Intracranial infections are very unlikely to occur, first, the brain is the center of the human body, this center has a blood-brain barrier, this blood-brain barrier is quite a good defense measures, general bacteria, viruses are very unlikely to invade, under certain conditions, common blood-borne infections, blood-borne bacteria, viruses, mycoplasma or tuberculosis bacteria, through the blood, such as on the legs or lungs of these places where infections occur, bacterial Invasion, these bacteria with the blood circulation into the brain, usually does not appear, under certain conditions may appear, especially children blood-brain barrier is not particularly good, may be high incidence of higher chances, the proportion of the first incidence of higher, this is the blood-borne transmission. Secondly, it is the neighboring organs, such as the nasal cavity, the tissues near the brain appear to be infected, the neighboring ones are also easy to invade the brain, like otitis media, sinusitis. Third, under normal circumstances the brain is very solid, is very airtight organ, if encountered in a car accident or trauma, cranial brain cracked a slit, traumatic cranial bone fragments of the embedded, knife, sharp instrument pierced into the brain foreign things or more or less will carry pathogenic bacteria, will also cause intracranial infections, these are the three common causes.