How do you differentiate uterine fibroids from uterine AVMs?

Distinguishing Uterine Fibroids from Uterine AVMs

The key distinction between uterine fibroids and uterine AVMs lies in their Doppler flow patterns: fibroids demonstrate peripheral rim vascularity with high-resistance flow (RI >0.7, PI >1.2), while AVMs show chaotic, turbulent flow with low-resistance patterns throughout the lesion. 1

Initial Diagnostic Approach

Begin with transvaginal ultrasound (TVUS) combined with transabdominal ultrasound (TAUS) and color Doppler as the first-line diagnostic modality, which has 90-99% sensitivity for detecting fibroids. 2, 1

Gray-Scale Ultrasound Features

Fibroids:

• Well-defined, solid mass with variable echogenicity depending on degeneration type 1
• Typically homogeneous or heterogeneous internal architecture 2
• May show posterior acoustic shadowing if calcified 2

AVMs:

• Multiple anechoic or hypoechoic tubular structures representing dilated vessels 1
• Lack of discrete solid mass formation 1

Critical Doppler Characteristics (The Definitive Differentiator)

Fibroids:

• Peripheral rim vascularity with vessels arranged around the mass periphery 2, 1
• High-resistance flow patterns: RI >0.7 and PI >1.2 2, 1
• Peak systolic velocity typically <64 cm/s in feeding uterine arteries 1
• Organized vascular pattern following normal arterial-capillary-venous sequence 1
• The "bridging vessel sign" (interface vessels between uterus and mass) helps differentiate subserosal fibroids from extrauterine tumors 2

AVMs:

• Chaotic, turbulent flow with multiple tangled vessels throughout the entire lesion 1
• Low-resistance, high-velocity flow patterns 1
• Arteriovenous shunting without normal capillary bed 1
• Pulsatile venous flow due to direct arteriovenous connections 1

Common Pitfall to Avoid

Hypervascular fibroids can be mistaken for AVMs due to increased vascularity, but the resistance indices remain the key differentiator—fibroids maintain high-resistance flow patterns (RI >0.7) despite increased vascularity, while AVMs demonstrate persistently low-resistance flow. 1

When to Proceed to MRI

Use MRI with gadolinium-based contrast when ultrasound findings are equivocal or detailed characterization is needed, as it may alter management in up to 28% of patients. 2, 1

MRI Characteristics

Fibroids:

• Well-circumscribed, low signal intensity masses on T2-weighted imaging 1
• Variable signal intensity depending on degeneration type (hyaline, carneous, hydropic, fatty, cystic, myxoid) 2
• Homogeneous or heterogeneous enhancement on post-contrast imaging 1
• Peripheral enhancement pattern corresponding to peripheral vascularity 2

AVMs:

• Multiple serpentine flow voids on T2-weighted imaging representing dilated vessels 1
• Intense enhancement of vascular channels on post-contrast imaging 1
• Absence of discrete solid mass 1

Diagnostic Algorithm

1. Clinical history assessment: Look specifically for abnormal uterine bleeding patterns, prior uterine instrumentation (D&C, cesarean section), or pregnancy complications that predispose to AVMs 1

2. Gray-scale ultrasound (TVUS + TAUS): Identify whether there is a discrete solid mass (fibroid) versus tangled vascular channels (AVM) 2, 1

3. Color and spectral Doppler (mandatory): Measure resistance indices and assess flow patterns—this is the critical step that definitively distinguishes the two entities 1

4. MRI if Doppler is inconclusive: Provides superior anatomic detail and confirms vascular architecture 2, 1

Clinical Context Matters

AVMs are more likely in patients with history of gestational trophoblastic disease, prior uterine surgery, or recent pregnancy, while fibroids are more common in women of reproductive age without these specific risk factors. 1