Is a 20-30% size difference between testicles (testes) a cause for concern?

Is a 20-30% Size Difference Between Testicles Normal?

A 20-30% size difference between testicles is common and generally not concerning in healthy individuals, though it warrants careful evaluation in specific clinical contexts, particularly when associated with varicocele, infertility concerns, or progressive testicular atrophy. 1

Normal Testicular Asymmetry in Healthy Populations

• Testicular asymmetry is physiologically normal: In a study of 345 healthy adolescent boys without pathology, 58.84% had a smaller left testis, and approximately 20% had either a testicular volume difference >2 mL or a testicular atrophy index (TAI) >20% 2

• The left testis is commonly smaller: This asymmetry is particularly evident during puberty (Tanner stages 3), where the difference becomes statistically significant 2

• No intervention is needed for isolated asymmetry: In healthy individuals without other clinical findings, this size difference represents normal anatomical variation 2

When Size Differences Become Clinically Significant

Varicocele-Associated Atrophy

• A persistent size difference >20% (or >2 mL) confirmed on two visits 6 months apart in the presence of a palpable varicocele strongly indicates the need for surgical intervention 1

• Surgery is particularly recommended when: There is a clinical varicocele AND abnormal semen parameters AND the patient is attempting conception 1

• Varicocele affects 35-40% of infertile men (compared to 15% of the general population), and associated testicular atrophy significantly increases infertility risk through multiple mechanisms including elevated scrotal temperature, hypoxia, and DNA damage 1

Small Testicular Volume Threshold

• Testicular volumes <12 mL are considered small or atrophic and warrant further investigation, particularly when bilateral or associated with infertility 3

• **Small testes (<12 mL) correlate with**: Impaired spermatogenesis, higher risk of intratubular germ cell neoplasia (>34% risk in contralateral testis in cancer patients), and potential hormonal dysfunction 3

• Mean testicular size strongly correlates with: Total sperm count, sperm concentration, FSH levels, and overall testicular function 4

Clinical Evaluation Approach

Physical Examination

• Use a Prader orchidometer for routine volume assessment: This is cost-effective and provides adequate accuracy for clinical decision-making 5

• Document testicular consistency and position at each well-child visit, as acquired cryptorchidism (testicular ascent) can occur and peaks around age 8 years 5

When to Order Ultrasound

Scrotal ultrasound is indicated for 5:

• Large hydrocele obscuring palpation
• Inguinal or undescended testis
• Epididymal enlargement or fibrosis
• Thickened scrotal skin
• Small testis with disproportionately large epididymis
• Assessment for testicular microcalcifications (18-fold higher cancer prevalence) 5

Hormonal Assessment

• Measure testosterone, FSH, and LH in men with small testes or significant asymmetry, as male infertility is frequently linked to hypogonadism with long-term cardiometabolic implications 5

• FSH levels negatively correlate with spermatogonia number, though they don't reliably predict sperm retrieval success in azoospermic patients 5

Critical Pitfalls to Avoid

• Do not assume all size differences require surgery: Only those with abnormal semen parameters, documented progressive atrophy, or palpable varicocele benefit from intervention 1

• Do not treat subclinical varicocele based solely on ultrasound findings: This does not improve outcomes 1

• Do not overlook serial measurements: A single measurement showing asymmetry is insufficient—document stability or progression over 6 months before recommending surgery 1, 2

• Do not ignore the contralateral testis in unilateral cryptorchidism: The descended testis may also have structural abnormalities affecting fertility 5

Cancer Risk Considerations

• Infertile men have nearly 2-fold higher risk of testicular cancer (pooled OR 1.91,95% CI 1.52-2.42), with oligozoospermic men having an 11.9-fold higher hazard ratio 5

• If testicular microcalcifications are detected on ultrasound along with atrophic testes, the patient falls into a higher-risk category that may warrant testicular biopsy discussion 1

• Men with cryptorchidism history have 3.6-7.4 times higher risk of germ cell tumors, and should perform monthly self-examinations after puberty 5