What are the different types of uterine fibroids?

Uterine Fibroids Classification

Uterine fibroids are classified into three main anatomic types based on their location within the uterus: submucosal (SM), intramural (IM), and subserosal (SS), with this classification being critical for determining treatment approach and reproductive outcomes. 1

Primary Classification System

Submucosal Fibroids

• Located beneath the endometrium and protrude into the uterine cavity, causing distortion of the endometrial cavity 1
• Have the most severe impact on fertility, with pregnancy rates of only 10% and implantation rates of 4.3% in assisted reproduction 1
• Associated with highest risk of spontaneous abortion, preterm delivery, abnormal labor presentation, birth canal obstruction, postpartum hemorrhage, and puerperal sepsis 1
• Diagnosed with 90% sensitivity and 98% specificity using transvaginal ultrasound 1
• May be amenable to hysteroscopic resection if intracavitary 2

Intramural Fibroids

• Located within the muscular wall of the uterus (myometrium) without significant protrusion toward the cavity or serosal surface 1
• Significantly reduce pregnancy rates (16.4%) and implantation rates (6.4%) compared to women without fibroids, even when cavity distortion is absent 1
• Amenable to uterine fibroid embolization (UFE) when they contact the endometrium, though may be expelled following successful UFE in 2.2% to 7.7% of cases 2

Subserosal Fibroids

• Located on the external surface of the uterus beneath the peritoneal serosa 1
• Do not significantly affect fertility, with pregnancy rates (34.1%) and implantation rates (15.1%) similar to women without fibroids (30.1% and 15.7% respectively) 1
• Large subserosal or pedunculated fibroids may be better visualized with transabdominal ultrasound due to limited field-of-view on transvaginal approach 2
• The "bridging vessel sign" (interface vessels between uterus and juxtauterine masses) on color Doppler helps differentiate subserosal fibroids from extrauterine tumors 2

Degenerative Subtypes

MRI signal intensity and contrast enhancement patterns allow characterization of fibroids as classic, degenerated, cellular, or atypical 2

Degenerated fibroids include:

• Hyaline degeneration 2
• Carneous (red) degeneration 2
• Hydropic degeneration 2
• Fatty degeneration 2
• Cystic degeneration 2
• Myxoid degeneration 2

Diagnostic Imaging Approach

First-Line Imaging

• Combined transabdominal and transvaginal ultrasound is the most useful initial modality for evaluating suspected uterine fibroids 2, 1
• Transvaginal ultrasound achieves 90-99% sensitivity for detecting fibroids overall and 90% sensitivity with 98% specificity for submucosal fibroids specifically 2, 1
• 3D ultrasound with Doppler demonstrates 93% sensitivity and 96% specificity for differentiating fibroids from adenomyosis 2, 1

Advanced Imaging

• MRI is superior to ultrasound for identifying and mapping fibroids, altering management in up to 28% of patients 2, 1, 3
• Gadolinium-based contrast is preferred when MRI is clinically indicated for assessing fibroid vascularity and other characteristics 2
• MRI provides crucial information on location, volume, number, T1/T2 signal intensity, and enhancement patterns 2
• Post-contrast imaging allows assessment of fibroid viability, uterine artery anatomy, and ovarian arterial collateral supply 2

Color Doppler Characteristics

• Fibroids show increased peripheral vascular flow on color Doppler imaging 2
• High velocity, low resistive index (<0.7), and low pulsatility index (<1.2) in uterine arteries distinguish fibroids from adenomyosis with 93.4% sensitivity and 95.6% specificity 2

Critical Clinical Considerations

Submucosal and intramural fibroids require consideration of surgical or medical treatment before pursuing assisted reproductive technologies 1

• Non-viable or autoinfarcted fibroids occur in up to 20% of UFE candidates and do not respond to embolization, making pretreatment identification essential 2, 1
• Cervical fibroids may not respond as well or have durable response to embolization 2
• CT has limited utility for initial fibroid evaluation but can better delineate calcified fibroids that may have treatment implications 2
• Conventional MRI cannot reliably differentiate fibroids from sarcomas; diffusion-weighted imaging with ADC values incorporated into an MRI algorithm achieves 83-88% sensitivity and 97-100% specificity for this distinction 2