Orbital inflammatory syndrome (OIS), also known as orbital pseudotumor, is a diagnosis of exclusion when evaluating proptosis. The typical presentation is unilateral, painful proptosis. It is categorized based on region of involvement in the orbit as either diffuse, anterior, lacrimal, myositic, and apical.
On CECT an enhancing orbital mass is seen. The mass is hypointense on T1WI and iso- to hyperintense on T2WI. Irregular contrast enhancement is seen with gadolinium.
The above image demonstrates an enhancing left orbital apical pseudotumor causing proptosis. This should be differentiated from the imaging appearance of Graves Ophthalmopathy.
Chaudhry IA, Shamsi FA, Arat YO, et al. Orbital pseudotumor: distinct diagnostic features and management. Middle East Afr J Ophthalmol 2008; 15(1):17-27.
LeBedis CA, Sakai Osamu. Nontraumatic orbital conditions: diagnosis with CT and MR imaging in the emergent setting. Radiographics 2008;28:1741-53.