Do I have testicular atrophy given a decrease in testicular size from 4.1cm and 4.0cm to 3.1cm and 3.4cm over a 6-week period, with a normal sperm count (60 million per milliliter) and a follicle-stimulating hormone (FSH) level of 10, which is within the normal range of 1-12.4?

Measurement Error is the Most Likely Explanation

The dramatic decrease in testicular size from 4.1cm/4.0cm to 3.1cm/3.4cm over just 6 weeks is almost certainly due to ultrasound measurement error rather than true testicular atrophy, especially given your normal sperm count of 60 million/mL and FSH of 10 IU/L. 1

Why This is Likely Measurement Error

Technical factors in ultrasound measurement:

• Incorrect caliper placement during ultrasound commonly leads to measurement errors of 20-30%, particularly with width measurements 1
• True biological change in testicular size over 4-6 weeks is extremely unlikely in adults unless acute pathology (trauma, torsion, infection) is present 1
• The measurements you describe would calculate to volumes of approximately 15-18mL initially, then dropping to 6-8mL—this represents severe atrophy that would be inconsistent with your normal sperm production 1

Your clinical picture argues against true atrophy:

• A sperm count of 60 million/mL significantly exceeds the WHO lower reference limit of 16 million/mL, confirming normal sperm production 1, 2
• FSH of 10 IU/L, while borderline-elevated, does not indicate severe testicular failure—men with true severe atrophy typically have FSH >15-20 IU/L 1, 3
• Testicular volumes <12mL are definitively considered atrophic and strongly associated with impaired spermatogenesis, yet your sperm count is normal 1

What You Should Do Next

Request a repeat scrotal ultrasound with specific instructions:

• High-frequency probes (>10 MHz) should be used to maximize resolution 1
• Measurements should include three perpendicular dimensions (length, width, height) on axial slices 1
• The same sonographer should perform the measurement if possible, or the current operator should remeasure the previous scans to minimize inter-scan variability 1
• Calculate volume using the Lambert formula: Length × Width × Height × 0.71 (not the 0.52 ellipsoid formula, which underestimates by 20-30%) 1

Understanding Your FSH Level

Your FSH of 10 IU/L warrants attention but is not alarming:

• FSH >7.6 IU/L is associated with a 5-13 fold higher risk of abnormal sperm concentration compared to FSH <2.8 IU/L, but this refers to risk of reduced counts, not absence of sperm 4
• FSH levels between 7.6-12 IU/L typically indicate mild testicular dysfunction with reduced testicular reserve, but normal sperm production remains possible 1, 3
• Up to 50% of men with non-obstructive azoospermia and elevated FSH still have retrievable sperm, so your FSH level with normal sperm count is entirely consistent 1, 3

Complete your hormonal evaluation:

• Measure LH and total testosterone to distinguish primary testicular dysfunction from secondary causes 1, 2
• Check thyroid function (TSH, free T4), as thyroid disorders commonly affect reproductive hormones and can elevate FSH 1
• Consider measuring SHBG to calculate free testosterone, as the pattern of gonadotropins helps characterize the hypothalamic-pituitary-testicular axis 1

Do You Have Testicular Atrophy?

Based on your normal sperm count, the answer is almost certainly no. True testicular atrophy with volumes of 6-8mL (as the second ultrasound would suggest) is incompatible with a sperm count of 60 million/mL 1, 5. The strong correlation between testicular volume and sperm production means that severe atrophy would manifest as severe oligospermia or azoospermia, not normal counts 5.

Important Monitoring and Protective Actions

Given your borderline FSH, take these steps:

• Repeat semen analysis in 3-6 months to establish whether parameters are stable or declining, as single analyses can be misleading 1
• Never use exogenous testosterone or anabolic steroids, as these completely suppress spermatogenesis through negative feedback and can cause azoospermia that takes months to years to recover 1, 3
• Consider sperm cryopreservation (banking 2-3 ejaculates) if follow-up shows declining sperm concentration, especially if approaching 20 million/mL 1
• Optimize modifiable factors: smoking cessation, maintain healthy body weight (BMI <25), minimize heat exposure to testes 1, 6

When to Seek Specialist Evaluation

Refer to male reproductive specialist if:

• Repeat ultrasound confirms testicular volume <12mL bilaterally 1
• Follow-up semen analysis shows sperm concentration declining below 20 million/mL 1
• You develop a palpable testicular mass 1
• You have a history of cryptorchidism (undescended testicles), which increases risk of intratubular germ cell neoplasia to >34% with volumes <12mL 7, 1