The top differential diagnoses of this skull tumor are osteosarcoma (OSA), chondrosarcoma (CSA), and multilobular osteochondrosarcoma (MLO).
OSA is the most common primary bone tumor of dogs and skull OSA accounts for < 3% of all OSA. Axial OSA carries a more favorable prognosis than appendicular OSA, and Tx consists of radiation and chemotherapy.
Chondrosarcoma is a malignant, cartilage-producing tumor, and the second-most common primary bone tumor. Unlike OSA, CSA is more common in the axial skeleton than appendicular skeleton. Surgery is the Tx of choice for CSA, with radiation therapy recommended for unresectable tumors.
MLO presents as a firm, fixed mass arising from the periosteum. Clinical signs are referable to location. Tx is surgical with unknown effects of chemotherapy and radiation.
Osteomyelitis is infection and inflammation of bone. Masticatory myositis is immune-mediated inflammation of the muscles of mastication.
Hypertrophic osteodystrophy is a developmental disorder of the metaphysis of long bones of young, growing dogs. Craniomandibular osteopathy is a proliferative bone disorder of growing terrier dogs that affects the mandible and tympanic bullae. Multiple cartilaginous exocytosis affects young dogs and cats: see multiple ossified protuberances arising from the surfaces of long bones.
Hemangiosarcoma is a tumor arising from endothelial cells. Meningioma is a benign, space-occupying tumor arising from the dura of the brain or spinal cord. Squamous cell carcinoma is a skin tumor that can result in firm, nodular, +/- erosive mass lesions. Rhabdomyosarcoma is a malignant primary muscle tumor.
Hypertrophic osteopathy is a paraneoplastic proliferation of long bones secondary to intrathoracic or intraabdominal tumors.
