<prompt> A patient with history of running nose and pain over medial aspect of the eye presents with sudden onset of high grade fever, prostration, chemosis, proptosis and diplopia on lateral gaze with congestion of the optic disc. Which of the following is the most likely diagnosis?Acute ethmoidal sinusitisOrbital cellulitisCavernous sinus thrombosisOrbital apex syndrome  <response>: Ans. c Cavernous sinus thrombosisRef: Parsons 20e, p. 456 - 459.Orbital apex syndrome and orbital cellulitis MC cause- ethmoidal sinusitis, present with concurrent complete external ophthalmoplegic. 