The only way to be diagnosed is by having a surgery to see what is actually there. Some women are found to have endo while having an op for something else in the tummy.
Some are diagnosed in a key hole op specifically looking for endo due to all their other symptoms.
Either way surgery is the one thing in common.
Symptoms can give clues to a lady having endo. and a scan that picks up blood filled endometrioma also hints at endo so too does finding that an ovary is stuck with adhesions in the wrong location.
With the big clues, you can safely say some one has suspected endo.
the surgery will identify where it is growing, how big each patch is, how deep it is growing, and also look for other damaging signs like scarring and adhesions. a surgery can also check on whether your fertility is looking good, looking under threat or already compromised and the tubes blocked up stopping the egg reaching the womb.
Even if the surgery shows nothing visible on surfaces and endo grows on surfaces of anything. There is another very similar condition called adenomyoisis which has much the same monthly cycle of pains, only this only grows inside the muscle walls of the uterus and is hidden from view in most cases.
It can show up on scans as tell tale lumpy muscle walls where the blood of a period is trapped in little lumps or blood blisters within the muscle tissue. Adeno can be removed entirely with a husterectomy to remove the uterus muscle walls containing the adeno cells.
Please push for a lap op it is the only way to be sure with endo. It really is nigh on inpossible to see all the endo locations even with an MRI as it is a surface growth speading sideways. not really 3 dimensions enough to show on scan.