Unilateral proptosis & bilateral 6th nerve palsy is seen in -

Cavernous sinus thrombosis The 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 include i. Ethmoid sinus (most common) via ophthalmic veins ii. Sphenoid sinus by direct spread iii. Frontal sinus via supraorbital and ophthalmic veins iv. Orbit by ophthalmic veins v. Upper lid via Angular vein and ophthalmic veins vi. Ear by petrosal venous sinuses Clinical features of cavernous sinus thrombosis Onset is abrupt with chills and rigor It is bilateral Involvement of III rd, IV th, V th and VI th cranial nerve Chemosis of conjunctiva Proptosis of the eye with limited movements Papilloedema Pupils are dilated and fixed Decreased vision Decreased sensation in distribution of Vth nerve (ophthalmic division) Progressive ophthalmoplegia (specially for lateral gaze)