The size of the testes can be a source of concern, as changes may signal underlying health issues. While natural variation exists among individuals, a significant reduction in volume, medically termed testicular atrophy, warrants attention. This atrophy impacts both reproductive and hormonal health. Understanding the objective measures of size, normal functions, and specific causes provides context for determining when a consultation with a healthcare provider is appropriate.
Understanding Normal Testicular Volume
The standard measurement for testes is volume, typically expressed in milliliters (mL) or cubic centimeters (cc). For a healthy adult, the normal range for a single testis is 12 to 25 mL, with an average volume around 18 mL. One testis may be slightly larger than the other.
Clinicians use two main methods to determine this volume: the Prader orchidometer and ultrasound imaging. The orchidometer is a series of beads of known sizes used for quick estimation. Ultrasound provides a more precise calculation by measuring the length, width, and depth of the organ. A volume consistently below the 12 mL threshold is considered small or atrophic, a condition also referred to as testicular hypotrophy.
Essential Functions of the Testes
The testes are paired organs that perform two distinct and interconnected biological roles. The first is spermatogenesis, the production of sperm cells, which occurs within the seminiferous tubules. These tubules make up the majority of the testicular volume.
The second function is the synthesis and secretion of androgens, primarily the hormone testosterone. Specialized Leydig cells, located between the seminiferous tubules, produce this hormone. Testosterone regulates libido, muscle mass, bone density, and the development of secondary sexual characteristics.
Testicular volume correlates directly with the capacity for sperm production. Smaller testes often contain fewer seminiferous tubules and thus produce fewer sperm. A reduction in size frequently indicates a loss of these functional cells, which can impair fertility and lead to hormonal imbalance.
Primary Causes of Testicular Atrophy
Testicular atrophy occurs when there is damage or suppression of the cells responsible for size and function.
Exogenous Hormones
One common cause is the use of exogenous hormones, such as anabolic-androgenic steroids or testosterone replacement therapy. These external hormones signal the brain to stop producing Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH), which are needed to stimulate the testes. Without this stimulation, the testes become inactive and shrink because their natural function is suppressed.
Infections
Infections can also cause atrophy, most notably orchitis, which is inflammation of the testis. Viral orchitis is frequently linked to the mumps virus, causing swelling followed by permanent shrinkage and damage to the sperm-producing tissue. Bacterial orchitis, often resulting from sexually transmitted infections like chlamydia or gonorrhea, can similarly lead to a reduction in size.
Vascular Issues
A significant cause is a varicocele, an enlargement of the veins within the scrotum, similar to varicose veins. This condition can lead to atrophy by impairing blood flow and increasing the temperature around the testes, which is detrimental to the tissue. Testicular torsion, a medical emergency where the spermatic cord twists and cuts off the blood supply, can also cause rapid atrophy if not treated immediately.
Chronic Conditions
Chronic conditions such as excessive alcohol use and aging can contribute to atrophy. High alcohol consumption can directly damage the testosterone-producing Leydig cells, lowering hormone levels and causing shrinkage. A gradual reduction in testicular size is a common occurrence with advancing age.
When Small Size Indicates a Health Concern
A noticeable reduction in testicular size, especially if it occurs suddenly or unilaterally, requires medical evaluation. The primary concern is the accompanying loss of function, which may present as decreased fertility or hormonal deficiency. Difficulty conceiving after a year of trying strongly indicates that testicular function may be impaired.
Other symptoms warranting an immediate visit include chronic pain or a feeling of heaviness in the scrotum, which can be linked to a varicocele. Signs of low testosterone, such as reduced libido, unexplained fatigue, loss of muscle mass, or mood changes, should also prompt an evaluation. If atrophy is present, a doctor will perform a physical examination and blood tests to measure hormone levels like testosterone and FSH. Imaging, such as ultrasound, may be used to accurately measure volume and check for structural issues.