Endometriosis is a chronic condition characterized by the growth of tissue similar to the uterine lining (endometrium) outside the uterine cavity. This misplaced tissue responds to hormonal fluctuations, causing inflammation, scar tissue formation, and pelvic pain. A standardized classification system measures the severity and anatomical spread of the condition. This system assigns a numerical score based on surgical findings to determine the disease stage.
Defining Peritoneal Endometriosis
Peritoneal endometriosis refers specifically to the presence of lesions on the peritoneum, the thin membrane lining the abdominal and pelvic cavity. This is often the most common type, where tissue adheres superficially to the surface of pelvic organs and sidewalls. Superficial lesions do not penetrate deeply into underlying tissue, distinguishing them from deep infiltrating endometriosis (DIE), where lesions penetrate more than five millimeters. Peritoneal endometriosis is also distinct from ovarian endometriomas, which are cysts within the ovaries. Implants are visually identified during laparoscopy, where their location, size, and appearance are documented.
The Standardized Scoring System
The severity of endometriosis is most commonly measured using the Revised American Society for Reproductive Medicine (rASRM) classification system. This point-based scale is the standard tool for staging the disease based on surgical observations. Numerical values are assigned to various surgical findings.
The score is calculated based on three main criteria: the size and location of implants, the extent of adhesions, and the involvement of the ovaries and fallopian tubes. Adhesions are bands of scar tissue that cause organs to stick together, scored based on whether they are filmy or dense. The total cumulative score determines which of the four stages the patient is assigned. This anatomical staging describes the disease’s morphology but does not always correlate with the patient’s experience of pain or other symptoms.
How Peritoneal Lesions Determine Stage
The characteristics of the peritoneal implants play a direct role in determining the rASRM score and the assigned stage. Peritoneal lesions are categorized by their size, and point values increase as the size of the lesion increases. For example, a superficial implant less than one centimeter receives a small number of points, while a larger implant receives a higher score.
The appearance of the lesion also contributes to the scoring, as implants can manifest in various colors, including white, red, black, or non-pigmented. Black lesions are often older, while red lesions are typically newer and more active.
Since superficial peritoneal lesions are not deeply invasive, they do not carry the high point values associated with ovarian endometriomas or dense adhesions. The maximum score assigned to the peritoneal component is significantly lower than the maximum score possible for ovarian involvement. Therefore, the presence of peritoneal endometriosis alone often results in a Stage I or Stage II classification.
The Four Stages of Endometriosis
The numerical score accumulated from the rASRM classification system places the disease into one of four distinct stages. Stage I (Minimal Endometriosis) is defined by a score of one to five points, typically involving a few isolated, superficial peritoneal implants and no significant adhesions. Stage II (Mild Endometriosis) is assigned six to fifteen points, indicating more numerous superficial implants with minimal involvement of the ovaries or fallopian tubes.
Stage III (Moderate Endometriosis) ranges from sixteen to forty points. This stage often includes multiple superficial and some deeper implants, small ovarian endometriomas, and more pronounced adhesions. Stage IV (Severe Endometriosis) is characterized by a score greater than forty points, involving numerous deep implants, large ovarian endometriomas, and extensive, dense adhesions that can distort the pelvic anatomy.