An important modality for the assessment of the function of the testis is the measurement of its volume [1,2,3,4,5]. It is more challenging, however, to accurately measure the volume of smaller testes such as those of children or some men with infertility due to testicular failure, because of interference which may arise from the scrotal skin and tissues around the testis . The Prader orchidometer is commonly used in the clinical assessment of testicular volume, due to its relative ease, low cost and reproducibility [14, 15]. Some workers have shown that the orchidometer does overestimate the testicular volume measured, especially in small testes, as the scrotal skin, the epididymis and other peritesticular tissues are included in the measurement [11, 19, 20]. Testicular volume studies in an animal model using the orchidometer have shown that volume overestimations of up to 30% may occur in testes whose actual volumes ranged from between 1 and 15 mls . The accuracy of testicular volume measured with the orchidometer has, however, been shown to be influenced by the observer’s experience [4, 15, 22]. There is no consensus, however, on whether or not the reliability of the testicular volumes measured with the Prader orchidometer varies with the age of the subject . Although the median age of the patients in this study was 3 years, their ages varied widely between 18 days and 13 years.
Although the method of testicular volume measurement judged to be the most accurate is still being debated, there are many who believe that ultrasonography (US) gives the most accurate in situ estimation of the volume of the testis [4, 12, 13, 18]. It is commonly believed that US gives an excellent assessment of the volume of the testis which is reproducible, accurate and objective . Testicular volume determination by US is calculated from measured parameters (Length[L], Width[W] and Height[H]) of the testis gotten by using a high-frequency (7.5 MHz) transducer to scan the testis in multiple planes [1, 4, 12, 13]. The testis is believed to be an approximate ellipsoid, and its volume is thus calculated from inputting its measured parameters (Length, Width and Height) into various formulae [1, 12, 13]. In a study by Paltiel et al., which compared the testicular volumes gotten using various formulae (the formula for a prolate spheroid: L × W2 × 0.52; the formula for a prolate ellipsoid: L × W × H × 0.52; the Lambert empiric formula: L × W × H × 0.71) to that gotten by water displacement (true testicular volume) in a canine model, it was shown that the empiric formula of Lambert approximated most closely to the true testicular volume . A study in human adults who underwent orchidectomy for the management of carcinoma of the prostate showed a similar result . Lin et al., however, have shown in their study that the empiric formula of Lambert may not be the most accurate formula for the estimation of testicular volume in smaller testes . All the volume calculations carried out in this present study employed the empiric formula of Lambert.
Ultrasound-measured testicular volume is dependent on the experience of the operator, as inter-observer and intra-observer variations have been reported . Although it has fewer problems with soft tissue interference, the testes being elastic in nature and easily deformed by the applied transducer pressure could give a falsely larger length and a wider width during ultrasonography [14, 18]. Also given that the testis is not perfectly an ellipsoid and that its shape is not regular, application of the ellipsoid formulae in its volume calculations may not yield an accurate figure . Cha et al. showed that US underestimated testicular volume in children with statistical significance . The similar results have also been reported in adults for the three commonly used US formulae for the calculation of testicular volume . An additional advantage, however, in the use of US in testicular volume assessment is that it provides information on intrascrotal and intratesticular pathologies, thus making it complimentary to the orchidometer in testicular function assessment.
Various authors have shown in their studies that testicular volumes obtained using the orchidometer correlated well with volumes obtained using US and with the true testicular volume obtained by water displacement [4, 11,12,13,14, 21, 26, 27]. This present study also has shown that testicular volumes measured with the Prader orchidometer in children correlated significantly with volumes measured by US and with intra-operative caliper measurements. In this study, the testicular volumes estimated by the Prader orchidometer for both the left and the right testicles were significantly larger than those measured using US. This is, however, at variance with the findings of Tatsunami et al., who compared testicular volume measurements in adult (age range 20–26 years) volunteers . Intra-operative caliper-measured mean testicular volumes were lower than those measured by US and the orchidometer for both the right and left testes. This may be because the caliper measurements were only taken on the testes on the side of the pathology which may have affected the volumes. Adaletli et al. had earlier documented that flattening of the testes was noticed in 22% of children with hydrocoeles, and that 8% of them had testicular atrophy .
Also our data showed that for both US and orchidometer measurements, the right testicular volumes were larger than the left; however, there was no statistical significance. This may be explained by our small sample size . Similar findings have been reported by other workers [26, 27]. The observed difference between the volumes of the right and left testes may be explained by the more prominent pampiniform plexus and more sluggish venous drainage on the left side (due to the perpendicular drainage of the left testicular vein into the left renal vein) which results in a warmer and smaller ipsilateral testis [20, 27].