A 55-year-old woman has bilateral proptosis with enlargement of the inferior and medial recti on CT, but the muscle bellies are enlarged while their tendinous insertions are characteristically spared. Which differential diagnosis does this tendinous sparing help to EXCLUDE?
- A Metastatic breast carcinoma to the orbit
- B Carotid-cavernous fistula
- C Idiopathic orbital inflammatory disease (orbital pseudotumor) ✓
- D Orbital amyloidosis
Correct answer: C. Idiopathic orbital inflammatory disease (orbital pseudotumor)
Explanation
In thyroid eye disease the extraocular muscles are enlarged in their bellies with sparing of the tendons, whereas idiopathic orbital inflammation involves both the belly and the tendon, producing a thickened insertion on imaging. This distinction is a classic discriminator between the two commonest causes of extraocular muscle enlargement. Carotid-cavernous fistula and metastases do not produce this specific pattern of isolated muscle enlargement.
Reference: Yanoff and Duker Ophthalmology, 5th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.