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
A young adult presents with proptosis and pain in eye after 4 days of trauma to eye. Chemosis, conjunctival congestion and extraocular muscle palsy with inability to move eye are seen.Investigation of choice - 
Select and explain. 
A. MRI, B. Digital subtraction angiography, C. CT, D. MR angiography
B: Digital subtraction angiography
Answer: B: Digital subtraction angiography 
Explanation: Information in this question are :-


Presentation 4 days after trauma
Traumatic proptosis along with chemosis and conjunctival congestion
Extraocular muscle palsy (ophthalmoplegia)


Given the patient's clinical presentation of proptosis with chemosis and conjunctival congestion in the setting of cranio-facial injury, a traumatic carotid-cavernous fistula is suspected.
Most likely diagnosis is carotico-cavernous fistula.
Selective carotid angiography using digital subtraction techniques is the investigation of choice.
Another condition which may present with similar features is CST, but it is very rare after trauma.