What are the FIGO (International Federation of Gynecology and Obstetrics) types of uterine fibroids as seen on ultrasound?

FIGO Classification of Uterine Fibroids on Ultrasound

The FIGO (International Federation of Gynecology and Obstetrics) classification system categorizes uterine fibroids into 9 types (0-8) based on their relationship to the endometrium, myometrium, and uterine serosa, with ultrasound serving as the first-line imaging modality for this assessment. 1, 2, 3

FIGO Classification System Overview

The FIGO system divides fibroids into three main anatomical categories with specific subtypes 2, 3, 4:

Submucosal Fibroids (Types 0-2)

• Type 0: Pedunculated intracavitary fibroid with no myometrial extension—entirely within the uterine cavity 2, 3, 4
• Type 1: Submucosal fibroid with <50% intramural extension—more than half protrudes into the cavity 2, 3, 4
• Type 2: Submucosal fibroid with ≥50% intramural extension—more than half remains within the myometrium 2, 3, 4

Intramural Fibroids (Types 3-5)

• Type 3: 100% intramural but contacts the endometrium, causing distortion of the uterine cavity 2, 3, 5
• Type 4: Pure intramural fibroid with no contact with either endometrium or serosa 2, 3, 4
• Type 5: Subserosal fibroid with ≥50% intramural component—more than half remains within the myometrium 2, 3, 4

Subserosal Fibroids (Types 6-7)

• Type 6: Subserosal fibroid with <50% intramural extension—more than half protrudes beyond the serosa 2, 3, 4
• Type 7: Pedunculated subserosal fibroid attached to the uterus by a stalk 2, 3, 4

Other Location (Type 8)

• Type 8: Fibroids in atypical locations including cervical, broad ligament, or parasitic fibroids 2, 3, 4

Ultrasound Assessment Protocol

Transvaginal ultrasound (TVUS) combined with transabdominal ultrasound (TAUS) and Doppler is the recommended first-line imaging approach, achieving 90-99% sensitivity and 98% specificity for fibroid detection and classification. 1, 6

Key Ultrasound Features to Document

• Location: Specify FIGO type based on relationship to endometrium and serosa 2, 3
• Number: Count all visible fibroids, noting if too numerous to count individually 2, 3
• Size: Measure maximum diameter in three orthogonal planes for each significant fibroid 2, 3
• Echogenicity: Describe as hypoechoic (most common), isoechoic, or hyperechoic relative to myometrium 2, 3
• Calcification: Note presence of acoustic shadowing from calcified areas 1, 2
• Vascularity: Use color Doppler to assess peripheral rim vascularity and identify feeding vessels 1, 6

Enhanced Ultrasound Techniques

• Saline infusion sonohysterography (SIS) improves visualization of submucosal fibroids (Types 0-2) and shows excellent agreement (kappa 0.80) with hysteroscopy for precise classification 6, 2
• 3D ultrasound provides volumetric assessment and better delineation of fibroid-endometrial interface 4
• Doppler imaging demonstrates the "bridging vessel sign" (interface vessels between uterus and fibroid) that confirms subserosal fibroids rather than extrauterine masses 1

When to Upgrade to MRI

MRI should be obtained when ultrasound findings are equivocal, when precise surgical planning is required, or when fibroids are too numerous to accurately map by ultrasound alone. 1, 6, 3

MRI is superior for 1, 6, 3:

• Differentiating Type 2 from Type 3 fibroids when the endometrial interface is unclear
• Mapping multiple fibroids (>4-5) for surgical planning
• Distinguishing fibroids from adenomyosis or atypical leiomyomas
• Assessing fibroid viability before uterine artery embolization

Clinical Significance of FIGO Classification

The FIGO type directly determines treatment options 7, 8:

• Types 0-2: Amenable to hysteroscopic myomectomy 7, 8
• Types 3-7: Require laparoscopic or open myomectomy if fertility preservation desired 7, 8
• Types 2-5: Suitable for uterine artery embolization 1, 7
• Type 3: Particularly controversial regarding fertility impact—associated with 16.4% pregnancy rate versus 30.1% in women without fibroids, even without cavity distortion 1, 5

Common Pitfalls in Ultrasound Classification

• Misclassifying Type 2 versus Type 3: Use SIS to precisely determine if >50% or <50% of the fibroid extends into the cavity 6, 2
• Missing Type 0 pedunculated fibroids: These may appear as endometrial polyps; Doppler showing a vascular pedicle has 95-98% specificity for polyps versus fibroids 1
• Incomplete evaluation of large uteri: TAUS is essential when TVUS field-of-view is limited by fibroid size or uterine enlargement 1, 6
• Overlooking Type 8 cervical or broad ligament fibroids: These require different surgical approaches and are not suitable for standard myomectomy techniques 7