Place the lesion in its compartment (globe, optic nerve sheath, intraconal, extraconal, lacrimal gland), then its behaviour: cavernous venous malformation, schwannoma, lymphoma, optic nerve glioma or meningioma, lacrimal tumours and metastases each have a home.
Orient first
- Intraconal: cavernous venous malformation (commonest in adults), schwannoma; optic nerve sheath: meningioma (tram-track), glioma (fusiform, NF1).
- Extraconal: lymphoma (moulds to the globe), dermoid (fat), lacrimal gland tumours (superolateral).
- Idiopathic orbital inflammation and IgG4-related disease mimic tumour.
Acquire the study
- T1, fat-saturated T2, DWI, dynamic and delayed post-gadolinium fat-saturated T1.
The manoeuvre
- Compartment on coronal T1: relation to the muscle cone and optic nerve.
- Dynamic post-contrast: patchy early enhancement filling in progressively = cavernous venous malformation.
- DWI: low ADC in lymphoma.
- Optic nerve sheath: tram-track enhancement (meningioma) vs enlarged nerve (glioma).
What confirms it
- Compartment and imaging pattern concordant with a named entity; biopsy when not diagnostic.
What licenses you to exclude it
- Normal orbit on MRI excludes a mass as the cause of proptosis.
The classic misread
- Fat-saturation failure at the orbital apex mimicking enhancement.