Expected Scrotal Ultrasound Findings in Non-Obstructive Azoospermia
In men with non-obstructive azoospermia (NOA), scrotal ultrasound typically reveals small testicular volumes (atrophic testes), normal epididymal architecture without cystic or tubular dilation, and often non-homogeneous testicular parenchyma with possible testicular microcalcifications. 1, 2
Primary Testicular Findings
Testicular Volume and Size
- Reduced testicular volume is the hallmark finding, with NOA patients showing significantly smaller testes compared to healthy controls and men with obstructive azoospermia 2
- The atrophic appearance reflects primary testicular dysfunction and spermatogenic failure 3
- This contrasts sharply with obstructive azoospermia, where testicular volumes remain normal 2
Testicular Parenchymal Architecture
- Non-homogeneous testicular architecture is commonly observed, representing signs of testicular dysgenesis and impaired spermatogenesis 1
- Testicular microcalcifications (TM) may be present, which are associated with an 18-fold higher prevalence of testicular cancer in infertile men 1
- These heterogeneous patterns reflect the underlying spermatogenic dysfunction 1
Epididymal and Ductal Findings
Normal Epididymal Appearance
- The epididymis shows no significant abnormalities in NOA patients 2
- Specifically, there is absence of cystic or tubular dilation of the epididymis, which distinguishes NOA from obstructive azoospermia 2
- The vas deferens is typically present and normal in caliber 3
This is a critical distinguishing feature: In obstructive azoospermia, cystic or tubular dilation of the epididymis is found in all patients, while NOA patients have normal epididymal architecture 2
Microvascular Characteristics
Blood Flow Parameters
- Reduced mean vascular diameter is characteristic of NOA compared to obstructive azoospermia 4
- Decreased vessel density and lower fractal number are observed 4
- Mean vascular diameter shows negative correlation with FSH levels (r = -0.214) and age (r = -0.240) 4
- These microcirculatory changes reflect the impaired spermatogenic function 4
Clinical Utility and Diagnostic Value
When to Perform Scrotal Ultrasound
The European Association of Urology guidelines specify that scrotal ultrasound has a relevant role in NOA evaluation for 1:
- Testicular volume assessment when physical examination is difficult (large hydrocele, inguinal testis, epididymal enlargement/fibrosis, thickened scrotal skin) 1
- Detection of testicular tumors, as infertile males have higher risk (pooled OR 1.91,95% CI 1.52-2.42) 1
- Assessment of testicular anatomy and structure for signs of testicular dysgenesis 1
Diagnostic Differentiation
Scrotal ultrasound effectively distinguishes NOA from obstructive azoospermia as a less invasive method 2:
- NOA: Small testes + normal epididymis + reduced vascularity 2, 4
- Obstructive azoospermia: Normal-sized testes + epididymal dilation + normal vascularity 2
Important Caveats
Incidental Findings
- Hypoechoic lesions are found in approximately 14% of men with NOA undergoing ultrasound evaluation 5
- Most lesions <5mm are benign and may be managed conservatively with serial ultrasound if tumor markers are negative 5
- Enlarging lesions or those >5mm should be considered for histological examination 5
Limitations of Ultrasound
- While ultrasound can suggest NOA based on testicular volume and architecture, FSH levels do not accurately predict the presence of spermatogenesis in all cases, as men with maturation arrest can have normal FSH and testicular volume 1
- Routine ultrasound screening for all infertile men may result in over-diagnosis of incidental testicular masses 1
- Physical examination with Prader orchidometer remains a cost-effective surrogate for volume measurement in most cases 1