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Idiopathic orbital inflammation (IOI), also known as orbital pseudotumor, is a non-infectious, non-neoplastic inflammatory condition of the orbit of unknown etiology, typically presenting acutely or subacutely with painful orbital signs. It is a diagnosis of exclusion.
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| Feature | Details |
|---|---|
| Etiology | Unknown; likely autoimmune or post-infectious |
| Triggers | May follow viral illness, trauma, or surgery |
| Pathology | Non-granulomatous, polymorphous inflammatory infiltrate with variable fibrosis |
| Target tissues | Can affect extraocular muscles, lacrimal gland, optic nerve sheath, sclera, orbital fat, or diffuse orbit |
| Feature | Description |
|---|---|
| Age | Can occur at any age, but most common in adults (30–50 years) |
| Sex | Slight female predominance |
| Laterality | Typically unilateral (bilateral in ~10–15%, often in children) |
Symptoms are painful, acute/subacute, and often self-limited or steroid-responsive
| Symptom | Description |
|---|---|
| Acute orbital pain | Hallmark symptom; distinguishes from many other orbital pathologies |
| Proptosis | Common in anterior IOI or muscle involvement |
| EOM restriction & diplopia | Painful limitation of eye movements |
| Periorbital edema & erythema | Often present with chemosis |
| Lacrimal gland enlargement | In dacryoadenitis form |
| Vision loss | If optic nerve or posterior orbit involved |
General features:
| Modality | Findings |
|---|---|
| CT | • Diffuse or focal orbital soft tissue thickening |
| • Stranding of orbital fat | |
| • Involvement of EOM including tendinous insertions (vs sparing in thyroid orbitopathy) | |
| • ± bony remodeling or sclerosis (chronic cases) | |
| MR | • T1: Isointense to muscle |
| • T2: Variable; hyperintense in active inflammation, hypointense in fibrosis | |
| • Post-contrast: Intense, diffuse enhancement | |
| • May involve optic nerve sheath, sclera, tenon’s capsule, or superior orbital fissure |
Orbital pseudotumor in a 7-month-old male with a 3-month history of right eye swelling. a Coronal contrast-enhanced CT image shows an enhancing periocular soft-tissue mass (small black arrow) along the superior and lateral aspect of the globe with inferior displacement of the globe and lateral extension into the periorbital soft tissue (open arrow). b Coronal contrast-enhanced fat-suppressed T1 MR image shows an enhancing periocular soft-tissue mass (small black arrow) along the superior and lateral aspect of the globe with inferior displacement of the globe and lateral extension into the periorbital soft tissue (open arrow)
Gerrie, S.K., Rajani, H., Navarro, O.M. et al. Pediatric orbital lesions: non-neoplastic extraocular soft-tissue lesions. Pediatr Radiol 54, 910–921 (2024). https://doi.org/10.1007/s00247-024-05892-x
Subtypes of IOI:
| Subtype | Key Features |
|---|---|
| Myositis | Involves one or more EOMs, including tendinous insertions; most common subtype |
| Dacryoadenitis | Involves lacrimal gland; S-shaped ptosis, upper eyelid swelling |
| Orbital apex syndrome | Involves optic nerve, superior orbital fissure, ± cranial nerves II, III, IV, V1, VI |
| Diffuse IOI | Involves multiple compartments, including fat and sclera |
| Perineuritis | Enhancing thickened optic nerve sheath (can mimic optic neuritis) |
Idiopathic orbital inflammation in the typical group top: orbital myositis in the typical group. CT scan coronal view (left) shows lateral rectus muscle enlargement in the left eye and adjacent fuzzy shadows (arrowhead) and fat-suppressed T2-weighted MRI a coronal view (right) shows high signal intensity of lateral rectus muscle fascia in the left eye. Bottom: diffuse type adjacent lesion around the eye.
Toshinobu Kubota, Akari Iwakoshi - Clinical heterogeneity between two subgroups of patients with idiopathic orbital inflammation: BMJ Open Ophthalmology 2022;7:e001005.