Uterine Fibroid Mapping: FIGO Types and MUSA Terminology
Why Combine FIGO and MUSA
When mapping fibroids in ultrasound protocols, standardized classification is important not only for size grading (small/large) but also for localization, structure, and nodule blood flow. The FIGO classification (2011) describes nodule location relative to uterine layers, while MUSA terminology (Morphological Uterus Sonographic Assessment, consensus 2015) standardizes the description of sonographic features of myometrium and uterine masses using grayscale, color/power Doppler, and 3D visualization.
FIGO Classification (2011)
The FIGO classification for localization of leiomyomatous nodules (types 0–8) is currently considered the standard for describing nodule location, and its use in protocols is preferred. It is part of the FIGO system (PALM-COEIN) for determining causes of abnormal uterine bleeding in non-pregnant women of reproductive age (Munro MG et al., 2011). The classical division into subserosal, intramural, and submucosal nodules is supplemented by specific FIGO type. [Note: detailed criteria for types 0–8 are not available in provided fragments]
MUSA Terminology for Nodule Description
MUSA was originally developed to describe myometrial lesions, including smooth muscle tumors of the uterus. It is used to describe tumor shape, margins, internal echogenicity, echo pattern, presence of cystic areas or calcifications, shadowing, and vascularization.
Echogenicity of solid lesions according to MUSA is described as:
| Feature | Variants |
|---|---|
| Echogenicity (homogeneous) | hypoechoic, isoechoic, hyperechoic |
| Echogenicity (heterogeneous) | mixed echogenicity, hyperechoic zones, cystic zones |
| Shadowing | peripheral, internal, fan-shaped |
| Nodule shape | regular (oval/round) or irregular (lobulated/spiculated) |
Vascularization Assessment
Vascularization is assessed using a semi-quantitative color scale: 1 — absent vascularization; 2 — minimal; 3 — moderate; 4 — abundant (marked) vascularization.
Nodule Sizes
There are no unified strict international size criteria. A common grading by diameter is: small — up to 2 cm; medium — 2–5 cm; large — 5–10 cm; giant — over 10 cm. Some sources and Russian clinical guidelines use the following division: up to 2 cm — small; 2–6 cm — medium; over 6 cm — large. In ultrasound protocols, it is preferable to report three specific nodule dimensions in mm and its volume rather than description in "weeks of pregnancy."
Clinical Significance
MUSA terminology is applied for differential description of uterine leiomyoma and uterine sarcoma, as well as for assessing inter-operator reproducibility of ultrasound findings (De Bruyn C et al., 2024). A standardized protocol combines FIGO localization with MUSA description of morphology and blood flow.
Frequently asked questions
Which classification for fibroid localization is considered standard?
The FIGO classification (2011) with nodule types 0–8; its use in ultrasound protocols is preferred for describing localization.
How is nodule vascularization described according to MUSA?
Using a semi-quantitative color scale: 1 — absent vascularization, 2 — minimal, 3 — moderate, 4 — abundant.
How is nodule echogenicity described according to MUSA?
As homogeneous (hypoechoic, isoechoic, or hyperechoic) or heterogeneous with mixed echogenicity, hyperechoic, or cystic zones; shadowing is separately noted as peripheral, internal, or fan-shaped.
How should fibroid size be properly documented in the protocol?
It is preferable to provide three specific nodule dimensions in mm and its volume rather than description in "weeks of pregnancy."
What is the purpose of MUSA in fibroid assessment?
To provide standardized description of sonographic features of myometrium and uterine masses, including differentiation of leiomyoma from sarcoma and assessment of reproducibility of ultrasound findings.