A myxoma is a benign, jelly-like tumour that is made up of soft mucous-like material and loose fibrous strands. They usually occur singly, and can grow to be quite large. The commonest site for a myxoma to grow is under a person's skin; usually in the limbs or the neck. However, they can also develop in the abdomen, bladder or bone.
Very rarely a myxoma will develop in the heart; an atrial myxoma. This can cause a lot of problems, as it can block the flow of blood through the heart. They also predispose the blood to thrombolise (clot) around it. These clots can then 'fly off' into the systemic circulation, causing strokes and arterial emboli. A myxoma can be successfully treated with surgery.
Myxomatosis is a highly infectious disease seen in rabbits (but never humans) caused by a virus that stimulates large numbers of myxomas to develop throughout the body.