Nasal cause of sixth cranial nerve palsy.

Anatomically the cavernous sinus is closely related to the sphenoid sinus and the nasopharynx. Sphenoid sinusitis, as demonstrated in the case can affect the nerves which are contained within it. Apart from the sinus, a direct extension from a nasopharyngeal lesion is commonly encountered to cause diplopia, owing to the sixth nerve involvement. The provisional diagnosis should be a nasopharyngeal carcinoma (NPC).