10/27/2025
“One way or another”: Understanding different classifications of endometriosis
If you’ve been told you have “Stage I” or “Stage IV” endometriosis, you might wonder what that really means—and what it says about your pain, symptoms, or treatment options. The truth is, the “stage” of endometriosis doesn’t always match what patients experience. Someone with Stage I disease can be in severe pain, while another person with Stage IV might feel only mild discomfort. It is important to understand what your “stage” actually tells you—and what it doesn’t.
Where the Staging System Came From
The most commonly used system for describing endometriosis, developed by the American Society for Reproductive Medicine (ASRM), wasn’t designed to measure pain at all. It was originally created to help predict fertility outcomes by scoring the size, depth, and location of endometriosis lesions and adhesions (scar tissue) in the pelvis.
Under this system, patients are assigned a stage from I (minimal) to IV (severe). These categories depend on factors like how much tissue is affected and whether organs are bound together by adhesions. But they don’t take into account how deep lesions may go, how painful they are, or how they impact daily life.
Why Stage Doesn’t Equal Pain
Endometriosis pain is complex—it’s influenced by far more than what can be seen during surgery. Lesions can invade nerve pathways, cause widespread inflammation, and affect how the body processes pain signals.
It’s a paradox: some patients with focused areas of peritoneal endometriosis can experience intense, debilitating pain, while others with more widespread disease have little discomfort. In short, the stage of endometriosis is not a measure of how much you hurt.
A Newer Way to Classify Endometriosis
In recent years, specialists have moved away from relying solely on ASRM stages. Instead, they focus more on where and how the disease behaves—information that can be more relevant to symptoms and surgical planning. Endometriosis is now often described in three categories:
Peritoneal endometriosis: Superficial lesions on the lining of the pelvis and abdomen, called the peritoneum.
Deeply infiltrating endometriosis (DIE): Lesions that grow deeper into structures beneath the peritoneum such as the uterosacral ligaments, bowel, or bladder.
Ovarian endometriomas: Cysts of endometriosis in the ovaries filled with old blood, sometimes called “chocolate cysts.”
What This Means for You
Deeply infiltrating endometriosis (DIE): Lesions that grow deeper into structures beneath the peritoneum, such as the uterosacral ligaments, bowel, or bladder. Where is the disease located? How deep does it go? What organs are affected? Of course, some of this can only be confirmed with surgery. However, high-quality imaging can provide a very good sense of the extent of your disease. At initial consultations at Pacific Endometriosis and Pelvic Surgery, we perform a detailed pelvic ultrasound to evaluate for endometriosis, including deeply infiltrating disease and ovarian endometriomas. This allows us to discuss the likely “stage” or extent of endometriosis in practical terms. While we understand that your stage does not always correlate with the amount of pain you are experiencing, we use this information to have a thoughtful discussion about your symptoms and the next best steps for your care.
