Coloured magnetic resonance imaging (MRI) scan of the pelvis of a 68 year old female with a large fibroid (purple), measuring more than 8.5 centimetres in diameter, in her uterus. A fibroid is a fibrous benign tumour originating from muscular tissue. Most do not require treatment, but some can cause bleeding, pain and other disorders. Large fibroids may need to be surgically removed.