Normal Adult Testicle Length
Yes, the normal adult testicle length of 3.5-5 cm is accurate, corresponding to a volume typically greater than 12-14 mL, with volumes below 12 mL considered atrophic and warranting further investigation. 1, 2
Normal Testicular Dimensions
The normal adult testicular size can be expressed in multiple ways:
Volume measurement: Normal adult testicular volume is greater than 14 mL in Japanese populations and greater than 17 mL in American populations, with volumes below 12 mL universally considered small or atrophic 3, 1
Linear dimensions: The length range of 3.5-5 cm aligns with normal adult testicular volumes, as testicular volume correlates directly with linear measurements 4, 5
Vietnamese population data: Mean testicular volume in healthy fathers was 13.64 ± 3.44 mL (left: 13.94 mL; right: 13.34 mL), with the left testis typically slightly larger 6
Clinical Significance of Small Testes
Testicular volumes below 12 mL are pathologically significant and require evaluation:
Risk of germ cell neoplasia: Patients with testicular volume <12 mL and age <30-40 years have a >34% risk of intratubular germ cell neoplasia (GCNIS) in the contralateral testis 7, 1
Fertility implications: Small testicular size strongly correlates with reduced total sperm count and sperm concentration, indicating impaired spermatogenesis 1, 2
Hypogonadism: Hypogonadal men and unexplained infertile men have significantly smaller testicular sizes compared to healthy fathers 6
Measurement Methods
The Prader orchidometer is the preferred clinical tool for rapid assessment, though it tends to overestimate volume:
Orchidometer measurements are easier to perform and more cost-effective than ultrasound in routine clinical practice 1
External measurements with calipers overestimate testicular dimensions by approximately 5.7 mm in length, 2.9 mm in thickness, and 1.4 mm in width compared to ultrasound, primarily due to inclusion of scrotal skin and epididymis 4, 5
Ultrasound is the gold standard for accurate volume determination but should be reserved for specific indications 1, 2
When to Perform Ultrasound
Do not routinely perform scrotal ultrasound for normal-sized testes. Reserve ultrasound for specific scenarios:
- Large hydrocele 1, 2
- Inguinal testis location 1, 2
- Epididymal enlargement/fibrosis or thickened scrotal skin 1
- Small testis with large epididymis 1
- Suspected testicular mass 2
Common Pitfall
Avoid hunting for subclinical varicoceles with ultrasound, as only palpable varicoceles benefit from treatment—non-palpable varicoceles do not improve semen parameters or fertility rates 7, 2
Risk Factors for Small Testes
- History of cryptorchidism (undescended testicles) significantly increases risk of testicular atrophy 1, 8
- Prior chemotherapy or radiation: Cranial and testicular irradiation, and cyclophosphamide therapy cause testicular atrophy and impaired spermatogenesis 9
- Hypogonadism: Testicular size negatively correlates with FSH and LH levels, and positively correlates with testosterone 6