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Bone Cancer X-rays in Dogs

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Bone Cancer in Dogs

If you suspect your dog has bone cancer, you might be interested in learning more about bone cancer x-rays in dogs. After gathering some history and a throughout physical examination, your vet most likely will suggest x-rays to confirm or rule out bone cancer in dogs. Bone cancer can affect various parts of the dog's body, but it tends to have a preference to affect a dog's legs. In this article we will be taking a look at how bone cancer is seen on x-rays, what x-rays reveal and some other information pertaining bone cancer x-rays in dogs.

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Bone Cancer Information 

Osteosarcoma is the most common type of bone cancer affecting dogs. To better understand bone cancer x-rays, it's important to first understand exactly how bone cancer affects a dog's bones.

Bone cancer is typically found in the bones of the legs of large dog breeds that are middle aged or senior, but can sometimes also affect younger dogs. It has a preference for the ends of the dog's bones--at a joint.

Typical signs of bone cancer in dogs is limping which may initially be intermittent but then progresses to constant over the course of 1 to 3 months. The limping takes place because of the inflammation of the periosteum (connective tissue enveloping the bones)

Some dogs may also develop visible swelling which is indicative of the expansion of cancer into the surrounding soft tissue.

Bone cancer is a very painful condition as the cancer erodes the bone and the bone ends up being destroyed from the inside out. As the bone gets destroyed, the body attempts to fix the issue by creating tumurous bone, but the tumurous bone is not as strong as normal bone. Because tumourous bone is frail, it can be prone to fracturing, in what in medical terms is known as a "pathological fracture."

X-Rays for Dog Bone Cancer

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When a vet suspects bone cancer or wishes to rule it out, he or she will request to have x-rays done (multiple views are often needed). X-rays are usually done without sedation, but if the dog is particularly fractious or won't stay still, the vet may need to use sedatives to get good views and prevent the dog from feeling pain when he's being positioned for various x-rays.

Once x-rays are done, the vet will look for specific signs of bone cancer. In particular, the vet will look for lytic lesions, basically, signs of destruction of an area of bone due to the cancer. In simple words, these areas suggest that the bone is being eaten away.

There are two different patterns noticed. The sunburst pattern, as the name implies, shows rays radiating out from a central disk, while the Codman's triangle shows a triangle which is indicative that the periosteum has been raised due to the tumor.

On top of showing signs of destruction of the bone, x-rays will also show new bone proliferation, which consists of the tumerous replacement bone mentioned earlier.

"It requires approximately 50% of the bone per unit area to be destroyed before it is visible on radiographs...The more lysis that is present, the easier it is to see on radiographs. Also, by the time lysis is seen on a radiograph, the lesion is quite severe."~Dr. Anthony Pease, veterinary radiologist

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When Things Get Complicated 

In most cases, x-ray are effective in making the diagnosis of bone cancer due to its distinctive signs. The signs of bone cancer seen on x-rays are quite classic, but sometimes there may be complicating factors that may blur things.

If the x-ray does not produce distinctive signs but the vet is still suspicious of bone cancer, he or she may recommend having the x-rays reviewed by a board certified veterinary radiologist. Yes, for those curious to know, there are veterinarians specializing in x-rays and their interpretation.

In some cases, a bone biopsy may be needed for accurate diagnosis. In order to get a sample, a special needle will go through the skin and get out a core sample of the tissue. The sample is then sent to a pathologist for review. You and your vet will have to evaluate the pros and cons of getting a bone biopsy done.

In some cases, vets may suggest to get an aspirate and cytology done on joint fluid if there happens to be an increase in joint fluid or joint "space." This can be very helpful and its main advantage is that it is less invasive then a bone biopsy, observes veterinarian Dr. Kara. 

" Although biopsies can be performed, and may afford peace of mind to the owner prior to amputation, a small bone biopsy may reveal reactive bone that clouds a definitive diagnosis and the biopsy tract can create a weak point prone to pathologic fracture."~Dr. Kim A Selting, veterinary oncologist

Importance of Chest X-Rays

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If your vet notices signs of bone cancer on x-rays, don't be surprised if he or she also suggests to have chest x-rays done. Bone cancer is know for spreading to other body parts (metastasis), in particular the lungs.

By the time a dog is showing signs of limping, a certain level of metastasis is already taking place. "Osteosarcoma is highly metastatic and 90% of affected dogs are assumed to have metastatic disease at the time of diagnosis" points out Dr. Kim A. Selting, a veterinarian specializing in oncology.

Chest x-rays can reveal the rate at which the cancer in spreading. In most cases, no signs of cancer are seen in the lungs because the newly formed tumors are too minuscule to be detected (micrometastasis). If we look at statistics, signs of metastatic disease on the lungs are only found in about 10 percent of cases initially with 90 percent of dogs not showing any nodules on the lungs at the time of diagnosis.

Chest x-rays are therefore important prognostic factors. When there are no signs of cancer in lungs, amputation along with chemo can delay the development of systemic metastasis, with 1 year dog bone cancer survival rates of approximately 50 percent.

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References:

  • DVM360: Osteosarcoma: new tricks for old dogs (Proceedings)
  • DVM360: Radiography of bones: It's not just black and white (Proceedings)

Photo Credits:

  • Dog osteosarcoma Codman triangle Source: Ajimsha619 - Wikipedia Creative Commons Attribution-Share Alike 3.0 Unported license

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