Paralysisof 3rd, 4th, 6th nerves with involvement of ophthalmicdivisionof5thnerve, localizes the lesion to: (A) Apex of orbit, (B) Brainstem, (C) Cavernous sinus, (D) Base of skull
Answer is C. Ipsilateral ophthalmoplegia  causing diplopia occur due to 3rd, 4th  & 6th cranial nerves.
6th nerve passes through cavernous sinus and others are related to the lateral wall of cavernous sinuses.