Idiopathic Orbital Inflammatory Syndrome (Orbital Pseudotumor)

Findings:

Multiple contrast enhanced orbital CT images demonstrate asymmetric thickening and increased enhancement of the right lateral and inferior rectus muscles, which extends to the tendinous attachment on the globe. There is subtle hazy stranding within the right intraconal orbital fat.

DIfferential Diagnosis:

orbital pseudotumor, Graves disease (not typical EOM involvement for this), lymphoma, sarcoidosis.

Discussion:

Orbital Pseudotumor (AKA Idiopathic Orbital Inflammatory Syndrome)
-idiopathic nongranulomatous inflammatory disorder
-third most common orbital disease (5%)
-children 15% of all cases
-acute onset with pain, swelling, erythema, ptosis, painful/restricted eye movement
-acute form usually responds to steroids
-uncommonly chronic with diplopia, proptosis
-chronic less commonly responds to steroids- XRT or chemo may help
-involves lacrimal gland, EOMs, fat
-orbital apex, cavernous sinus= Tolosa Hunt- painful ophthalmoplegia
-other systemic diseases associated:
-Wegener's, PAN, RP fibrosis, PSC, Reidel's, SLE, RA, dermatomyositis

Imaging:
-tendons involved and unilateral (to distinguish from Graves)
-marked enhancement
-retrobulbar fat stranding
-may present as focal or infiltrating mass
-rare bone destruction
-T2 hypointensity to distinguish from mets

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