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Idiopathic orbital pseudotumor


Key points

  • Definition: Idiopathic orbital pseudotumor (IOP) is a nonmalignant, nongranulomatous extraocular orbital and adnexal space-occupying lesion simulating neoplasm without associated local or systemic etiology.

  • Synonyms: Idiopathic orbital inflammation (IOI), idiopathic orbital inflammatory disease, nonspecific orbital inflammation (NSOI).

  • Classic clue: 45-year-old female presents with pain, proptosis, periorbital swelling, and decreased vision in one or both eyes. Imaging shows poorly circumscribed enhancing intraorbital soft tissue mass.

  • Most common cause of painful orbital mass in adults.

  • Associated with proptosis, retinal detachment, uveitis, and Tolosa-Hunt syndrome with cranial nerve palsy.

  • It is a diagnosis of exclusion. It is necessary to rule out neoplasm, primary infection, and systemic disorders.

Imaging

General imaging features

  • Imaging findings are characterized by inflammatory changes in orbital structures, including globe, lacrimal glands, extraorbital muscles (EOMs), orbital fat, and optic nerve (ON).

Computed tomography features

  • Computed tomography (CT) can reveal abnormal enhancement of retrobulbar fat, which sometimes occurs.

  • May see lacrimal, EOM, or other intraorbital mass.

  • May be focal or infiltrative.

  • Lesions are poorly circumscribed.

  • Dynamic CT shows late phase increased attenuation increasing (contrary to lymphoma, which shows decreased late phase attenuation).

  • May show bone remodeling or erosion.

  • May see nonspecific structural thickening of sclera, episclera, Tenon’s capsule, and uvea.

  • Can cause diffuse infiltration of orbital fat, globe, and ON sheath complex.

  • See General Imaging Features earlier.

Magnetic resonance imaging features

  • Magnetic resonance imaging (MRI) with Gd and fat suppression is the modality of choice.

  • T1 hypointense to orbital fat on T1 (see Figure 36-2 , A ).

    FIGURE 36-2 ■, A, Axial T1 shows abnormal soft tissue sharply hypointense to orbital fat enlarging the left lateral rectus muscle and replacing retroorbital fat with exophthalmos. B, Axial T2 shows low attenuation of soft tissue mass causing exophthalmos, ON displacement, and obliteration of CSF along mid and posterior ON sheath. C, Axial T1 + Gd shows avid abnormal enhancement of the left lateral rectus muscle, retrobulbar fat, orbital apex, and cavernous sinus.

  • T2 isointense or slightly hyperintense compared to muscle (see Figure 36-2 , B ).

  • T1 + Gd shows marginal irregularity with avid enhancement (see Figure 36-2 , C ).

  • Short tau inversion recovery (STIR) findings are similar to T2 fat-saturation (fat-sat).

  • In Tolosa-Hunt syndrome (THS), enhancement and fullness of anterior cavernous sinus and superior orbital fissure (SOF) on T1 + Gd.

  • In THS, magnetic resonance angiography (MRA) may show narrowing of cavernous internal carotid artery (ICA).

Clinical issues

Presentation

  • Presenting problems include pain, proptosis, periorbital swelling, decreased visual acuity, and decreased motility. ,

  • Typically acute, occasionally insidious.

  • Usually unilateral.

Epidemiology

  • IOP is the second most common cause of exophthalmos following Graves orbitopathy (GO).

  • IOP is the third most common orbital disorder following GO and lymphoma.

  • The mean age at presentation for IOP is 45 years.

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