The etiological basis of proptosis can be inflammatory, vascular, or infectious. In adults, thyroid orbitopathy is the most common cause of exophthalmos. In children, unilateral proptosis is often due to an orbital cellulitis, and, in bilateral cases, neuroblastoma and leukemia are more likely.

The etiology of the thyroid-related orbitopathy is an autoimmune-mediated inflammatory process of the orbital tissues, predominantly affecting the fat and the extraocular muscles.