What are the subtypes and clinical features of uterine fibroids?

Uterine Fibroid Subtypes and Clinical Features

Anatomic Classification System

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

Submucosal Fibroids

• Located beneath the endometrium and protrude into the uterine cavity, causing distortion of the endometrial surface 1
• Carry the most severe reproductive impact, with pregnancy rates of only 10% and implantation rates of 4.3% in assisted reproduction 1
• Associated with significantly elevated risks of spontaneous abortion, preterm delivery, abnormal fetal presentation during labor, birth canal obstruction, postpartum hemorrhage, and puerperal sepsis 1
• Can be diagnosed with transvaginal ultrasound (TVUS) with 90% sensitivity and 98% specificity 2, 1
• May be expelled following successful uterine fibroid embolization (UFE) in 2.2% to 7.7% of cases 2

Intramural Fibroids

• Located within the myometrial wall without significant protrusion toward either the endometrial cavity or serosal surface 1
• Significantly reduce pregnancy rates (16.4%) and implantation rates (6.4%) compared to women without fibroids, even when the endometrial cavity is not distorted 1
• Amenable to UFE when broad-based 2

Subserosal Fibroids

• Located on the external uterine surface beneath the peritoneal serosa 1
• Do not significantly impair fertility, with pregnancy rates (34.1%) and implantation rates (15.1%) comparable to women without fibroids (30.1% and 15.7% respectively) 1
• The "bridging vessel sign" (interface vessels between uterus and juxtauterine masses) on color Doppler helps differentiate subserosal fibroids from extrauterine tumors 2
• Pedunculated subserosal fibroids may be treated hysteroscopically, laparoscopically, or with UFE depending on stalk caliber 2

Clinical Presentation

Symptomatic Features

• Heavy or prolonged menstrual bleeding and abnormal uterine bleeding are the most common presentations 3, 4, 5
• Pelvic pressure, fullness, or pain 3, 5
• Bowel dysfunction and constipation 5
• Urinary frequency, urgency, or retention 5
• Low back pain 5
• Dyspareunia 5
• Infertility and recurrent pregnancy loss 3, 4
• Resultant anemia from chronic blood loss 4

Asymptomatic Presentation

• Many fibroids are discovered incidentally on clinical examination or imaging in asymptomatic women 5
• Asymptomatic fibroids require no intervention but should be followed to document stability in size 4

Diagnostic Imaging Characteristics

Ultrasound Features

• Combined transabdominal (TAUS) and transvaginal ultrasound (TVUS) is the most useful first-line modality for initial evaluation 2, 1
• TVUS demonstrates 90-99% sensitivity for detecting fibroids overall 2, 1
• Three-dimensional ultrasound with Doppler shows 93% sensitivity and 96% specificity for differentiating fibroids from adenomyosis 2
• 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

MRI Characteristics

• MRI is superior to ultrasound for identifying and mapping fibroids, altering management in up to 28% of patients 2, 1
• Gadolinium-based contrast is preferred when MRI is clinically indicated 2
• MRI characterizes fibroids as classic, degenerated (hyaline, carneous, hydropic, fatty, cystic, myxoid), cellular, or atypical based on signal intensity and enhancement patterns 2
• Provides crucial pretreatment information including location, volume, number, T1- and T2-weighted signal intensity, and enhancement 2
• Nonviable or autoinfarcted fibroids are found in up to 20% of UFE candidates and do not respond to embolization 2, 1

CT Characteristics

• No relevant literature supports CT as initial imaging for treatment planning 2
• CT better delineates calcified fibroids compared to ultrasound and MRI, which may have treatment implications 2

Critical Clinical Pitfalls

• Conventional MRI cannot accurately differentiate fibroids from sarcomas, a critical distinction for surgical planning 2
• Cervical fibroids may not respond well or have durable response to embolization 2
• TVUS has limited depth of penetration and shallow focal length, limiting evaluation of large or subserosal/pedunculated fibroids 2
• Submucosal and intramural fibroids require consideration of surgical or medical treatment before proceeding with assisted reproductive technologies 1