THe answer to this question would be: Cribriform plate
The ethmoid bone is divided into three major area: cribriform plate, perpendicular plate, and labyrinth. Cribriform plate is the one that separates the skull with the nasal cavity. If it is damaged, the sterile area of the brain might be exposed to the nasal cavity which has a flora of microbes. It will provide a route for the bacteria to infect the brain.