<prompt> Unilateral proptosis bilateral 6th nerve palsy is seen in -Cavernous sinus thrombosisMeningitisHydrocephalusNone  <response>: Cavernous sinus thrombosisThe cavernous sinus is a cavity at the base of the brain that contains a vein, several nerves, and other structures.The vein and cavity run between the large bone at the base of the skull sphenoid bone and temporal bone near the temple, therefore infection to cavernous sinus can spread from the sinuses, teeth, ears, eyes, noses or skin of the face. Routes of spread includei. Ethmoid sinus most common via ophthalmic veinsii. Sphenoid sinus by direct spreadiii. Frontal sinus via supraorbital and ophthalmic veinsiv. Orbit by ophthalmic veinsv. Upper lid via Angular vein and ophthalmic veinsvi. Ear by petrosal venous sinuses Clinical features of cavernous sinus thrombosisOnset is abrupt with chills and rigor It is bilateralInvolvement of III rd, IV th, V th and VI th cranial nerveChemosis of conjunctivaProptosis of the eye with limited movementsPapilloedemaPupils are dilated and fixedDecreased visionDecreased sensation in distribution of Vth nerve ophthalmic divisionProgressive ophthalmoplegia specially for lateral gaze 