Leiomyoma Classification Systems

Leiomyoma Classification Systems

Malcolm G. Munro MD, FRCSC, FACOG

University of California, Los Angeles, USA

Key Points

A

  • Classification of leiomyomas is important for research, teaching, and to help with clinical evaluation and to determine clinical care.
  • The "L" in FIGO's AUB System 2, the PALM-COEIN system, stands for "Leiomyoma"
  • The FIGO Leiomyoma classification system has three tiers: The first is  simply the presence of a leiomyoma in the uterus
  • The second tier delineates submucous (sm) versus "other" (o), referring to leiomyomas not in contact with the endometrium.
  • The third tier categorizes all leiomyomas according to their relationship to the endometrium and the uterine serosa. In general, these comprise submucous myomas (Types 0, 1, 2, 3 and hybrid myomas eg type 2-5) subserous myomas (Types 5, 6, 7 and hybrid myomas), and intramural myomas (Types 3 & 4)
  • Types 2, 3, and 4 myomas should have their outer free margin documented (in millimeters) to facilitate decisions regarding procedural interventions.
  • A second leiomyoma classification system, the STEP-W system, is designed for surgical planning of myomectomy and in addition to the FIGO elements, considers leiomyoma size, location in association with the endometrial cavity other features.


The FIGO Leiomyoma Classification System

Clinical evaluation of the uterus can be difficult - relatively small submucous leiomyomas may be clinically relevant but not detectable on manual examination, while subserous tumors may be palpable but not clinical important. As a result, imaging is an important aspect of managing women with uterine leiomyomas.

The FIGO system for categorizing leiomyomas was first published in 2011 and revised in 2018.  The submucous tumors, thought to be most important in causation of AUB and infertility, are Types 0, 1, and 2, and also include Types 2-5,  3, and 3-5. Type 4 tumors are entirely surrounded by myometrium, while Types 5, 6, and 7 are in contact with the uterine serosa but not with the endometrium. Type 8 tumors exist outside the uterine corpus, most commonly in the uterine cervix.


This system was designed for several purposes. The first was to inform the design and interpretation of basic, translational, and clinical research. In this way, similar types of leiomyomas can be evaluated in disparate institutions and research environments for symptoms, endometrial molecular and genetic expressions, and the response to both medical and procedural interventions. Such an approach can facilitate the process of meta analysis in a fashion that may accelerate the proof or rejection of a research hypothesis. These types of results can then inform the clinician regarding relationships of different FIGO phenotypes to clinical manifestations, and, therefore, to the types of therapy, if any, that may be effective for a given individual. Finally, the system can be used to facilitate training of medical students, residents/registrars, and fellowship trainees.

The STEP-W (Lamar) System

Classification of leiomyomas requires the use of appropriate imaging techniques, which comprise ultrasound, sonohysterography, and magnetic resonance imaging (MRI). Hysteroscopy has a role but the accuracy of hysteroscopic classification is largely limited to Type 0 and 1 tumors, as, aside from very small lesions, Type 2 tumor relationship to the serosa, and distinguishing them from Type 2-5 lesions is difficult. Furthermore, hysteroscopy cannot detect other categories, including Type 3 leiomyomas.


FIGO's second level system categorizes two basic categories, those with at least one sub mucous myopia (Level 0, 1, 2, 3, 2-5, or 3-5) called "SM", and those with leiomyomas, all of which are not in contact with the endometrium called "O". This system is designed to help distinguish tumors that are thought to contribute to infertility or AUB from those likely unrelated to those symptoms

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