Testicular Volume for a 4cm Long Testicle
A 4cm long testicle corresponds to an estimated volume of approximately 15-18 mL, which falls within the normal range and above the 12 mL threshold that defines testicular atrophy. 1
Volume Calculation Method
Use the Lambert formula (Length × Width × Height × 0.71) for the most accurate testicular volume estimation, as recommended by the European Association of Urology. 1, 2
For a 4cm (41mm) length testicle, the typical proportions yield a height of approximately 20-25mm (50-60% of length) and width of similar dimensions. 3
Using these dimensions in the Lambert formula: 40mm × 25mm × 25mm × 0.71 ≈ 17,750 mm³ = approximately 17-18 mL. 1
A Prader orchidometer reading of 15 mL is a reasonable clinical estimate for a 4cm testis, though ultrasound would likely measure 16-18 mL for the same testis due to systematic measurement differences. 1
Clinical Significance of This Volume
Testicular volumes of 15-18 mL are associated with normal spermatogenesis and adequate fertility potential, according to the European Society of Human Reproduction and Embryology. 1
This volume is well above the critical 12 mL threshold below which testes are considered small or atrophic and associated with impaired spermatogenesis and higher risk of intratubular germ cell neoplasia. 4, 1, 3
Mean testicular size at this volume strongly correlates with normal total sperm count and sperm concentration. 1
Important Clinical Caveats
If there is a size discrepancy between testes greater than 2 mL or 20%, further evaluation including ultrasound is warranted to exclude pathology, regardless of absolute volume. 1
In the context of testicular cancer, even normal-sized testes require specific risk stratification: patients with testicular volume <12 mL and/or history of cryptorchidism should be fully informed regarding the risk-benefit ratio for biopsy of the contralateral testis. 4
Contralateral biopsy is not indicated in patients aged >40 years without risk factors (cryptorchidism or volume <12 mL). 4
In men under 30-40 years with testicular volume <12 mL, there is a >34% risk of intratubular germ cell neoplasia in the contralateral testis if testicular cancer is present. 1, 3
Measurement Considerations
The Prader orchidometer is a good surrogate for testicular volume measurement and is easier to perform and more cost-effective than ultrasound in routine clinical practice. 1
High-frequency probes (>10 MHz) should be used if ultrasound measurement is performed to maximize resolution and accurate caliper placement. 1
Avoid using the traditional ellipsoid formula (0.52 coefficient) for clinical decision-making, as it systematically underestimates volume and may lead to inappropriate classification of testicular atrophy. 1