What is the appearance of a hydrocele on ultrasound?

Ultrasound Appearance of Hydrocele

A hydrocele appears on ultrasound as an anechoic (echo-free) fluid collection between the parietal and visceral layers of the tunica vaginalis surrounding the testis. 1, 2

Classic Sonographic Features

Simple hydroceles demonstrate the following characteristics:

• Anechoic fluid collection that completely or partially surrounds the testis, appearing black on grayscale imaging 1, 2
• Smooth, thin walls with clear visualization of the underlying testicular parenchyma 3
• No internal echoes or septations in uncomplicated cases 4
• Enhanced through-transmission of the ultrasound beam, making structures deep to the fluid appear brighter 4

Technical Scanning Approach

The American College of Radiology recommends a systematic examination protocol: 1

• Use a high-frequency linear transducer (7.5-15 MHz) for optimal resolution of scrotal structures 1
• Position the patient supine with the scrotum supported, scanning in both transverse and longitudinal planes through the entire scrotum 1
• Include both grayscale and color Doppler assessment to evaluate testicular blood flow and adjacent structures 1
• Scan the entire testicle in multiple planes to ensure no underlying pathology is obscured by the fluid 1

Complex Hydroceles and Warning Signs

Not all fluid collections are simple hydroceles, and certain features demand heightened scrutiny:

• Septations, debris, or internal echoes suggest a complex hydrocele, which may indicate underlying inflammation, infection, hemorrhage, or rarely, malignancy 5, 4
• Thickened or irregular walls of the tunica vaginalis raise concern for reactive processes or tumor 5
• Inability to fully visualize the testis due to large hydrocele volume is a critical pitfall—the entire testicular parenchyma must be examined to exclude underlying tumors 1, 6

Critical Clinical Pitfalls

The American College of Radiology specifically warns against several diagnostic errors: 1

• Failure to adequately visualize the entire testicle when obscured by large hydrocele, which may miss underlying testicular tumors 1, 6
• Assuming all complex-appearing fluid is benign hydrocele without evaluating for underlying causes—complex hydroceles in young men have been reported as the presenting feature of testicular tumors, including mixed germ cell tumors 5
• Inadequate assessment of both testicles for comparison, which is essential for detecting subtle abnormalities 1
• Not evaluating for causes of reactive hydrocele, such as epididymitis, orchitis, testicular torsion, or tumor 1, 7

Color Doppler Assessment

Color Doppler evaluation is essential and should demonstrate: 1

• Normal testicular blood flow within the affected testicle to exclude torsion 1
• Increased blood flow in adjacent structures (epididymis) if the hydrocele is reactive to inflammation 7
• Absence of flow within the fluid collection itself, confirming its avascular nature 4

Reactive Hydroceles

Reactive hydroceles develop secondary to underlying pathology and appear as: 7

• Anechoic fluid collections surrounding the testis, often with increased blood flow in the adjacent epididymis on Doppler imaging 7
• Associated findings may include scrotal wall thickening, epididymal enlargement, or testicular heterogeneity depending on the underlying cause 7
• Most reactive hydroceles are self-limiting and resolve with treatment of the underlying inflammatory condition 7

Follow-Up Considerations

The American College of Radiology recommends: 1

• Follow-up ultrasound may be necessary if the hydrocele persists despite treatment of the underlying condition 1
• Any complex hydrocele in a young male warrants careful evaluation and possibly short-interval follow-up or surgical exploration to exclude malignancy 5