What are the types of fibroids, their locations, and layer of origination?

Types of Uterine Fibroids and Their Layers of Origination

Uterine fibroids are classified into three main types based on their location within the uterine wall layers: submucosal, intramural, and subserosal fibroids, each with distinct clinical implications for symptoms, fertility, and treatment approaches. 1

Classification by Layer of Origination

1. Submucosal Fibroids

• Origin: Develop from myometrial cells just beneath the endometrium
• Location: Protrude into the uterine cavity
• FIGO Classification: Type 0-2
  • Type 0: Completely intracavitary
  • Type 1: <50% intramural extension
  • Type 2: ≥50% intramural extension
• Clinical Impact:
  • Highest impact on fertility with significantly reduced pregnancy rates (10%) and implantation rates (4.3%) 1
  • Most likely to cause abnormal uterine bleeding
  • Associated with increased risk of spontaneous abortion

2. Intramural Fibroids

• Origin: Develop within the myometrium (muscular wall of the uterus)
• Location: Confined within the uterine wall
• FIGO Classification: Types 3-4
  • Type 3: Contacts endometrium, 100% intramural
  • Type 4: Entirely intramural, no contact with endometrium or serosa
• Clinical Impact:
  • Moderate impact on fertility with reduced pregnancy rates (16.4%) and implantation rates (6.4%) even without cavity distortion 1
  • Can cause heavy menstrual bleeding and pelvic pressure when large
  • May be expelled following uterine fibroid embolization in 2.2-7.7% of cases when contacting the endometrium 1

3. Subserosal Fibroids

• Origin: Develop from the outer layer of the myometrium
• Location: Project outward from the uterine serosa
• FIGO Classification: Types 5-7
  • Type 5: ≥50% intramural, contacts serosa
  • Type 6: <50% intramural, mostly subserosal
  • Type 7: Attached to serosa by a stalk (pedunculated)
• Clinical Impact:
  • Minimal impact on fertility with pregnancy rates (34.1%) and implantation rates (15.1%) similar to women without fibroids 1
  • May cause pressure symptoms on adjacent organs (bladder, bowel)
  • Can be differentiated from extrauterine tumors by the "bridging vessel sign" on Doppler imaging 1

4. Other Classifications

• Cervical fibroids: Originate in the cervical tissue
• Parasitic fibroids: Detached from uterus and receive blood supply from other organs
• FIGO Type 8: Fibroids in other locations (cervical, broad ligament, parasitic)

Diagnostic Imaging for Fibroid Classification

Ultrasound Assessment

• Transvaginal ultrasound (TVUS):

  • First-line imaging with 90-99% sensitivity for detecting fibroids 1
  • Excellent for submucosal fibroids (90% sensitivity, 98% specificity) 1
  • Limited for large subserosal/pedunculated fibroids due to field-of-view constraints

• Transabdominal ultrasound (TAUS):

  • Complementary to TVUS for large fibroids or enlarged uterus 1
  • Useful when TVUS has poor acoustic penetration

• Doppler imaging:

  • Shows increased peripheral vascular flow in fibroids 1
  • Helps differentiate subserosal fibroids from extrauterine tumors via "bridging vessel sign" 1

MRI Evaluation

• Superior for fibroid mapping with potential to alter management in up to 28% of patients 1, 2
• Provides detailed information on:
  • Exact location relative to endometrium and serosa
  • Size, number, and enhancement patterns
  • Signal characteristics to identify degeneration types
• Recommended for complex cases with multiple fibroids or when planning minimally invasive procedures 2, 3

Clinical Implications by Fibroid Type

Impact on Fertility

• Submucosal fibroids: Strongest negative impact on fertility; surgical removal recommended before assisted reproductive technology 1, 4
• Intramural fibroids: Moderate impact on fertility, especially when >4 cm; removal may improve outcomes 4, 5
• Subserosal fibroids: Minimal impact on fertility; removal not necessary for fertility purposes 1, 4

Treatment Considerations

• Submucosal fibroids: Hysteroscopic resection is preferred for types 0-1 1
• Intramural fibroids: May be treated with myomectomy or uterine fibroid embolization 1
• Subserosal fibroids: Laparoscopic approach for pedunculated fibroids 1, 4

Important Clinical Pitfalls

• Failure to accurately classify fibroids may lead to inappropriate treatment selection
• Multiple imaging modalities may be needed for complete assessment of fibroid location and number
• Large fibroids (>7cm) may limit transvaginal ultrasound assessment and require MRI for accurate mapping 2
• Rapid growth of fibroids warrants investigation for potential malignancy, particularly in perimenopausal women 2

The FIGO classification system provides standardized terminology for describing fibroid locations, which is essential for treatment planning and communication between clinicians 3, 6.