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Salmonella spp . have rarely been reported to cause brain abscess, usually after bacteremia in the presence of
some compromise of the reticuloendothelial system [19]. Cereberal abscess may also be a complication of neurologic
infection with Burkholderiapseudomallei [20]. Actinomycosis of CNS may manifest brain abscess, usually secondary to hematogenous spread from a primary infection in the lung, abdomen, or pelvis, although contiguous spread from foci of infection in the ears, paranasalsinuses, orcervicofacial regions may occur [21].
Nocardial brain abscess is caused by Nocardia asteroids may occur as an isolated CNS lesion or as a
disseminated infection in association with pulmonary or cutaneous disease [21]. In a series of organ transplant recipients with Nocardia brain abscess, use of trimethoprim-sulfametoxazole prophylaxis for Pneumocysticjirovecii
(formerly P.carinii ) was not shown to be protective against No cardia infection [22].
Mycobacterium tuberculosis and nontuberculous my cobacteria have been increasingly observed to cause focal
CNS lesions, with several cases reported in patients with HIV infection [3, 23].
Fungal Brain Abscess
The incidence of fungal brain abscess has increased as a result of the prevalent administration of
immunosuppressive agents, broad- spectrum antimicrobial therapy and corticosteroids [24].
Candida spp
The diagnosis of fungal brain abscess id often unexpected and many cases are not discovered until autopsy.
In autopsy studies, Candida spp. have emerged as the most prevalent etiologic agents; neuropathological lesions include
micro abscesses, noncaseating granulomas, and diffuse glial nodules. Risk factors for invasive Candida infection include the use of corticosteroids, broad –spectrum antimicrobial therapy, and hyperalimentation.
Disease also seen in premature infants; in patients with malignancy, neutropenia, chronic granulomatous disease,
diabetesmellitus, or thermal injuries, and in patients with catheter in place [25].
Aspergillus spp
Intracranial seeding of Aspergillus species occurs during dissemination of the organism from the lungs or by
direct extension from a site anatomically adjacent to the brain [26]. Cases of intracranial infection caused by Aspergillus
spp. have been reported worldwide, with most cases occurring in adults. Cerebralaspergillosis is reported in 10% to 20% of all cases of invasive aspergillosis, and rarely is the brain the only site of infection [27].
Mucromycosis Mucromycosis is one of the most fulminant fungal infections known [26]. Many predisposing conditions to mucromycosis have been described, including diabetes mellitus,(70% of cases)usually in association with acidosis, acidemia from profound systemic illnesses (e.g. sepsis, severe dehydration, severe diarrhea, chronic renal failure [25].
Pseudallescheriaboydii
CNS disease may occur in both normal and immune compromised hosts. This organism is being increasingly
referred to as Scedos poriumapiospermum , the sexual form of P.boydii. The organism may enter the CNS by direct trauma,
by hematogenous dissemination from primary site of infection, via an intravenous catheter, or direct extension from
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infected sinuses [26].
Many etiologic agents of fungal meningitis may also cause brain abscess, e.g. Cryptococcus
neoformans, Coccidioidesspp, Histoplasmacapsulatum , and Blastmycesdermatiditis [25].
Parasitic Brain Abscess
Various protozoa and heliminths have been reported to produce brain abscess, including Trypanosomacruzi,
Entamoebahistolyitica, Schistosoma spp, and Paragonimus spp., Neurocysticcercosis , caused by the larval form of
Taneiasolium , is a major cause of brain lesions in the developing world [28, 29].
PATHOGENESIS
Microorganisms can reach the brain by several different mechanisms [3]. The most common pathogenic
mechanism of brain abscess formation spread from a contiguous focus of infection, most often in the middle ear, mastoid
cells, or paranasal sinuses. Brain abscess occurring secondary to otitis media is usually localized to temporal lobe or
cerebellum; in one review of 41 cases of brain abscess from anoctogenic source, 54% were in temporal lobe, 44% were in cerebellum, and 2% were in both location [15]. If antimicrobial therapy of otitis media is neglected, however there is an increased risk of intracranial complications [15]. Paranasal sinusitis continues to be an important condition predisposing to brain abscess. The frontal lobe is predominant abscess site, although when brain abscess complicates sphenoid sinusitis, the temporal lobe or sellaturcica is usually involved. Dental infections are a less common cause of brain abscess; infections of molar teeth seem most often to be the inciting factor. The frontal lobe is the usual site of the abscess after dental infection, but temporal lobe extension has also been reported [30].
Other mechanism of brain abscess formation is hematogenous dissemination from distant focus of infection.
These abscesses are usually multiple and multilocated, and they have a higher mortality rate than abscesses that arise
secondary to contiguous foci of infection [3]. The most common source of initial infection in adults are chronic lung
pyogenic lung disease, especially lung abscess, bronchiectasis. Empyema, and cystic fibrosis. Brain abscess may also occur hematogenously from wound skin infections, osteomyelitis, pelvic infection, choleocystitis, and other intra –abdominal infections. Another predisposing factor leading to hematogenous acquired brain abscess is cyanotic congenital heart disease, which account for about 5% to 15% of all brain abscess cases, with higher percentage in some pediatric
series [30].
Trauma is a pathogenic mechanismin the development of brain abscess. Brain abscess occurs secondary to an
open cranial fracture with dural breach, or as a result of neurosurgery or a foreign body injury [31]. The incidence of brain abscess formation after head trauma ranges from 3% to 17% in military populations, where it is secondary to retained bone fragments or contamination of initially “sterile” missile sites with bacteria from skin, clothes, and the environments [32].
In a study of 160 war missile penetrating craniocereberal injuries in Croatia in which 21 skull base injuries were treated
surgically. Three cases of brain abscess were seen for which repeat surgery was required [33]. Traumatic predisposing
conditions to brain abscess in the civilian population (incidence of 2.5% to10.9% after trauma) include depressed skull
fracture, dog bites, rooster pecking, tongue piercing, and, especially in children lawn darting and pencil tips [34].
CLINICAL PRESENTATION
A common misconception among physicians concerns the frequency with which fever is found during the initial
clinical presentation of brain abscess. In some cases fever occurs in