====== Brain abscess etiology ======

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In [[1918]], Warrington investigated the etiological factors of [[brain abscess]] in 2 groups: 1) infections from foci in the contiguous structures; 2) infections spread through the bloodstream from a distant site
((W. B. Warrington; Critical Review: Abscess of the Brain, QJM: An International Journal of Medicine, Volume os-11, Issue 42, 1 January 1918, Pages 141–164, https://doi.org/10.1093/qjmed/os-11.42.141)).

These infections may result from contiguous spread of infection, hematogenous dissemination of bacteria, previous head trauma or neurosurgical procedure, or immunosuppression.
Brain abscess commonly occurs secondary to an adjacent infection (mostly in the middle ear or paranasal sinuses) or due to hematogenous spread from a distant infection or trauma. 

Historically direct extension from sinus or scalp infections was the most common source. More recently hematological spread has become most common. Direct introduction by trauma or surgery accounts for only a small minority of cases.



Its important to consider [[pulmonary arteriovenous malformation]] as an etiology of cerebral abscess when routine investigations fail to detect a source
((Nam TK, Park YS, Kwon JT. Brain Abscesses Associated with Asymptomatic
Pulmonary Arteriovenous Fistulas. J Korean Neurosurg Soc. 2017 Jan
1;60(1):118-124. doi: 10.3340/jkns.2015.0707.023. PubMed PMID: 28061502.
)).
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Development of brain [[abscess]] after an [[infarction]] is a rare clinical condition. There have been 11 cases in the literature. Many patients were treated with potent [[antibiotic]]s only and did not survive. Wang et al., present 2 cases in which patients received aggressive surgical resection of brain abscess and survived. The analysis of the literature confirmed this finding that surgical intervention of brain abscess in patients after [[stroke]] is advisable.

Secondary abscess formation after significant [[ischemic stroke]] is a rare condition that carries potential for high [[morbidity]]/[[mortality]]. The limited body of [[literature]] with the addition of our 2 cases supports aggressive management with surgical evacuation of brain abscess to increase survival.
((Wang J, Fraser JF. An Intracranial Petri Dish? Formation of Abscess in Prior
Large Stroke After Decompressive Hemicraniectomy. World Neurosurg. 2015
Nov;84(5):1495.e5-9. doi: 10.1016/j.wneu.2015.05.013. PubMed PMID: 25988538.
)).

===== Organisms =====
[[Streptococcus]] is most common, up to 60 % are polymicrobial.

see [[Staphylococcus aureus brain abscess]]
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 Streptococcus pneumoniae accounts for <1% of pyogenic [[brain abscess]]es
((Dakkak M, Cullinane WR Jr, Ramoutar VR. Subdural Empyema Complicating
Bacterial Meningitis: A Challenging Diagnosis in a Patient with Polysubstance
Abuse. Case Rep Med. 2015;2015:931819. doi: 10.1155/2015/931819. Epub 2015 Oct
12. PubMed PMID: 26543484; PubMed Central PMCID: PMC4620381.
)).



===== Risk Factors =====
[[TNFα]] (-308 G>A) and IL-1β (-511 C<T) polymorphisms that lead to increased production of TNF-α and IL-1β appear to be risk for development of brain abscess in North Indian population
((Mishra P, Prasad KN, Singh K, Bajpai A, Sahu RN, Ojha BK. Tumor necrosis
factor-α and interleukin-1β gene polymorphisms and risk of brain abscess in North
Indian population. Cytokine. 2015 Sep;75(1):159-64. doi:
10.1016/j.cyto.2015.07.009. Epub 2015 Jul 14. PubMed PMID: 26187330.)).
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Until recently, post-radiotherapy brain abscess was considered rare, but it has become an increasingly important etiology. Discussions of the relationship between bacterial brain abscess and radiotherapy (RT) are rare in the literature. Further study based on a proper patient cohort is warranted
((Chuang JM, Lin WC, Fang FM, Huang YJ, Ho JT, Lu CH. Bacterial brain abscess
formation in post-irradiated patients: What is the possible pathogenesis? Clin
Neurol Neurosurg. 2015 Sep;136:132-8. doi: 10.1016/j.clineuro.2015.05.025. Epub
2015 Jun 9. PubMed PMID: 26099700.
)).

[[AIDS]]

[[Chalazion]]

[[Chronic sinusitis]]

[[Chronic otitis]]

[[Congenital cyanotic heart disease]]

[[Infective endocarditis]]

[[Immunodeficiency]]

[[Dental procedures]], [[streptococcus]] oral flora is frequent

[[Penetrating head injury]].


===Pulmonary abnormalities===

[[Lung abscess]]

[[Pulmonary arteriovenous malformation]]: 50 % have [[Osler-Weber-Rendu syndrome]].

[[Lung empyema]].

===Intracerebral haemorrhage===
see [[Brain abscess after intracerebral hemorrhage]].


===== Spread =====
Prior to 1980 brain [[abscess]]es classically result from [[contiguous spread]] (extension of nearby [[infection]] in the [[head]], [[penetrating head injury]], neurosurgery),[[direct trauma]]. 

Now [[hematogenous spread]] is the most common vector.

However, up to 30% of brain abscesses have no such associations and thus are deemed [[cryptogenic brain abscess]]
((Mathisen GE, Johnson JP. Brain abscess. Clin Infect Dis 1997;25:763-779; quiz 780-781.)).

Generally occurring after septic episodes in immunodeficient patients or complicating neurosurgical procedures. Even though they are known complications of surgically treated intracerebral haemorrhages (ICH), the presence of a brain abscess at the site of an untreated ICH is a rare event.

Such cases may result from haematogenous spread from distant foci or contiguous sites and are often preceded by episodes of sepsis and local infection. Immunodeficiency, AIDS, age, diabetes mellitus and vitamin-K deficiency are predisposing factors. 

===== Vectors =====

===Hematogenous spread===
Multiple abscesses have been noted in 10 to 50% of these patients
((Mamelak AN, Mampalam TJ, Obana WG, Rosenblum ML. Improved management of
multiple brain abscesses: a combined surgical and medical approach. Neurosurgery.
1995 Jan;36(1):76-85; discussion 85-6. PubMed PMID: 7708172.)). 

The chest is the most common origin, from a remote infectious source through right-to-left shunting
((Kawamata T, Takeshita M, Ishizuka N, Hori T. Patent foramen ovale
as a possible risk factor for cryptogenic brain abscess: report of two
cases. Neurosurgery 2001;49:204-206; discussion 206-207.)).
[[Lung abscess]] the most common

In patients with [[bronchiectasis]] and with new neurological manifestations, infected lesions in the central nervous system should be excluded.

In [[child]]ren [[congenital cyanotic heart disease]], especially [[tetralogy of Fallot]].

[[Right to left shunting]] ([[Pulmonary arteriovenous malformation]]).

[[Osler-Weber-Rendu syndrome]]

Bacterial [[endocarditis]]

[[Dental abscess]]

Infections of the abdomen – such as peritonitis (an infection of the bowel lining).

Pelvic infections – such as infection of the bladder lining (cystitis).

[[Septic embolism]] in areas of previous brain [[infarction]] or [[ischemia]].

===Fibrosis lung disease===
Is an uncommon complication of severe [[cystic fibrosis]] lung disease
((Fenton ME, Cockcroft DW, Gjevre JA. Intracerebral abscess: a complication of
severe cystic fibrosis lung disease. Can Respir J. 2008 Jan-Feb;15(1):45-7.
PubMed PMID: 18292854; PubMed Central PMCID: PMC2677856.)).

===Contiguous spread===

===Purulent sinusitis===
[[Osteomyelitis]] or [[phlebitis]] of [[emissary vein]]s.

[[Otitis media]].

===== Brain abscess from odontogenic infection =====

[[Brain abscess from odontogenic infection]].

===== Brain Abscess Following Cerebrospinal Fluid Fistula =====

[[Brain Abscess Following Cerebrospinal Fluid Fistula]].