You would think that endometriosis always looks the same under the microscope, right? Well, no. Even after a biopsy and under the microscope, this disease doesn't always look the same, even in the same woman.
To diagnose this disease, the endometrial tissue, glands, and stroma must be present in the wrong place. But, in 30 to 50 percent of cases, the biopsy fails these criteria. How can this be? Several reasons may be possible.
t The surgeon doing the biopsy may just miss the real lesion. An area of endometriosis has many tissue variations. The inflammatory process can cause a change in color and distortion of the anatomy. And an area at the edge that looks good to biopsy may just be a reaction to the disease process and not the actual endometrial implant. The actual lesion may be much deeper and not visible. The surgeon doesn't want to cause harm while diagnosing the problem, so he may not biopsy deeply enough to reach the actual active endometriosis.
t The surgeon may not recognize the active areas. The textbooks describe classic endometriosis as black, stellate (star-shaped) lesions. But this definition is only for the end stage of the disease, so the biopsy may only contain scar tissue and old inflammatory cells and debris, not endometriosis. The surgeon may not even recognize the active areas because they may be too small, hidden, or unusual in appearance. Sometimes the earliest lesions are clear and hard to see. Or the surgeon may biopsy red areas that are actually bruises from the instruments.
S The pathologist doesn't see any glands or stroma. Endometriosis implants can become so distorted that the pathologist can't see any glands or stroma. The only evident glands are scattered and distorted, separate from any recognizable stroma. Pressure from the retained menstrual blood can squeeze the cells, making an area look different from endometrium. Imagine a shag carpet squashed so flat that its pile looks like part of the backing; this view is similar to what the pathologist may see.
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