Endo is not detected by ultrasound
Although this is generally true, my endo was effectively picked up by u/s - they discovered one of the ovaries was 'fixed' to the pelvic wall, and indicated that was likely to be endo adhesions. They were right - this was then confirmed by lap and the adhesion / endoremoved.

Oh, did anybody read this exciting article the other day???
Simple test to detect endometriosis