Imaging demonstrates enlargement of the muscle belly of one (or more) extraocular muscles typically with the involvement of tendinous insertions. Involvement of the tendinous insertion distinguishes the idiopathic orbital inflammation from thyroid-associated orbitopathy (TAO) in which the insertion point is spared. However, sparing of the anterior tendon does not exclude the diagnosis of idiopathic orbital myositis ⁷.

Additional inflammation can be seen in surrounding tissues, including the orbital fat, lacrimal gland, and optic nerve sheath.

It can appear as an infiltrative mass and extends outside of the orbit via superior or inferior orbital fissures. Extension into the cavernous sinus, meninges, and dura can occur. It is most commonly unilateral but can be bilateral in 25% of cases.