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Bone Cancer of the Skull in Dogs

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Bone Cancer of the Skull in Dogs

Bone cancer of the skull in dogs is not a very common type of cancer, considering that the primary locations for dog bone cancer are the long bones of the legs. However, bone cancer of the skull in dogs is not unknown and there are several forms of this type of cancer. If your dog was diagnosed with bone cancer of the skull, it's important to learn more on what to expect and what treatment options are available. Some forms of bone cancer of the skull in dogs are more aggressive than others.

dog skull anatomy

Bone Cancer of the Skull in Dogs 

Bone cancer may affect several bones found in the dog's skeleton. In order to better categorize the bones of the skeleton, the skeleton is often divided into two major regions, the appendicular skeleton and the axial skeleton.

The axial skeleton comprises bones found in the central axis, namely the skull, vertebrae, ribs and sternum. The appendicular skeleton, on the other hand, comprises the dog's limbs and all the attachment points for the limbs.

A dog's skull is composed by 50 bones which can be divided in three categories: bones of the cranium (14 bones), bones of the face and palate (21 bones) and bones of the hyoid apparatus and middle ear (15 bones).

Bone cancer of the skull may be detected by x-ray, but the definite diagnosis that can differentiate the different forms or bone cancer can mainly be obtained through a bone biopsy. A bone biopsy typically requires a small amount of sedation or a very short anesthesia. Ideally, a biopsy of bone found on the skull is best if done by a board-certified surgeon.

Bone cancer affects mostly middle-aged to older dogs. However, there have been cases of certain bone cancers affecting dogs as young as 6 months.

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Osteosarcoma Bone Cancer of the Skull in Dogs 

Osteosarcoma (OSA) has a tendency to affect the major weight-bearing bones of the legs. It is estimated that more than 75 percent of osteosarcoma occur in the long bones, while the remaining occur in the axial skeleton.

When the axial skeleton is involved, osteosarcoma primarily affects the skull, upper and lower jaws, and ribs. When osteosarcoma affects the flat bones such as those in the skull, affected dogs typically present localized swelling.

Osteosarcomas tend to grow fast and spread rapidly to other organs, in particular to the lungs. X-rays of the lungs should be done to check for signs of the cancer spreading. Signs of spread to the lungs are not visible at least until the nodules in the lungs are larger than 6 to 8 mm.

Treatment for osteosarcoma of the skull comprises surgery with aggressive removal of the tumor. However, despite removal, control of the tumor is difficult and life expectancy is poor, generally with a median survival time of 4 months.

"Axial skeleton OSA is locally aggressive and median survival times commonly fall around 4 months...It is thought that OSA of the flat bones of the skull has a lower metastatic behavior than other skeletal locations."~Dr. Kim A. Selting

Chondrosarcoma Bone Cancer of the Skull in Dogs 

Chondrosarcoma is the second most common type of bone cancer affecting dogs. The word chondrosarcoma is derived from the word "chondro" meaning related to cartilage and "sarcoma" meaning fleshy growth. A chondrosarcoma is therefore defined as being a cancer that derives from transformed cells responsible for producing cartilage.

This form of bone cancer mostly affects the flat bones, particularly the nasal turbinates (28 percent), ribs (17.5 percent), and facial bones (9 percent), specifically the upper jaw, lower jaw and orbit. This type of cancer is not usually found in the dog's limbs.

The most frequently reported symptom found in dogs affected by chondrosarcoma of the facial bones were a mass or swelling on top the affected area.

When x-rays of taken, it is difficult to differentiate chondrosarcomas from osteosarcomas. The only true way to differentiate the two is by bone biopsy.

Chondrosarcomas are slow growing cancers that tend to be less likely to spread to other body parts such as the lungs as osteosarcomas tend to. Generally, the rate of spread (metastasis) to other body parts is approximately 17 percent.

"The most frequently reported clinical sign in dogs with chondrosarcoma involving the facial bones (included all the bones of the skull not associated with the nasal cavity or paranasal sinuses) is a mass or swelling over the affected area."~Journal of Veterinary Science

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Multilobular Osteochondrosarcoma

Multilobular osteochondrosarcoma (MLO) although uncommon is the most common tumour found on the dog's skull. These tumors tend to be more of the compressive rather than the invasive types that spread to other organs.

An MLO tumor tends to affect the dog's upper or lower jaw or skull and rarely affects the dog's ribs or pelvis. Usually, a firm, slow growing bone mass is detected. MLO tend to be locally invasive but they have the potential to compress and invade the dog's brain.

This type of tumor needs to be differentiated from other types of tumors by a bone biopsy. When biopsied, this type of bone cancer tends to have a characteristic multilobular appearance hence its name.

"MLO's exhibit characteristics of both benign and malignant tumors-- they are relatively slow-growing and well-defined, but often cause extensive regional destruction and osteolysis, with metastases possible."~ The Veterinary Cancer Center 

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References:

  • Popvitch CA, Weinstein MJ, Goldschmidt MH, Shofer FS. Chondrosarcoma: a retrospective study of 97 dogs (1987-1990) J Am Anim Hosp Assoc. 1994;30:81–85
  • J Vet Sci. 2007 Mar; 8(1): 99–101.Primary chondrosarcoma in the skull of a dog, Heejaung Kim, Munekazu Nakaichi, Kazuhito Itamoto, Yasuho Taura

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