A 55-year-old man presents with slowly progressive, painless unilateral proptosis over 5 years. CT orbit shows a well-defined, encapsulated intraconal lesion with smooth margins, isodense to muscle, which appears to mould around the optic nerve without invading it. The most likely diagnosis is:

• A Orbital lymphoma
• B Optic nerve sheath meningioma
• C Rhabdomyosarcoma
• D Cavernous haemangioma (venous malformation) of the orbit ✓

Explanation

Cavernous haemangioma (now classified as venous malformation) is the most common benign intraconal orbital tumour in adults, presenting with slowly progressive painless proptosis. CT shows a well-encapsulated, round or oval, homogeneous, hyperdense lesion that enhances progressively on contrast administration ('progressive patchy enhancement' on dynamic MRI). It characteristically molds around the optic nerve without invading it. Orbital lymphoma also presents with moulding lesions but has a 'salmon patch' subconjunctival appearance and involves extraconal space. Optic nerve sheath meningioma causes a 'tram-track' sign on CT from calcification along the sheath. Rhabdomyosarcoma is the most common orbital malignancy in children, not middle-aged adults, and is rapidly progressive.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.