What does interval opacification of the sphenoid sinus mean? differences between the different sinuses?

Inflammation/infctn: It means compared to the prior images (i'm assuming you had a sinus ct done) there seems to be some fluid or discharge in the sphenoid sinuses which is one of the inner most sinuses, more inside of the brain. If infected severely, the infection could spread to the brain.Infection is less common, more in the frontal and maxillary sinuses. Opacfication might mean discharge from allergies as well.

Mucous: Basically when the sinus is opacified, it means that there is mucous or some sort of inflammation of the lining of the sinus. There are various sinuses: maxillary, sphenoid. What differentiates the sinuses is location. For instance maxillary is under your cheek bones. Try cleaning up your diet of starches and sugar, eat more greens and it may all clear up without antibiotics. Hope this helps!