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 man following RTA presented with proptosis and pain in the right eye after four days. On examination, there is a bruise on the forehead and right eye. What is the diagnosis - 
Select and explain. 
A. Cavernous sinus thrombosis, B. Internal carotid artery aneurysm, C. Carotico-cavernous fistula, D. Fracture of sphenoid
C: Carotico-cavernous fistula
Answer: C: Carotico-cavernous fistula 
Explanation: Common causes of proptosis associated with craniofacial trauma are:-

1) Carotid-cavernous fistula
ii) Retrobulbar hematoma
iii) Superior orbital fissure and orbital apex syndrome

Rare causes are:-


Cavernous sinus thrombosis
Subperiosteal hematoma


So, amongst the given options carotico-cavernous fistula is the only common cause.
Cavernous sinus thrombosis may also occur after trauma. But, trauma is a very rare cause of CST. It usually develops as complication of extension of infection from the adjacent sinus, teeth, ear, nose etc.