In 2016, the consensus opinion from the International Deep Endometriosis Analysis (IDEA) group 32 was published, which clearly and systematically outlines the features of deep endometriosis by ultrasound: uterus anteverted-retroflexed uterus ('question mark sign') is often seen with severe posterior compartment deep infiltrating endometriosis deep endometriosis is strongly associated with adenomyosis nodules on the serosal surface of the uterus may appear as solid, hypoechoic masses.