as disorders of puberty, undescended testis, and varicocele.[12] Ultrasonographic measurement of testicular volume is now considered the gold standard as they are highly accurate and precise.[3456]

Various reported studies in Indian children have used the Prader's orchidometer[7] and water-displacement technique[8] to measure testicular volume, however, none have reference values for ultrasonography which is the gold standard. This study aims to obtain ultrasonographic reference values of testicular volumes for Indian children from birth to 8 years of age.

SUBJECTS AND METHODS

This prospective observational study was conducted on 320 children from March 2015 to February 2016. All inpatient and outpatient children from birth to 8 years of age were considered for the study. Children with a history of groin surgery, inguinal hernia, hydrocele, undescended testis, varicocele, testicular tumors, torsion testes, disorders of sexual differentiation, chronic liver disease, and failure to thrive were excluded from the study. The minimum sample size required for <4 years of age was 35 each per year of age, and for 4–8 years was 45 each per year of age. The reason attributed to larger sample size at higher ages was increasing variance.

Children were stratified into different age groups according to their date of birth. Children aged 1 day–365 days were grouped as age one, 366–730 days were grouped as age two, 731 days–1095 days as age three, etc. A detailed explanation of the nature of the study was provided to the caregivers, and an informed consent in their own language was obtained. The study design and methodology were approved by the Ethics Committee and the Institutional Review Board (Ref-IRB Min No 9342 dated March 03, 2015).

Sonographic assessment of testicular volume was performed only by the principal investigator (PI), thereby negating the interobserver bias. The instrument used was Sonosite M-turbo portable ultrasound machine with the L25x/13-6 MHz, 25-mm linear array transducer. The procedure was performed with adequate privacy, in supine position with the thighs apart. Distractions such as toys and colorful objects aided in the process of performing the scan. Scanning was performed using light pressure to avoid distorting the testicular shape. Separate axial and longitudinal images of each testis were obtained, and the largest dimension was taken and used for calculation of testicular volume. Testicular volumes were calculated using Lambert's formula (length [L] × width [W] × height [H] × 0.71) as it is considered to be the most accurate and precise.[910]

On analysis, in modeling, log-normal distribution was assumed to get over any skewness. Cubic spline smoothing was done using the generalized additive models for location scale and shape method which in turn uses the R software (University of Auckland, New Zealand).[11] The 5th, 10th, 25th, 50th, 75th, 90th, and 95th centiles for testicular volume, mean, and standard deviations (SDs) were computed using R software. These were then represented on graphs. In addition, testicular volume was compared with weight and body mass index (BMI) using the paired t-test, and the significance of these correlations was calculated using the two-tailed significance test (P < 0.05 taken to be statistically significant).

To validate the ultrasound findings of the PI, ten boys were chosen at random and ultrasonographic measurement of the testicular volume was done separately by a consultant radiologist and the PI. The findings of the PI and the radiologist were then compared to calculate the level of agreement between them.

RESULTS

The volume of the right and left testis for each individual was measured. The right testis volume ranged from 0.49 ml to 2.07 ml, and the left testis volume ranged from 0.47 ml to 2.04 ml. There was no statistically significant difference between the volumes of the right and left testis for all age groups. Individual and combined nomograms of testicular volumes ranging between the 5th and 95th centile were made [Figures 1–3. The centile values, mean, and SDs for the right and left testicular volumes along with the combined average are given below [Tables 1–Table 3].

Figure 1

Testicular volume distribution in the right testis across various age groups

Figure 3

Combined testicular volume nomogram from birth to 8 years

Table 1

Centile, mean, and standard deviation values according to the age for the right testis

Right testes
	n	C5	C10	C25	C50	C75	C90	C95	Mean	SD
1	35	0.59	0.63	0.72	0.82	0.94	1.06	1.14	0.84	0.17
2	35	0.58	0.62	0.70	0.80	0.92	1.04	1.12	0.82	0.15
3	35	0.57	0.61	0.69	0.79	0.91	1.03	1.10	0.80	0.15
4	35	0.59	0.63	0.71	0.82	0.94	1.06	1.14	0.82	0.20
5	45	0.63	0.68	0.77	0.88	1.00	1.13	1.22	0.90	0.16
6	45	0.67	0.72	0.82	0.94	1.07	1.21	1.30	0.96	0.22
7	45	0.71	0.77	0.87	0.99	1.13	1.28	1.38	1.00	0.16
8	45	0.76	0.82	0.92	1.06	1.21	1.36	1.47	1.08	0.26

SD: Standard deviation

Table 3

Combined centile, mean, and standard deviation values according to the age for both testis

Combined (average of right and left testes)
	n	C5	C10	C25	C50	C75	C90	C95	Mean	SD
1	35	0.60	0.65	0.72	0.82	0.93	1.04	1.12	0.83	0.13
2	35	0.60	0.64	0.72	0.82	0.93	1.04	1.11	0.84	0.16
3	35	0.59	0.63	0.71	0.81	0.91	1.02	1.10	0.81	0.14
4	35	0.60	0.64	0.72	0.82	0.93	1.04	1.11	0.82	0.19
5	45	0.64	0.69	0.77	0.87	0.99	1.11	1.19	0.89	0.17
6	45	0.69	0.74	0.83	0.94	1.06	1.19	1.27	0.96	0.19
7	45	0.73	0.78	0.88	0.99	1.13	1.26	1.35	1.00	0.15
8	45	0.77	0.83	0.93	1.05	1.20	1.34	1.43	1.08	0.24

SD: Standard deviation

Testicular volume distribution in the left testis across various age groups

In addition, the presence of any correlation between testicular volume and variables, such as weight of the child and BMI, was studied. It was found that there was no statistically significant correlation between the weight or BMI of boys and testicular volume.

When comparing the measurements made by the PI and the radiologist, a minimum and maximum volume difference of 0.07 ml and 0.38 ml, respectively, was calculated. This difference in measurements between the PI and radiologist was not statistically significant as the inter-rater agreement was excellent and the values were within ± 2SD.

Although no statistically significant difference was found between the testicular volumes of the right and left side in our study, we sought to use the difference in volumes between the sides to create an index that could be used to identify children with potential testicular diseases and to assess postoperative testicular outcomes. The volume differential index (VDI) was thus calculated as the difference in volumes between the two testes/volume of the larger testis × 100. It was expressed as a percentage and then plotted on a graph [Figure 4]. Mean and SDs for VDI were calculated, and from the graph, it was extrapolated that ± 2SD from the mean would be 27%. Thus, a VDI of more than 27% may be considered as a pointer to abnormal testicular function needing further evaluation.

Figure 4

Mean difference in testicular volume and volume differential index

DISCUSSION

Testicular volume measurement is an important tool in diagnosing a variety of medical and surgical conditions. Men with infertility usually undergo a thorough assessment of testicular volume along with semen analysis, as it correlates well with the functioning of the testis.[1213] Studies have shown that men with infertility who record a subnormal sperm density usually have a combined/total testicular volume of <30 ml whereas men who had azoospermia and severe oligospermia had combined/total testicular volumes <10 ml and 20 ml, respectively.[12]

Volume measurements also aid in making important clinical decisions regarding the surgical intervention. In boys with varicocele, a difference in volume of 20%–25% between the two testes has been used as a marker for surgical correction. As semen analysis in the younger age group is considered unethical and psychologically incorrect, the measurement of testicular volume can help in deciding the need for surgery.[4] Testicular volume measurement has also been useful in the postoperative monitoring and long-term follow-up of the patients after surgery for varicocele and undescended testis.[14]

A precise determination of testicular volume is of paramount importance in evaluating patients who suffer from various disease conditions that affect the growth and function of the testis. Although these nomograms exist for children of the Western population, reliable nomograms for Indian or Asian children are not available. The few Indian studies done in the past for testicular volume nomograms have used the Prader's orchidometer which gives a less than accurate measure, and the age of children recruited were always 8 years and above. Hence, obtaining reliable nomograms of testicular volume for Indian children <8 years of age has become imperative.

The study by Kuijper et al.[15] created nomograms for boys across various ethnic groups from birth to 6 years of age laying special emphasis on infants. Testicular volumes in this study ranged from 0.23 to 0.5 ml. Similarly, in the study conducted by Goede et al.[16] on children between 6 months and 18 years of age, testicular volume for the right testis ranged from 0.23 to 20.23 ml and the left testis from 0.2 to 20.13 ml.

However, in our study, testicular volumes from birth to 8 years of age were higher than other studies.[1516] This can be attributed to the different formulae used in the calculation of testicular volume. Whereas the above-mentioned studies[1516] used the ellipsoid formula in calculating the testicular volume, we used Lambert's formula in this study which has been proven as the most accurate of all formulas after comparison with the water-displacement technique.[910] This technique is based on the Archimedes' principle and is considered to be the gold standard. Here, the testis is bared by excising the cord structures and epididymis. The testis is then immersed in a beaker of water, and the volume of water displaced is recorded as the testicular volume.[17] The requirement of an orchidectomy specimen for this technique makes it unavailable for everyday use.

In addition, an interobserver variation of up to 0.3 ml was recognized between the PI and radiologist which was within ± 2SD. This variation in testicular size can be attributed to technical differences where even the slightest of pressure can distort the shape of the testis and thus its dimensions.[18] However, the volumes obtained in our study at 8 years of age (95th centile volume of 1.4812 ml [L] − 1.4919 ml [R]) were found to be comparable with other Indian studies[78] where the testicular volume at 8 years of age was 1.4 ml.

In our study, we also tried to demonstrate whether there existed any correlation between testicular volume and body weight or BMI. As suggested by previous studies,[1519] no correlation was found. Our study also demonstrated that there is no significant difference in the volumes between the right and left testis (P > 0.05) in concordance with studies from the Western world.[1516] Hence, a combined nomogram of both testes should suffice for a particular age group.

The difference in volume between the two testes was used to create an index that could be used to identify children with potential testicular diseases and use to assess postoperative testicular outcomes. The VDI was thus calculated as the difference in volumes between the two testes/volume of the larger testis × 100 and was expressed as a percentage. The VDI for all boys in our study was calculated and plotted on a graph. The 95th centile or two SDs from the mean were found to be 27%.

The index has many potential benefits. It could be used as a quick guide to identify “normal” boys with no apparent testicular pathology but with an abnormal testicular size. Boys with varicocele on regular follow-up could be offered surgery if the VDI exceeds 27%. In children with undescended testis and varicocele, testicular atrophy can occur either due to the disease process itself or as a consequence of surgery. VDI done both in the preoperative and postoperative periods will help in prognosticating these children.

CONCLUSIONS

Measurement of the testicular volume is a useful tool to assess testicular function. Baseline values for testicular volume have been lacking in Indian children. We have constructed a nomogram of testicular volumes with centiles and SD applicable to Indian children up to 8 years of age.

Testicular VDI of 27% was found to be equivalent to the 95th centile in our study. The index could be the basis for surgery in children with varicocele and also be helpful in assessing postoperative outcomes in varicocele and undescended testis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 2

Centile, mean, and standard deviation values according to the age for the left testis

Left testes
	n	C5	C10	C25	C50	C75	C90	C95	Mean	SD
1	35	0.58	0.63	0.71	0.81	0.93	1.05	1.13	0.82	0.14
2	35	0.59	0.64	0.72	0.82	0.94	1.07	1.15	0.86	0.18
3	35	0.58	0.63	0.71	0.81	0.93	1.05	1.13	0.83	0.16
4	35	0.58	0.63	0.71	0.81	0.93	1.05	1.13	0.82	0.20
5	45	0.62	0.67	0.75	0.86	0.99	1.12	1.20	0.88	0.19
6	45	0.67	0.72	0.81	0.93	1.07	1.21	1.30	0.96	0.17
7	45	0.71	0.77	0.87	0.99	1.14	1.29	1.38	1.01	0.18
8	45	0.75	0.81	0.91	1.05	1.20	1.36	1.46	1.07	0.24

SD: Standard deviation