Distinguishing Uterine Fibroid from Uterine AVM
Primary Distinction
The critical distinction between a uterine fibroid and a uterine AVM is made using color Doppler ultrasound: fibroids show peripheral vascularity with high-resistance flow patterns, while AVMs demonstrate chaotic, high-velocity, low-resistance flow throughout the lesion with turbulent arteriovenous shunting.
Clinical Presentation Differences
Uterine Fibroids
- Present with chronic symptoms including menorrhagia, pelvic pressure, and pelvic pain that develop gradually 1
- May cause acute severe pelvic pain only when undergoing degeneration, accompanied by fever and leukocytosis 2
- Typically discovered incidentally or during evaluation for chronic symptoms 3
Uterine AVMs
- Present with acute, life-threatening vaginal bleeding that is often torrential and uncontrollable with standard measures 4, 5
- Bleeding episodes are frequently triggered after pregnancy loss, termination, or curettage, occurring 8-89 days post-procedure 5
- History of recent pregnancy, miscarriage, or uterine instrumentation is a critical red flag 5, 6
Ultrasound Characteristics: The Definitive Differentiator
Initial Imaging Approach
- Transvaginal ultrasound (TVUS) combined with transabdominal ultrasound (TAUS) and color Doppler is the first-line diagnostic modality 3, 2
- TVUS has 90-99% sensitivity for detecting fibroids 3
Fibroid Ultrasound Features
- Gray-scale appearance: Well-defined, solid mass with variable echogenicity (hypoechoic to hyperechoic) 3
- Color Doppler: Peripheral rim vascularity with vessels at the periphery or feeding vessels at the base 3
- Spectral Doppler: High-resistance flow with resistive index >0.7 and pulsatility index >1.2 3
- Peak systolic velocity typically <64 cm/s in uterine arteries 3
- Organized vascular pattern following normal arterial-capillary-venous sequence 3
AVM Ultrasound Features
- Gray-scale appearance: May show heterogeneous mass or appear as dilated, tortuous vascular channels within the myometrium 5, 6
- Color Doppler: Chaotic, turbulent flow with multiple tangled vessels throughout the lesion creating a "bag of worms" appearance 4, 5
- Spectral Doppler: Low-resistance, high-velocity arterial waveforms with pulsatility index <1.0 and resistive index <0.4 5
- Arteriovenous shunting with arterialized venous flow (loss of normal venous phasicity) 5, 6
- Peak systolic velocities often exceed 100 cm/s 5
MRI Characteristics When Ultrasound is Equivocal
When to Use MRI
- MRI with gadolinium-based contrast is preferred when ultrasound findings are equivocal or detailed characterization is needed 2
- MRI excels at identifying and mapping fibroids and may alter management in up to 28% of patients 3
Fibroid MRI Features
- T2-weighted imaging: Well-circumscribed, low signal intensity mass (classic fibroid) 3
- Variable signal intensity depending on degeneration type (hyaline, cystic, hemorrhagic) 3
- Post-contrast: Homogeneous or heterogeneous enhancement depending on viability 3
- Organized vascular supply from uterine arteries 3
AVM MRI Features
- T2-weighted imaging: Serpiginous flow voids representing dilated vessels 4, 6
- Absence of a discrete mass lesion 6
- Post-contrast: Intense early enhancement with rapid washout in dilated vascular channels 4
- Direct arteriovenous connections without intervening capillary bed 4, 6
Critical Diagnostic Algorithm
Step 1: Clinical History Assessment
- Recent pregnancy, miscarriage, or uterine procedure? → High suspicion for AVM 5, 6
- Chronic symptoms without recent instrumentation? → More consistent with fibroid 1
- Acute life-threatening bleeding? → AVM until proven otherwise 4, 5
Step 2: Gray-Scale Ultrasound
- Well-defined solid mass? → Proceed to Doppler evaluation for fibroid 3
- Heterogeneous area with vascular channels? → High suspicion for AVM, proceed to Doppler 5
Step 3: Color and Spectral Doppler (THE CRITICAL STEP)
- Peripheral vascularity + high-resistance flow (RI >0.7, PI >1.2)? → Fibroid confirmed 3
- Chaotic flow throughout + low-resistance flow (RI <0.4, PI <1.0) + arterialized veins? → AVM confirmed 5
Step 4: MRI if Doppler Inconclusive
- Discrete enhancing mass with organized vessels? → Fibroid 3
- Serpiginous flow voids with direct AV shunting? → AVM 4, 6
Common Pitfalls and How to Avoid Them
Pitfall 1: Failing to Obtain Doppler Imaging
- Never rely on gray-scale ultrasound alone when evaluating a uterine mass in a patient with abnormal bleeding 3, 5
- Color and spectral Doppler are mandatory components of the evaluation 3
Pitfall 2: Performing Curettage Without Doppler Evaluation
- Curettage of an AVM can trigger catastrophic hemorrhage 5, 6
- Always obtain Doppler ultrasound before any uterine instrumentation in patients with post-pregnancy bleeding 5
Pitfall 3: Misinterpreting Hypervascular Fibroids as AVMs
- Hypervascular fibroids still maintain high-resistance flow patterns (RI >0.7) despite increased vascularity 3
- AVMs demonstrate low-resistance flow (RI <0.4) with arterialized venous waveforms 5
- The resistance indices are the key differentiator 3, 5
Pitfall 4: Delaying Diagnosis in Acute Bleeding
- In a patient with torrential bleeding post-pregnancy or post-curettage, assume AVM and obtain urgent Doppler ultrasound 5
- Do not wait for hemodynamic stabilization to image—diagnosis guides immediate management 4, 5
Management Implications of Correct Diagnosis
Fibroid Management
- Options include observation, medical management, uterine fibroid embolization (UFE), myomectomy, or hysterectomy depending on symptoms and fertility goals 1
- UFE is appropriate for symptomatic fibroids with bilateral uterine artery embolization 1
AVM Management
- Uterine artery embolization is first-line treatment for symptomatic AVMs in reproductive-age women desiring fertility preservation 4, 5
- Surgical intervention (curettage, myomectomy) is contraindicated as it can cause life-threatening hemorrhage 5, 6
- Hysterectomy is reserved for failed embolization or patients not desiring fertility 5