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 1).
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 2).
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 antibiotics 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. 3).
Streptococcus is most common, up to 60 % are polymicrobial.
see Staphylococcus aureus brain abscess
Streptococcus pneumoniae accounts for <1% of pyogenic brain abscesses 4).
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 5).
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 6).
Congenital cyanotic heart disease
Dental procedures, streptococcus oral flora is frequent
Prior to 1980 brain abscesses 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 7).
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.
Multiple abscesses have been noted in 10 to 50% of these patients 8).
The chest is the most common origin, from a remote infectious source through right-to-left shunting 9). 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 children congenital cyanotic heart disease, especially tetralogy of Fallot.
Right to left shunting (Pulmonary arteriovenous malformation).
Bacterial endocarditis
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.
Is an uncommon complication of severe cystic fibrosis lung disease 10).
Osteomyelitis or phlebitis of emissary veins.