Orbital pseudotumour

Dr Varun Babu and A.Prof Frank Gaillard et al.

Orbital pseudotumour is an idiopathic inflammatory condition that most commonly involves the extraocular muscles. Less commonly there is inflammatory change involving the uvea, sclera, lacrimal gland, and retrobulbar soft tissues. The exact aetiology is not known but an association with many inflammatory/autoimmune diseases is reported.

Patients typically present with rapid-onset, usually unilateral (~90% of cases), painful proptosis and diplopia

Histologically acute lesions demonstrate lymphocyte (which can be mistaken for orbital lymphoma), plasma cell, and giant cell infiltration.

Division into a number of subgroups according to location has been proposed:

  1. lacrimal pseudotumour
  2. anterior pseudotumour: immediately behind the globe
  3. posterior pseudotumour: distinguished from Tolosa-Hunt syndrome in that the cavernous sinus is spared
  4. diffuse pseudotumour
  5. myositic pseudotumour: predominantly involve the EOMs and therefore mimic thyroid associated orbitopathy (TAO) but unlike TAO it also involves the tendons 

The condition has been associated with many wider inflammatory and autoimmune conditions including:

Imaging demonstrates enlargement of the muscle belly of one (or more) extraocular muscles with involvement of their tendinous insertions. Involvement of the tendinous insertion distinguishes it from thyroid associated orbitopathy (TAO) in which the insertion point is spared. Additional inflammation can be seen in surrounding tissues, including the lacrimal gland. It can appear as an infiltrative mass and extends outside of the orbit via superior or inferior orbital fissures. Extension into the cavernous sinus, meninges, and dura can occur.

Reported signal characteristics include:

  • T1: affected region typically iso- 4 to hypointense 3
  • T2: affected region typically hypointense due to fibrosis and with more progression of fibrosis it becomes more hypointense 3
  • T1 C+ (Gd): diffuse enhancement 

Most cases resolve rapidly with treatment (usually steroids suffice) although in a subset with more chronic progression chemotherapy and radiotherapy may be required. A degree of residual fibrosis can be demonstrated, especially in the more refractory cases.

General imaging differential considerations include:

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Article information

rID: 1781
System: Head & Neck
Synonyms or Alternate Spellings:
  • Idiopathic orbital inflammatory disease
  • ISIO
  • Idiopathic Sclerotic Inflammation of the Orbit (ISIO)
  • OIS
  • Orbital inflammatory syndrome
  • Pseudotumour of orbit
  • Orbital pseudotumours
  • Orbital pseudotumors
  • Orbital pseudotumor
  • Inflammatory pseudotumor of the orbit
  • Orbital inflammatory pseudotumour

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