Zygomatic Bone Tumors in Dogs

Zygomatic or temporal bone tumors are members of a family of tumors of the skull known as multilobular osteoma and chondroma. These are the most common benign (noncancerous) bone tumors in dogs. The tumors are slow-growing and invasive and can lead to other problems unless they are removed. Some tumors have been known to become malignant, cancerous. Zygomatic bone tumors are benign growths that occur specifically on the face or skull around the jaw bone.

  1. Occurrence

    • Multilobular osteoma and chondroma are benign bone tumors that typically occur in dogs aged 15 months to 12 years, the average age being 7 years. Although these tumors are more common in medium-sized and larger dogs, no breed is more susceptible than another, and tumors occur equally in both sexes. The tumors can occur in the front sinus near the nose, behind the eye, along the jaw bone or can invade the brain.

    Characteristics

    • It is unclear whether these tumors are primary growths, arising in the skull itself, or if they are secondary growths, activated by other bones in the skull. Multilobular osteoma and chondroma are composed of normal bone and cartilage, well-supplied with blood vessels--highly vascularized. The tumors may extend into the soft tissues surrounding the bony growth.

    Signs and Symptoms

    • The most obvious sign of a zygomatic bone tumor is a hard mass in the area of the jaw. The tumor will appear as a deformity on the dog’s head or face. Tumor size can vary from 1 cm to 10 cm (1/3 inch to 4 inches). Because of its location, a zygomatic bone tumor can make it difficult for the dog to open his jaw. If the tumor invades the brain, the dog may have problems with his nervous system, including pain and difficulty walking.

    Diagnosis

    • The veterinarian will perform a physical examination of the bony area and take X-rays. If the nature of the tumor is not clear on the X-ray film, the veterinarian may need to perform a bone biopsy to make sure the growth is a benign zygomatic tumor.

    Treatment

    • The tumor must be surgically removed to prevent problems resulting from invasion of neighboring tissues, including the brain, tendons and nerves, leading to pain; nerve damage; and impaired mobility. If the tumor is not completely removed, it can grow back at the surgical site. Tumor removal also will improve the dog's appearance. These tumors have been known to become cancerous with resulting metastases to the lungs.