There are many causes of exophthalmos, however, the majority of thickened cases are due to Graves' disease in adults. MR provides optimal imaging of the orbits, with coronal and axial planes obtained with the patient's head in the neutral position. CT can also be used for orbital imaging by utilising thin slices (3mm) in the axial and direct coronal planes. The most common presentation is bilateral and symmetric ocular muscle enlargement with preference for the inferior and medial rectus. Bilateral asymmetric and occasionally unilateral involvement can also occur (Fig. 24.23).Idiopathic inflammation or ΓÇÿinflammatory pseudotumourΓÇÖ is another frequent cause of exophthalmos which often causes ocular muscle enlargement. Involvement is usually unilateral and tends to involve the muscles' tendinous insertion into the globe or may even present as an orbital mass. Other causes for exophthalmos are usually unilateral and include benign and malignant tumours (See Neurofibroma (MRI)), vascular malformations, carotid-cavernous fistula, or cavernous sinus thrombosis.
Fig. 24.23a Endocrine ophthalmopathy. Coronal Tl-weighted MR image showing extraocular muscle enlargement of the superior rectus, lateral rectus and inferior rectus of the right orbit. Enlargement of the medial rectus in the left orbit is also present.
