Editing Brain abscess (section)

===Bacterial===
[[File:Brain MRI 131749 rgbca-.png|thumb|Brain abscess after metastasis treatment.]]
Anaerobic and microaerophilic cocci and gram-negative and gram-positive [[anaerobic infection|anaerobic]] bacilli are the predominant bacterial [[Isolation (microbiology)|isolate]]s. Many brain abscesses are polymicrobial. The predominant organisms include: ''[[Staphylococcus aureus]]'', aerobic and anaerobic streptococci (especially ''[[Streptococcus intermedius]]''), ''[[Bacteroides]]'', ''[[Prevotella]]'', and ''[[Fusobacterium]]'' species, Enterobacteriaceae, ''[[Pseudomonas]]'' species, and other anaerobes.<ref>{{cite journal | vauthors = Brook I | title = Microbiology and antimicrobial treatment of orbital and intracranial complications of sinusitis in children and their management | journal = International Journal of Pediatric Otorhinolaryngology | volume = 73 | issue = 9 | pages = 1183–1186 | date = September 2009 | pmid = 19249108 | doi = 10.1016/j.ijporl.2009.01.020 }}</ref> Less common organisms include: ''Haemophillus influenzae'', ''Streptococcus pneumoniae'' and ''Neisseria meningitidis''.<ref>{{cite journal | vauthors = Brook I | title = Brain abscess in children: microbiology and management | journal = Journal of Child Neurology | volume = 10 | issue = 4 | pages = 283–288 | date = July 1995 | pmid = 7594262 | doi = 10.1177/088307389501000405 | s2cid = 72747359 }}</ref>

Bacterial abscesses rarely (if ever) arise ''de novo'' within the brain although establishing a cause can be difficult in many cases.  There is almost always a primary lesion elsewhere in the body that must be sought assiduously because failure to treat the primary lesion will result in relapse.  In cases of trauma, for example in compound skull fractures where fragments of bone are pushed into the substance of the brain, the cause of the abscess is obvious.  Similarly, bullets and other foreign bodies may become sources of infection if left in place.  The location of the primary lesion may be suggested by the location of the abscess: infections of the middle ear result in lesions in the [[middle cranial fossa|middle]] and [[posterior cranial fossa|posterior]] cranial fossae;<ref>{{cite book | author=Macewan W | year=1893 | title=Pyogenic Infective Diseases of the Brain and Spinal Cord | location=Glasgow | publisher=James Maclehose and Sons }}</ref> congenital heart disease with right-to-left shunts often result in abscesses in the distribution of the [[middle cerebral artery]];<ref>{{cite book |vauthors=Ingraham FD, Matson DD | title=Neurosurgery of Infancy andChildhood | location=Springfield, Ill | publisher=Charles C Thomas | year=1954 | pages=377 }}</ref><ref>{{cite journal | vauthors = Raimondi AJ, Matsumoto S, Miller RA | title = Brain abscess in children with congenital heart disease. I | journal = Journal of Neurosurgery | volume = 23 | issue = 6 | pages = 588–595 | date = December 1965 | pmid = 5861142 | doi = 10.3171/jns.1965.23.6.0588 | s2cid = 22383252 }}</ref> and infection of the [[frontal sinus|frontal]] and [[ethmoid sinus|ethmoid]] sinuses usually results in collection in the subdural sinuses.{{cn|date=June 2022}}