FIGO Class 4 Myoma Definition
A FIGO Class 4 uterine leiomyoma (fibroid) is an intramural fibroid where less than 50% of the mass extends into the endometrial cavity (submucosal component), with the majority remaining within the myometrial wall. 1, 2
Understanding the FIGO Classification System
The International Federation of Gynecology and Obstetrics (FIGO) developed a standardized classification system to uniformly describe uterine fibroids based on their anatomic relationship to the endometrium, myometrium, and uterine serosa 3, 1. This classification is essential for:
- Treatment planning and surgical approach selection
- Predicting therapeutic responses
- Preventing complications
- Standardizing communication between providers
Specific Characteristics of Type 4 Fibroids
Type 4 fibroids are intramural masses with a submucosal component comprising <50% of the total fibroid volume 1, 2. Key features include:
- Primary location: Within the myometrial wall (intramural)
- Endometrial cavity involvement: Less than half of the fibroid protrudes into the uterine cavity
- Distinguishing feature: The majority of the mass (>50%) remains embedded in the myometrium
This contrasts with:
- Type 3: Intramural with ≥50% submucosal extension
- Type 5: Entirely intramural with no cavity involvement
- Types 0-2: Predominantly or entirely submucosal
Clinical Significance
Type 4 fibroids occupy a transitional position between predominantly submucosal (Types 0-3) and purely intramural (Type 5) fibroids 1, 2. Their clinical behavior and treatment approach depend on:
- The degree of endometrial cavity distortion
- Associated symptoms (abnormal uterine bleeding, bulk symptoms)
- Patient fertility goals
- Size and number of concurrent fibroids
Important caveat: While Type 4 fibroids have submucosal extension, research indicates that abnormal uterine bleeding associated with FIGO Type 4-7 leiomyomas is related to factors other than vascular density alone 4. The mechanism of bleeding is multifactorial and not solely dependent on the degree of cavity involvement.
Diagnostic Approach
Ultrasound should be the first-line imaging modality for diagnosing and classifying uterine fibroids 3, 5. However, MRI is superior for accurate FIGO classification, particularly when:
- Multiple fibroids are present
- Surgical planning is required
- Ultrasound findings are equivocal
- Precise anatomic mapping is needed 3, 1, 6
MRI provides high-resolution, multiplanar visualization that allows more accurate assessment of the relationship between the fibroid and the endometrial cavity—critical for distinguishing Type 4 from Types 3 and 5 1, 6.
Treatment Implications
The FIGO classification directly influences management decisions 7, 5:
- Hysteroscopic myomectomy: Generally reserved for Types 0-2; may be technically feasible for some Type 3 fibroids but challenging for Type 4 due to limited intracavitary component 7
- Laparoscopic or abdominal myomectomy: More appropriate for Type 4 fibroids when fertility preservation is desired 5
- Uterine artery embolization (UAE): Appropriate option for Type 4 fibroids in properly selected patients 7, 8
- Medical management: Can be considered regardless of FIGO type when symptoms are mild 5
Critical point: Accurate FIGO classification on imaging reports is mandatory for appropriate treatment selection and surgical planning 3, 1. Radiologists should explicitly state the FIGO type in structured reports to guide clinical decision-making.