How to differentiate uterine fibroid from uterine Arteriovenous Malformation (AVM)?

Distinguishing Uterine Fibroid from Uterine AVM

Begin with transvaginal ultrasound combined with color and spectral Doppler imaging, which is the first-line diagnostic approach—fibroids show peripheral rim vascularity with high-resistance flow (RI >0.7), while AVMs demonstrate chaotic, turbulent flow with low-resistance patterns throughout the lesion. 1

Initial Diagnostic Approach

Start with combined ultrasound evaluation:

• Perform both transvaginal ultrasound (TVUS) and transabdominal ultrasound (TAUS) together, as this combination is the most useful initial modality with 90-99% sensitivity for detecting fibroids 2, 1
• Color Doppler is mandatory—not optional—for evaluating any uterine mass in patients with abnormal bleeding 1
• TVUS provides superior contrast and spatial resolution for detailed characterization 2

Key Ultrasound Differentiating Features

Gray-Scale Characteristics

• Fibroids: Well-defined, solid mass with variable echogenicity and clear borders 1
• AVMs: May appear as complex vascular spaces or heterogeneous masses, often with history of recent pregnancy, miscarriage, or curettage 3, 4, 5

Critical Doppler Findings (The Decisive Factor)

Vascular Pattern:

• Fibroids: Peripheral rim vascularity with organized arterial-capillary-venous sequence 1
• AVMs: Chaotic, turbulent flow with multiple tangled vessels distributed throughout the entire lesion 1, 3, 4

Spectral Doppler Parameters:

• Fibroids: High-resistance flow with resistive index (RI) >0.7 and pulsatility index >1.2, even in hypervascular fibroids 2, 1
• Fibroids: Peak systolic velocity typically <64 cm/s in uterine arteries 2, 1
• AVMs: Low-resistance, high-velocity turbulent flow patterns 3, 4

This resistance index difference is the key differentiator—fibroids maintain high-resistance flow patterns despite increased vascularity, while AVMs show persistently low-resistance flow. 1

Clinical Context Clues

High suspicion for AVM when:

• Recent history of pregnancy termination, miscarriage, or curettage (8-89 days prior) 4
• Torrential vaginal bleeding not controlled by standard measures 3, 4
• Bleeding triggered or worsened by curettage 4, 5
• History of gestational trophoblastic disease 5

Fibroids more likely when:

• Chronic symptoms of abnormal uterine bleeding or pelvic pressure 6
• No recent pregnancy-related events 2

When to Proceed to MRI

Order MRI with gadolinium-based contrast when: 2, 1

• Doppler findings are equivocal or inconclusive 1
• Detailed characterization needed for surgical planning 2
• Multiple masses present making ultrasound assessment difficult 2

MRI Characteristics

Fibroids:

• Well-circumscribed, low signal intensity on T2-weighted imaging 1
• Homogeneous or heterogeneous enhancement depending on degeneration type 1
• Variable signal based on degeneration (hyaline, carneous, cystic, myxoid) 2

AVMs:

• Serpentine flow voids on T2-weighted imaging representing dilated vessels 3
• Intense enhancement of vascular channels on post-contrast sequences 3

Common Pitfalls to Avoid

• Never perform blind curettage on suspected AVM—this can trigger life-threatening hemorrhage 4, 5
• Do not rely on gray-scale ultrasound alone; Doppler assessment is essential 1
• Hypervascular fibroids can mimic AVMs on color Doppler, but spectral Doppler will show high-resistance flow in fibroids versus low-resistance in AVMs 1
• In postmenopausal women with growing "fibroid," consider leiomyosarcoma and obtain MRI with diffusion-weighted imaging 2, 6

Diagnostic Algorithm Summary

1. Clinical history: Specifically ask about recent pregnancy events, curettage, or miscarriage 4, 5
2. Gray-scale TVUS + TAUS: Assess mass characteristics and borders 1
3. Color Doppler: Evaluate vascular distribution pattern (peripheral vs. diffuse chaotic) 1
4. Spectral Doppler: Measure resistance indices—this is the decisive step (RI >0.7 = fibroid; low RI with turbulent flow = AVM) 2, 1
5. MRI with contrast: If Doppler inconclusive or detailed mapping needed 1