What are Bone Cysts?

Bone cysts are benign bone lesions that occur at the ends of the long bones, which are fluid-filled. There can be multiple lesions, and they can be present on more than one bone. The cysts begin in the bone marrow cavity, and as they grow and expand, they weaken the bone and can even lead to fracture. (show rads)

Who gets Bone Cysts?

Bone cysts occur most commonly in young, large-breed dogs. Most dogs that develop bone cysts are under one year of age. Breeds affected included the German Shepherd, Weimaraner, Irish Wolfhound, Afghan hound, Saluki, Great Dane, and Doberman Pinscher.

What are the Signs of Bone Cysts?

Most bone cysts do not cause clinical signs until they reach a fairly large size. The most common sign is lameness. A swelling of the bone that is painful when direct pressure is applied may be noted. Stiffness of the nearest joint may also be present, or the animal may show severe pain and swelling due to a pathologic fracture at the site of the cyst.

How are Bone Cysts Diagnosed?

Diagnosis is made using radiographs. The radiographic findings are a benign, expansile, radiolucent area at the end of the affected bone. The cortex is thinned by the expanding cysts, and if a pathologic fracture has occurred, this will be evident on the x-rays as well. Because the radiographic findings of bone cysts can look very similar to those of bone cancer, a biopsy is necessary to make a definitive diagnosis. (rads – compare cysts vs. cancer)

Why did my Dog get Bone Cysts?

There are two types of bone cysts, and multiple causes. Simple (unicameral) cysts can be caused by trauma, blood clot formation, increased numbers of osteoclasts (cells that are responsible for breaking down and remodeling bone), obstruction of blood flow in the bone, or fluid accumulation within the bone. Aneurysmal bone cysts are a result of a traumatic event to the blood vessels within the bone. This leads to the formation of an abnormal connection between an artery and vein, and increased blood supply within the marrow cavity erodes the bone, causing a cyst to form.

How are Bone Cysts Treated?

The earlier bone cysts are diagnosed and treated, the better. If left untreated, they can lead to fracture of the bone. Surgery is required to treat the condition, and there are several surgical techniques used. In some cases, the affected bone is removed. This works well when the lesions are present on the lower half of the ulna; dogs that have this piece of bone resected recover normally and usually have no signs of lameness. A bone screw is utilized in reattaching the end of the ulna to the wrist. Another option is curettage, in which the inside of the bone cysts is scraped out, and then filled with bone graft. However, this procedure is less successful in treating aneurysmal bone cysts specifically. A less commonly used treatment involves filling the cyst with a compound called methyl methacrylate, also known as bone cement.

Can Bone Cysts be Prevented?

Because the precise cause of the condition is unknown, there are currently no preventative measures.

What is the Prognosis for my Dog with Bone Cysts?

Removal of the affected bone is usually curative. Curettage and bone grafting of simple bone cysts give a favorable prognosis. Aneurysmal bone cysts respond better to resection of the affected bone.