CBCT scan shows a void within the bone: what could it be?

Have you asked the patient if he or she has had a previous sinus augmentation? This looks like a previous graft with a void in it.

Appears they had sinus augmentation and the void is within that graft

T Carlos and Greg make a good point. Open it up, biopsy and or culture with stains. Renter after reports arrive and graft with a particulate after treating accordingly. Implant after the graft has turned over.

Doesn't look pathologic to me. If you can get primary stability, I don't see anything wrong with placing the implant. Or grafting the space.

There was an article years ago in JOMI I believe in which an author (can't cite it, sorry) presented several cases with such voids and considered them small zones of complicated healing, possibly from small infections in the graft. He began mixing metronidazole solution in his grafts after that and eliminated such voids. I've never been able to get Metronidazole in solution in expensively (you can get it in in 250 ml bags but you have to buy a bunch at once) so never tried it, but it seems rational judging from his results. I've noticed smaller such voids before occasionally and just implanted within. However, yours is quite large. Might want to enter, disinfect, and re-graft just to be sure it's not actively infected. Would hate to place the implant and then lose it after restoration. Good Luck

These voids in the bone are areas where the bone did not heal completely The upper third heals with normal Haversian bone while the apical third of the extraction socket is filled with a soft mushy content. These lesions can be very small and are inadvertantly treated at the time of implant placement and, if youare lucky the implant will integrate because you have "perturbed"the bone (caused bleeding in the bone which can now heal in a normal process of bone healing) Sometimes the void might be a bit bigger and the necrotic mush is not adequately removed and/or sufficient bleeding in the osteotomy site did not take place. These bony voids are a poorly recognized lesion of all marrow containing bone and have been termed FOMD (focal osteoporotic marrow defect) CAVITATIONS, NICOlesions etc. The presence of such a void must be considered when 1/the amount and quality of the bone is deficient at time implant placement 2/the patient experiences pain or discomfort when drilling the bone in spite of adequate local anaesthetic administration 3/the implant remains painful weeks after implant placement 4/ the imlant spontaneously "sheds" Bicon implants is about to publish a book on implantology and deals at some length with this very condition