Adenomyosis, also known as endometriosis interna, is a uterine condition that causes tissue from the inner layer of the uterus (endometrium) to grow in its muscle layer (myometrium). The causes of this condition are unclear, but we know that it is dependent on the hormone estrogen. Amongst the factors that increase the chances for it to develop, we can find having had at least one pregnancy, and previous surgery to the uterus (C-section, D&C, hysteroscopy, etc.). It is associated with age as well, especially in women over 40. Certain types of adenomyosis can only me detected using special techniques such as 4D ultrasound or MRI. In the mildest cases, there exist few treatments with proven effectiveness, and there is still no proof that it diminishes the pregnancy rates of patients. However, in severe cases like T-shaped uteri, it requires surgery through hysteroscopy.