Uterine fibroid. Coloured 3-D ultrasound scan of a submucosal fibroid (upper centre) of the uterus. 'Submucosal' means that the growth is beneath the mucous membrane (endometrium) that lines the inside of the uterus. A fibroid is a benign tumour of fibrous and smooth muscle tissue. Most fibroids do not require treatment, but some can cause bleeding, pain and other disorders. Large fibroids may need to be surgically removed. Ultrasound is a diagnostic technique that sends high frequency sound waves into the body via a transducer. The returning echoes are recorded and used to build an image of an internal structure. 3-D scanning uses computer technology to return more detailed images than conventional 2-D scans.