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Orbital Idiopathic Inflammatory Pseudotumor


KEY FACTS

Terminology

  • Nonspecific orbital inflammation, not due to any known etiology or systemic illness

Imaging

  • Best imaging tool: Contrast-enhanced MR with fat suppression

  • Poorly marginated mass-like enhancing soft tissue involving any area of orbit

  • Categorized by area(s) of involvement

    • Myositic, lacrimal, anterior, diffuse, apical

  • Moderate diffuse enlargement, irregularity, and enhancement of involved structures

  • Isointense or slightly hyperintense on T2WI or STIR

    • ↓ signal compared with many orbital lesions due to cellular infiltrate and fibrosis

    • ↓ signal in chronic disease suggests sclerosing variant and portends worse prognosis

Top Differential Diagnoses

  • Lymphoproliferative lesions

  • IgG4-related disease

  • Thyroid ophthalmopathy

  • Sarcoidosis

  • Wegener granulomatosis

  • Orbital cellulitis

Pathology

  • Polymorphous chronic inflammation and fibrosis

Clinical Issues

  • Symptoms: Pain and swelling, restricted eye motion, diplopia, proptosis, and impaired vision

  • 3rd most common orbital disorder

  • Steroid treatment effective in most patients

Diagnostic Checklist

  • Pseudotumor is diagnosis of exclusion

Axial graphic depicts multifocal orbital idiopathic inflammation, including involvement of the extraocular muscles
, orbital fat
, lacrimal gland
, sclera
, and optic sheath
.

Coronal T1WI C+ FS MR demonstrates extensive orbital inflammation, with ill-defined enlargement and enhancement of the rectus muscles
, extraconal infiltration extending to the lacrimal gland
, and intraconal enhancement partially surrounding the optic nerve
.

Coronal NECT in a middle-aged woman with left eye pain and diplopia shows enlargement and mild hypodensity of the left lateral rectus
. Isolated lateral rectus myositis is a typical manifestation of orbital pseudotumor, rare in thyroid orbitopathy.

Axial T1WI C+ FS MR in a patient with symptoms of uveitis shows orbital inflammatory changes of the anterior right orbit. Marked right uveoscleral “shaggy” enhancement is evident
, as well as ill-defined enhancement of the retrobulbar fat
.

TERMINOLOGY

Synonyms

  • Orbital pseudotumor (or simply “pseudotumor”)

Definitions

  • Pseudotumor = nonspecific orbital inflammation

  • Tolosa-Hunt

    • Variant form extending into cavernous sinus

  • Sclerosing orbital inflammatory pseudotumor

    • Variant characterized by chronic progressive fibrosis

IMAGING

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