I'd go for a second opinion. Sinus sounds off to me.
When I was around 16, I had a hole in my shoulder in the area of my bra strap. It was painful but nothing came out of it. My mother per doctors instruction, put a black medicine on it to draw out whatever was in it which I assume was pus. Once it was all out the pain was gone and it healed but I had a scar for years. I was told it was an inverted boil which probably has a medical term. This never happened again, however I have had boils at an older age on different part of the body.
Good Luck.
My sister in law had the same sort of thing only it was on the back of her leg. Hers was leaking fluid and blood and it was painful too. Hers also had a bad smell to the fluid that came out. Does your wifes? Anyhow hers got bigger, turned hard in the center, and black around the outsides. It started to look like a boil.
She went to the doctor and they didnt know what it was at first, so they took a bit of the skin around it for testing. It came back as MRSA staph infection. I guess they found it in time to take antibiotics, otherwise she would have had to been hospitalized. Staph infection is going around for some reason here lately, so like graveslady said, I would also get a second opinion if I were you. Keep us updated!