What are the imaging findings of endometriosis on Ultrasound and MRI?
Endometriosis is defined as the presence of endometrial tissue outside the uterus, most commonly involving the ovaries, uterine ligaments, cul-de-sac, pelvic peritoneum, fallopian tubes, distal colon, and bladder. Endometriosis is commonly diffuse with scattered implants, but it can also be focal with a discrete endometrioma (also described as a “chocolate cyst” because of its appearance at pathology).
On US, a typical endometrioma presents as a unilocular or multilocular cystic lesion with homogeneous low-level echoes and no internal vascularity. In addition, the presence of ectogenic foci in the roll of a cystic mass that contains low level echoes would favor the diagnosis of endometrioma, and may be seen in one third of endometrioma. CT is not used commonly for evaluation of endometriosis, but it may visualize large endometriomas and complications such as rupture or bowel obstruction. On MRI, an endometrioma demonstrates T1-weighted hyperintensity that persists after fat suppression and T2-weighted hypointensity (also called “shading”). Another specific sign recently reported is the presence of more focal low T2-weighted signal intensity spots. Presence of multiple or bilateral high T1-weighted signal intensity ovarian lesions makes endometriomas more likely than hemorrhagic cysts. MRI also plays a role in revealing sites of deep fibrotic endometriosis involving structures such as the sigmoid colon, rectum, and cul-de-sac. Fibrotic endometriosis typically has low T2-weighted signal intensity and tethers adjacent structures.