This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
[{'content': 'A 20 year old patient presented with unilateral proptosis which was compressible and increases on bending forward. No thrill or bruit was present. MRI shows a retro-orbital mass with enhancement Diagnosis is \nSelect and explain. \nA. AV malformations, B. Orbital encephalocele, C. Orbital Varix, D. Neurofibromatosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]