This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
19 year old young girl with previous history of repeated pain over medial canthus and chronic use of nasal decongestants, presented with abrupt onset of fever with chills & rigor, diplopia on lateral gaze,moderate proptosis & chemosis. On examination optic disc is congested. Most likely diagnosis is 
Select and explain. 
A. Cavernous sinus thrombosis, B. Orbital cellulitis, C. Acute Ethmoidal sinusitis, D. Orbital apex syndrome
A: Cavernous sinus thrombosis
Answer: A: Cavernous sinus thrombosis 
Explanation: It Stas initially as a unilateral condition which soon becomes bilateral due to intercavernous connection. It should be differentiated from orbital cellulitis and panophthalmitis. Ref: ak khurana 6th edition pg no412