Sonographic Differentiation: Endometrioma vs Ovarian Fibroma
Endometriomas characteristically demonstrate homogeneous low-level "ground glass" echoes with posterior acoustic enhancement and absent internal vascularity, while fibromas appear as hypoechoic solid masses with acoustic attenuation (stripy shadows) and minimal to moderate blood flow. 1
Endometrioma Sonographic Features
The O-RADS US consensus guideline provides definitive imaging characteristics 1:
Classic Appearance
- Homogeneous low-level or "ground glass" internal echoes - this is the most specific feature
- Posterior acoustic enhancement (not shadowing)
- No internal vascularity on Doppler imaging - this is critical for diagnosis
- Visible surrounding ovarian parenchyma
- Unilocular or multilocular configuration
Age-Related Variations
Important caveat: In older premenopausal women, endometriomas lose their classic appearance 2:
- Multilocular cysts become more common (OR 0.70 per 10-year age decrease)
- Ground glass echogenicity becomes less common (OR 0.74 per 10-year age decrease)
- Solid components and papillations appear more frequently (OR 1.65 for papillations with increasing age)
- These atypical features can mimic malignancy, particularly when associated with high vascularity 3, 4
Additional Features
- Peripheral punctate echogenic foci may be present (occasionally with twinkling artifact on Doppler, but without posterior shadowing) 1
- In multiloculated endometriomas, flow may be observed in intervening septa only 1
Ovarian Fibroma Sonographic Features
Based on the largest dedicated fibroma study 5:
Classic Appearance
- Hypoechoic solid mass - well-demarcated, round, oval, or slightly lobulated
- Acoustic attenuation with "stripy shadows" - this is the hallmark feature (present in 44% of cases)
- Minimal to moderate vascularity on color Doppler (75% show minimal/moderate flow; only 32.79% show any flow)
- Regular or slightly irregular internal echogenicity
Size Patterns
- 70% of solid hypoechoic fibromas are <5 cm in diameter 5
- Larger fibromas (>5 cm) more commonly show mixed echogenicity with calcification, hemorrhage, or cystic spaces (70.59% of mixed lesions are >5 cm) 5
Associated Findings
- Ascites in 33% of cases - can mimic malignancy 5, 6
- Fluid in pouch of Douglas in 50% 5
- Meigs syndrome (rare, 1.6%) 5
- CA-125 elevation in 21% of cases (correlates with tumor size) 5, 6
Key Discriminating Features
| Feature | Endometrioma | Fibroma |
|---|---|---|
| Echogenicity | Homogeneous low-level/ground glass | Hypoechoic solid |
| Acoustic properties | Posterior enhancement | Acoustic attenuation/stripy shadows |
| Vascularity | Absent (except in septa) | Minimal to moderate |
| Texture | Cystic/fluid-filled | Solid |
| Size correlation | Variable | <5 cm typically solid; >5 cm often mixed |
Critical Pitfalls to Avoid
Atypical endometriomas in older premenopausal women (>40 years) may show solid components and papillations that mimic malignancy 2, 3. Pattern recognition by experienced sonographers improves accuracy from 64% to 90% 3.
Fibromas with ascites and elevated CA-125 can be mistaken for malignancy 5, 6. The presence of acoustic attenuation with stripy shadows and minimal vascularity favors benign fibroma.
Loss of ground glass echogenicity in endometriomas with solid components >1.37 cm, cyst size >11.55 cm, and age >47.5 years are independent risk factors for malignant transformation to clear cell carcinoma 4.
Pedunculated or broad ligament fibroids can mimic solid adnexal masses; look for bridging vessels to identify uterine origin 7.
Clinical Context
- Endometriomas: Typically occur in reproductive-age women (mean age 39 years with atypical features 4), often asymptomatic or associated with endometriosis symptoms
- Fibromas: Mean age 54 years, 64% postmenopausal, 64% asymptomatic 5, 6
When ultrasound features are equivocal or atypical, consultation with a US specialist or MRI characterization is recommended per O-RADS guidelines 1, 7.