Obstetric and Gynaecological · Uterine leiomyoma reporting · 1.1

FIGO leiomyoma subclassification (types 0-8)

The FIGO three-tier system locating uterine leiomyomas as types 0-8 by their relationship to the endometrium and serosa, used to standardise reporting and guide hysteroscopic, surgical and interventional treatment selection.

Purpose

To provide a standardised, purely anatomical description of where each uterine leiomyoma sits relative to the endometrium and the serosa, within the leiomyoma ('L') component of the FIGO PALM-COEIN classification of abnormal uterine bleeding. The system does not grade size, number or vascularity; its value is that the assigned type directly predicts whether a lesion is hysteroscopically resectable, suitable for laparoscopic or open myomectomy, or a good target for uterine artery embolisation.

Type	FIGO tier-2 group	Anatomical descriptor and definition	Reporting and management implication
0	Submucous (SM)	Pedunculated intracavitary; entirely within the endometrial cavity with no myometrial component	Most amenable to hysteroscopic resection; state stalk width and craniocaudal position (prolapse risk)
1	Submucous (SM)	Submucosal with less than 50% of the lesion intramural	Usually hysteroscopically resectable in a single sitting
2	Submucous (SM)	Submucosal with 50% or more of the lesion intramural	Document outer free margin to serosa in millimetres; higher risk of incomplete resection, perforation and fluid overload, so a staged approach may be needed
3	Other (O)	Intramural with endometrial contact; entirely intramural but abutting the endometrium without cavity distortion	Endometrial contact is relevant to bleeding and fertility; document outer free margin
4	Other (O)	Intramural; entirely within the myometrium, contacting neither endometrium nor serosa	Typical target for myomectomy or uterine artery embolisation; document outer free margin
5	Other (O)	Subserosal with 50% or more of the lesion intramural	Report relationship to serosa; deeper myometrial defect at myomectomy
6	Other (O)	Subserosal with less than 50% of the lesion intramural	Laparoscopic approach usually feasible
7	Other (O)	Subserosal pedunculated; attached to the serosa by a stalk	Distinguish from a solid adnexal mass by identifying the bridging vascular stalk; consider torsion
8	Other (O)	Non-myometrial location, such as cervical, broad-ligament or parasitic leiomyoma	Specify the actual site in text; anticipate atypical or extrauterine arterial supply before embolisation
Hybrid (e.g. 2-5)	Transmural (SM and O)	Lesion contacting both endometrium and serosa; two digits separated by a hyphen, the first for the endometrial relationship and the second for the serosal relationship	Report both digits; predicts a transmural defect at myomectomy

How to use it

The system has three tiers: first, whether a leiomyoma is present at all; second, submucous (SM) versus 'other' (O); and third, the numerical type 0-8 based on the relationship to endometrium and serosa. 'Other' is therefore a formal FIGO tier-2 label for types 3-8, not a vague catch-all, and should be paired with the anatomical descriptor (intramural, subserosal) in a report.
The submucous versus other split exists because submucosal location is most strongly associated with abnormal uterine bleeding and is the main determinant of hysteroscopic resectability.
Types 1 and 2 are separated by the intramural proportion: type 1 has less than 50% intramural extension and type 2 has 50% or more, so type 2 carries the greater risk of incomplete hysteroscopic resection.
For types 2, 3 and 4 the outer free margin between the lesion and the serosa should be documented in millimetres, because this margin governs the safety of hysteroscopic and other procedural approaches.
The classification is anatomical only: it does not encode size, number, vascularity or degeneration, so a complete report must add three-dimensional size, lesion number, position and uterine volume alongside the FIGO type.

Common mistake

Assigning a single number to a lesion that reaches both the endometrium and the serosa; such transmural lesions require hybrid two-digit notation, and reporting one surface only underestimates the surgical defect. Two further recurrent errors are confusing types 1 and 2 by quoting the submucosal rather than the intramural proportion, and reporting a type 7 pedunculated subserosal fibroid as an adnexal mass because the bridging vascular stalk was not sought.

Exam pearl

Submucous group = 0, 1, 2; everything else is FIGO 'other' = 3 to 8. Type 3 touches the endometrium, type 4 touches nothing, type 5 and 6 are subserosal split at 50% intramural, type 7 is pedunculated subserosal, type 8 is non-myometrial (cervical, broad ligament, parasitic).

Viva questions

What does the 'L' in PALM-COEIN represent, and how is it structured?: L stands for leiomyoma, one of the structural PALM causes of abnormal uterine bleeding. It has three tiers: presence of a leiomyoma, then submucous versus other, then the numerical type 0 to 8 based on the lesion's relationship to the endometrium and the serosa.
Why are types 3 to 8 grouped as 'other'?: Because the classification was designed for abnormal uterine bleeding, and submucosal lesions are the ones most strongly associated with bleeding and amenable to hysteroscopic treatment. Everything without a submucosal component falls into the FIGO 'other' group, which anatomically comprises intramural types 3 and 4, subserosal types 5 to 7, and non-myometrial type 8.
Define FIGO types 0, 1 and 2.: All are submucous. Type 0 is pedunculated and entirely intracavitary with no myometrial component, type 1 has less than fifty per cent intramural extension, and type 2 has fifty per cent or more intramural extension.
How do you distinguish type 3 from type 4?: Both are entirely intramural. Type 3 abuts the endometrium without distorting the cavity, whereas type 4 contacts neither the endometrium nor the serosa.
For which types must the outer free margin be documented, and why?: Types 2, 3 and 4. The distance in millimetres from the lesion to the serosa determines the safety of hysteroscopic resection and the risk of perforation, and guides the choice of procedural approach.
What is a hybrid leiomyoma and how is it written?: A lesion contacting both the endometrium and the serosa. It is written as two numbers separated by a hyphen, for example 2-5, where by convention the first digit describes the endometrial relationship and the second the serosal relationship.
What is the pitfall with a type 7 leiomyoma, and what does type 8 mean for an interventional radiologist?: A pedunculated subserosal fibroid can be mistaken for a solid adnexal mass; the bridging vascular stalk on Doppler or MRI confirms uterine origin. Type 8 lesions such as cervical, broad-ligament or parasitic fibroids sit outside the myometrium and may derive supply from vessels other than the uterine arteries, which must be sought before embolisation.
What does the FIGO leiomyoma system deliberately not capture?: It is purely anatomical. It does not encode fibroid size, number, vascularity or degeneration, so the report must add three-dimensional measurements, lesion count, position and uterine volume for treatment planning.