Ultrasound Measurement Protocol for Epididymal Head in Adult Males
The epididymal head should be measured in two perpendicular planes using high-resolution ultrasound (≥7.5 MHz transducer), with the upper reference limit being 12 mm. 1, 2
Equipment and Technical Requirements
- Use a high-frequency linear transducer (≥7.5 MHz) for optimal resolution of scrotal structures 3, 4
- Position the patient supine with the scrotum supported on a towel between the thighs to stabilize structures 4
- Apply generous ultrasound gel to ensure adequate acoustic coupling 4
Measurement Technique for Epididymal Head
Perform measurements in two perpendicular planes (anteroposterior and transverse dimensions) at the level of the upper pole of the testis where the epididymal head is typically located 1, 5
Key Measurement Steps:
- Identify the epididymal head, which appears isoechoic relative to the testis and is located above the upper pole of the testis in 88-98% of normal cases 1
- Measure the maximum diameter in the anteroposterior plane first 1, 5
- Rotate the probe 90 degrees and measure the maximum transverse diameter 1, 5
- Normal epididymal head size is 7.6 ± 1.6 mm (mean ± SD), with the upper reference limit being 12 mm 1, 2
Anatomical Variations to Recognize
- In approximately 9-11% of cases, the epididymis may be inverted with the head located below the lower pole of the testis 1
- The epididymal body may be positioned posterior to the testis in 6-9% of cases 1
- Document any anatomical variants as they can affect interpretation and comparison with future studies 1, 4
Additional Epididymal Measurements
While evaluating the epididymal head, also measure:
- Epididymal body: normal 3.2 ± 0.8 mm (upper limit approximately 6 mm) 1, 2
- Epididymal tail: normal size with upper limit of 6 mm 2
- Epididymo-deferential loop: 7.7 ± 1.3 mm 1
Color Doppler Assessment
- Apply color Doppler to assess vascularization of the epididymal head, as blood flow is normally detectable in 100% of healthy men 6
- Normal resistive index (RI) for the epididymal head is approximately 0.54-0.55 6
- Increased vascularity may indicate inflammation, while decreased flow patterns should be documented 2, 6
Documentation Requirements
Include in your report:
- Precise measurements of epididymal head in two planes with units (mm) 1, 4
- Echogenicity relative to testis (normally isoechoic) 1, 4
- Anatomical position (superior, inferior, or variant location) 1, 4
- Presence or absence of cystic components or masses 5, 4
- Doppler flow characteristics if assessed 6, 4
- Any associated findings such as dilated efferent ductules within the testis 5
Common Pitfalls to Avoid
- Do not confuse the epididymal head with small hydroceles or fluid collections at the upper pole 4
- Avoid measuring obliquely; ensure perpendicular planes for accurate dimensions 1, 4
- Recognize that epididymal enlargement >12 mm warrants further evaluation for obstruction, inflammation, or masses 2, 4
- In patients with suspected von Hippel-Lindau disease, carefully evaluate for cystadenomas which appear as solid masses with small cystic components (15-20 mm) 5