A distinction is made between superficial lesions and deep infiltrating endometriosis.
In the majority of women with endometriosis the lining of the uterus found in the pelvis has only implanted superficially. These lesions may present as raised black or brown lesions, white discolouration, red “flame-like streaks”, clear blisters, small red blisters, bluish lesions, or yellow patches.
Deep Infiltrating Endometriosis
In about 20% of women, the body will not just allow the lining cells to implant in the pelvis, but also to infiltrate mainly into bowel, bladder, the vagina, and ligaments behind the uterus (uterosacral ligaments). This form of the disease is called deep infiltrating endometriosis (DIE). Deep infiltrating endometriosis causes usually more damage of the normal pelvic anatomy and is generally significantly more difficult to treat. Because lesions of endometriosis infiltrate into ligaments, vagina, bowel and bladder, adhesions can occur between organs such as the bowel and the uterus or the uterus and the ovaries.
What Ultrasound Can and Cannot Diagnose
“Superficial lesions” of endometriosis can never be diagnosed on ultrasound as these lesions have no real mass only colour, which cannot be detected with ultrasound. However, indirect evidence of suspicion of superficial endometriosis may occur because of localised tenderness or limited ovarian mobility on transvaginal ultrasound examination. The lesions look like small brown “blood splatters” which are implanted on various areas in the pelvis. These lesions can only be seen on laparoscopy. They are generally easy to remove. Special pre-operative measures are rarely required. They can however cause as much or more pain than some deep infiltrating lesions.
“Deep infiltrating endometriosis” causes usually more damage of the normal pelvic anatomy. Because lesions of endometriosis infiltrate into ligaments, bowel and bladder, a little ‘clump’ or ‘nodule’ is formed, which does have mass and can be detected with ultrasound. Also the adhesions that can occur between organs such as the bowel and the uterus or the uterus and the ovaries can be seen with ultrasound.
Often when deep infiltrating endometriosis is unexpectedly found at laparoscopy, without a pre-operative diagnosis with ultrasound, the removal of endometriosis cannot be completed as special preparation is required to allow removal of such lesions. The patient needs to take bowel preparation to allow surgery on the bowel, and often it is preferable to have a colorectal surgeon present at the surgery. If these lesions are diagnosed pre-operatively, the necessary preparations can be made prior to starting the first laparoscopy and repeat surgery can be avoided.
The larger the lesion, the easier it is to see on ultrasound, but in the hands of experienced imaging specialists, lesions of only a few millimetres can be diagnosed.
In summary, an ultrasound can never completely rule out endometriosis because the superficial type of endometriosis cannot be diagnosed with ultrasound. A laparoscopy may still be required to rule out endometriosis if symptoms are significant. But if the ultrasound was normal, there is a good chance that even if endometriosis is found at laparoscopy, it will be possible to complete the removal of most lesions. DIE on the other hand can rarely be removed at first surgery, unless its presence was known pre-operatively. Because ultrasound can diagnose these lesions, the surgery can be planned better and repeat surgery is less commonly necessary.