What could cause a decrease in testicle size?

Testicular Shrinkage: Causes and Evaluation

Testicular shrinkage (atrophy) most commonly results from hormonal suppression, prior testicular injury, varicocele, cryptorchidism history, genetic conditions like Klinefelter syndrome, or chronic medical conditions—and you need urgent evaluation with physical examination, hormonal testing (FSH, LH, testosterone), and scrotal ultrasound to determine the cause and preserve fertility potential. 1, 2

Most Common Causes of Testicular Atrophy

Hormonal Suppression

• Exogenous testosterone use is the most reversible cause of testicular shrinkage in adults. Testosterone therapy provides negative feedback to the hypothalamus and pituitary, suppressing LH and FSH secretion, which eliminates intratesticular testosterone production and causes the testicles to shrink by 16-23% within 4-16 weeks. 3, 4
• Anabolic steroid use has identical effects to testosterone therapy, causing rapid testicular atrophy that may take months to years to reverse after cessation. 3
• Recovery of testicular size and sperm production occurs in most men after stopping testosterone, but the timeline is unpredictable and can extend beyond 12 months in some cases. 3, 4

Prior Testicular Injury or Infection

• Mumps orchitis, testicular torsion, and trauma are painful events that cause permanent testicular atrophy with heterogeneous echogenicity on ultrasound. 5, 6
• These conditions result in irreversible damage to the seminiferous tubules where sperm production occurs. 5, 6

Varicocele

• Varicoceles cause progressive bilateral testicular atrophy over time, even though the varicocele is typically unilateral (left-sided). 7
• Men with varicoceles have significantly smaller testicles bilaterally compared to men without varicoceles, even when sperm density is similar. 7
• The atrophic process is progressive, making early surgical correction important to prevent further testicular damage. 7

Cryptorchidism History

• Undescended testicles that required surgical correction (orchidopexy) often remain smaller than normal due to prenatal testicular damage or surgical injury to blood vessels. 5
• Even the contralateral descended testicle may be smaller than normal in men with a history of unilateral cryptorchidism. 2, 8
• Cryptorchid testicles have markedly elevated rates of infertility and a modestly increased cancer risk. 5

Genetic Conditions

• Klinefelter syndrome (47,XXY) is the most common genetic cause of small testicles, presenting with a spectrum from severe hypogonadism to near-normal virilization but with infertility. 5, 6
• On ultrasound, Klinefelter patients show small hyperechoic or hypoechoic nodules with homogeneous echogenicity in the remaining testicular tissue. 6
• These men have elevated breast cancer risk approaching female rates. 5

Chronic Medical Conditions

• Liver cirrhosis, chronic alcoholism, hemochromatosis, and Curschmann-Steinert myotonic dystrophy all cause testicular atrophy as a consequence of systemic disease. 5
• Chemotherapy, immunosuppressive drugs, and radiation therapy cause dose-dependent testicular damage. 5

Critical Diagnostic Evaluation

Physical Examination Findings

• Measure testicular volume using a Prader orchidometer—volumes below 12 mL indicate atrophy and warrant further investigation. 2, 8
• A testicular length of 4 cm corresponds to approximately 15-18 mL volume, which is at the lower limit of normal. 8
• Assess for varicocele, which feels like a "bag of worms" in the scrotum and is more prominent when standing. 7
• Check for size discrepancy between testicles—differences greater than 2 mL or 20% require ultrasound evaluation. 8

Hormonal Testing

• Elevated FSH (>7.6 IU/L) with testicular atrophy strongly indicates spermatogenic failure and primary testicular dysfunction. 1, 2
• Measure FSH, LH, and total testosterone simultaneously to distinguish primary testicular failure (high FSH/LH, low testosterone) from secondary hypogonadism (low FSH/LH, low testosterone). 3, 1
• If FSH is elevated above 7.6 IU/L with small testicles, the likelihood of normal sperm production is significantly reduced. 1, 2

Genetic Testing Indications

• Obtain karyotype analysis if FSH is elevated and testicles are atrophic to exclude Klinefelter syndrome and other chromosomal abnormalities. 1, 2
• Y-chromosome microdeletion testing (AZFa, AZFb, AZFc regions) is mandatory if sperm concentration is below 5 million/mL. 1
• Complete AZFa and AZFb deletions have almost zero likelihood of successful sperm retrieval. 1

Imaging

• Scrotal ultrasound is indicated when physical examination is difficult or when there is significant size discrepancy between testicles. 2, 8
• Ultrasound helps differentiate causes: heterogeneous echogenicity suggests torsion, trauma, or orchitis; homogeneous hypoechogenicity suggests cryptorchidism or hernia; isoechoic appearance suggests varicocele. 6

Fertility Implications and Urgent Actions

Sperm Production Assessment

• Testicular atrophy with FSH >7.6 IU/L is strongly associated with absent or severely reduced sperm production. 1, 2
• Mean testicular size correlates most strongly with total sperm count and sperm concentration—testicles smaller than 14 mL show impaired sperm quantity and quality. 9
• However, up to 50% of men with non-obstructive azoospermia and elevated FSH still have retrievable sperm with microsurgical testicular sperm extraction (micro-TESE). 1

Immediate Fertility Preservation

• If you desire future fertility, obtain semen analysis immediately and consider sperm cryopreservation before testicular function deteriorates further. 1
• Micro-TESE is 1.5 times more successful than conventional testicular sperm extraction and should be performed by experienced specialists. 1, 2

Critical Medication Warning

• Never use exogenous testosterone if you want to preserve fertility—it will completely suppress sperm production and may cause irreversible azoospermia. 3, 1
• If you are currently using testosterone or anabolic steroids, stop immediately and seek fertility evaluation. 3, 4

Cancer Surveillance

• Atrophic testicles (<12 mL) carry increased risk of testicular cancer and require regular self-examination. 2
• Men with testicular atrophy and testicular microcalcification on ultrasound should undergo testicular biopsy due to elevated risk of germ cell tumors. 2
• Cryptorchid testicles have increased cancer risk even after surgical correction. 5

Treatment Options Based on Cause

If Testosterone-Induced

• Discontinue testosterone immediately—testicular size typically recovers within 4-12 weeks after cessation, though sperm production may take longer. 4
• Consider hCG injections (500-2500 IU, 2-3 times weekly) to stimulate intratesticular testosterone production and accelerate recovery of spermatogenesis. 3, 10

If Varicocele-Related

• Surgical varicocele repair prevents progressive testicular atrophy and may improve fertility potential, especially if performed early. 7

If Primary Testicular Failure

• Micro-TESE offers 40-60% sperm retrieval rates even with elevated FSH and atrophic testicles. 1, 2
• Assisted reproductive technology (IVF/ICSI) provides the highest pregnancy rates when sperm are retrieved. 3, 1

The key message: testicular shrinkage is never normal and demands immediate evaluation to identify reversible causes, preserve fertility, and screen for malignancy.