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Understanding the Complex Classification of Endometriosis
Endometriosis is a complex and enigmatic disease with unclear origins and pathogenesis, presenting a wide spectrum of subtypes and clinical manifestations. Over the years, numerous pathogenetic hypotheses and classification systems have been developed to better understand and manage this condition. Since 1973, clinicians have proposed 22 different classification systems for endometriosis, each designed to address various aspects of the disease, including symptom severity, surgical findings, and treatment outcomes.
The Evolution of Endometriosis Classification Systems
The revised American Society for Reproductive Medicine (rASRM) score is perhaps the most well-known classification system for endometriosis. Initially developed by the American Fertility Society in 1979 and revised in 1985 and 1997, the rASRM score is widely used due to its relative ease of application. This system assigns points to endometriosis lesions in the peritoneum and ovaries based on their size, as well as to adhesions on the ovaries and Fallopian tubes. Points are also given for partial or complete obliteration of the posterior cul-de-sac. The total score is then categorized into four stages of severity:
- Stage I (minimal): 1–5 points
- Stage II (mild): 6–15 points
- Stage III (moderate): 16–40 points
- Stage IV (severe): >40 points
While the rASRM classification is widely recognized, it has limitations, particularly in its ability to account for deeply infiltrating endometriosis (DIE) involving retroperitoneal structures.
The Enzian Classification
To address some of these limitations, the Enzian classification was introduced by the Scientific Endometriosis Foundation (SEF) in 2003 and 2005. This system is particularly useful for describing deeply infiltrating endometriosis and is organized into three compartments:
- Compartment A: Vagina and rectovaginal space (RVS)
- Compartment B: Uterosacral ligaments (USL), cardinal ligaments, and pelvic sidewall
- Compartment C: Rectum
In addition to these compartments, the Enzian classification includes a category for "far locations" (F), such as the urinary bladder (FB), ureters (FU), and other extragenital lesions (FO). It also accounts for the involvement of the peritoneum (P), ovaries (O), other intestinal locations (e.g., sigmoid colon, small bowel; FI), and adhesions involving the tubo-ovarian unit (T), as well as tubal patency.
This classification can be applied using both non-invasive methods (like TVS and MRI) and invasive methods (such as surgery), providing a comprehensive framework for evaluating endometriosis across different settings.
The Endometriosis Fertility Index (EFI)
In 2010, Adamson and Pasta introduced the Endometriosis Fertility Index (EFI), the only scoring system significantly associated with pregnancy outcomes in women affected by endometriosis. The EFI score is a clinical tool designed to predict an infertile endometriosis patient’s probability of achieving pregnancy with standard, non-IVF treatments following surgical staging. The EFI score is determined by combining the patient's history (50%), surgical findings at the completion of surgery (30%), and rAFS scores (20%).
The 2021 AAGL Endometriosis Classification System
The most recent addition to endometriosis classification is the 2021 AAGL Endometriosis Classification System. This system is an objective, anatomically derived, and user-friendly tool constructed from expert surgeon ratings of surgical difficulty. It establishes four stages that reliably describe the level of complexity of surgery required to completely treat observed disease, thus providing a more accurate and practical approach to managing endometriosis.
Conclusion
The classification of endometriosis remains a dynamic field, with each system offering unique insights into different aspects of the disease. From the widely used rASRM score to the more specialized Enzian classification and the prognostically valuable EFI score, these tools help clinicians diagnose, stage, and treat endometriosis more effectively. The latest developments, such as the 2021 AAGL Endometriosis Classification System, continue to refine our understanding of the disease, ultimately improving patient outcomes through more tailored and informed treatment strategies.