Also called a leiomyoma or fibromyoma (or myofibroma, for that matter), it is an encapsulated tumour made up of disorganised and irregular connective tissue. A uterine fibroid is benign, there may be one or many, they grow slowly, have unknown causes, and may or may not cause painful menses or mid-cycle bleeding. Much depends on where they are in the uterus and whether or not they extend far enough into the cavity to impair and thin out the endometrium. If they do, they cause distress.