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Findings: Axial and coronal noncontrasted CT images through the orbit demonstrate thickening of the extra-occular muscles, specifically the superior rectus and medial rectus. In addition, there is decreased attenuation throughout the muscle belly suggestive of fat infiltration. These findings are more pronounced within the left orbit. In addition, there is an increased amount of intra-orbital fat.
Diagnosis: Thyroid orbitopathy.
Discussion: Thyroid ophthalmopathy is most commonly seen in middle aged females and can present with exophthalmos, diplopia as well as restriction in eye movements.
There is commonly involvement of the extra-occular muscles with sparing of the tendinous insertions. This is an important distinction in differentiating thyroid orbitopathy from pseudotumor. The inferior rectus muscle is most commonly involved followed by the medial rectus, superior rectus, and lateral rectus respectively. Although involvement of the muscle belly is most commonly enlarged, low density areas within the muscle can sometimes be noted. This is indicative of lymphocytic infiltration. Other common findings include increased orbital fat as well as enlargement of the lacrimal glands.
Findings can be unilateral or bilateral. However, the majority of patients demonstrate bilateral involvement radiographically despite unilateral clinical findings.
References:
Rootman J, Editor: Disease of the Orbit. Philadelphia: J.B. Lippincott Co.; 1998.
Som P, Bergeron RT. Head and Neck Imaging, 2nd Edition, St. Louis: Mosby Yearbook;
1991:788-792.
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