I had sphenoid fungus and did surgery last nov.2013 to clean it ,the culture test confirmed that it is fungus ball non invasive. now it come back. why?

Depends: It depends on why you contracted the fungal ball in the first place. Abnormalities in your immune system or the architecture of your nares may predispose you to getting this infection. Ask your doctor why it happened a second time.

Recurrence: A fungal infection like that is potentially very serious, as you may well know. Most likely it recurred because the same conditions that caused it in the first place have recurred or weren't completely treated with the surgery. You must see your surgeon ASAP. Prompt treatment may prevent need for more surgery. Also, the underlying cause (allergies. polyps) needs to be addressed.

Sinus infection: Fungus infections of the sinuses can be difficult to eradicate with or without surgery. Often a second operation is required to eliminate the infection. Sometimes the fungus infection is caused by an allergy or a low immune system. It is important to treat the infection aggressively because the fungus can spread to the eyes or the brain and cause serious neurological damage .