Hailey Bieber Shows Her Ovarian Cyst “the Size of an Apple” - E! NEWS

Endometriosis, according to the Mayo Clinic, occurs when uterus tissue grows outside the uterus, while PCOS—Polycystic ovary syndrome—is the development of cysts along the outer edge of the ovary. In Hailey's case, she didn't provide information about the nature of her cyst, but instead detailed how it makes her feel.

"I feel great," she said in a YouTube video

"The biggest thing I feel, honestly, is I just feel really relieved that we were able to figure everything out, that we were able to get it closed, that I will be able to just move on from this really scary situation and just live my life."