History and exam

Key diagnostic factors

common

presence of risk factors

Sinusitis, otitis media, recent dental procedure or infection, recent neurosurgery, meningitis, congenital heart disease, endocarditis, diverticular disease, hereditary haemorrhage telangiectasia, arteriovenous malformation, diabetes mellitus, HIV or immunocompromise, intravenous drug abuse, granulomatous disease, haemodialysis, or premature birth are strong risk factors.

male sex

Men are at slightly greater risk than women for developing a brain abscess.[2]​

age <30 years

Prevalence is highest in adult men younger than 30 years, while paediatric disease occurs most frequently in children aged 4 to 7 years. Neonates comprise a third at-risk group. The age of the patient is important in determining the most likely source of, and the most common aetiological agents for, brain abscess.

In neonates, Proteus mirabilis and Citrobacter species are the most common isolates, while in children Streptococcus species in combination with cyanotic heart disease is most often responsible for brain abscess.

In adults, brain abscess is most often due to sinusitis or otitis, and is most often caused by Streptococcus species.

meningismus

Meningismus does not usually represent a symptom of brain abscess, and its absence does not exclude this diagnosis. Nonetheless, it is an important neurological sign, because it is highly suggestive of brain abscess when present in combination with ring-enhancing lesion(s) in the brain.

headache

Persistent headache, signs or symptoms of increased intracranial pressure, and almost any neurological deficit should prompt urgent neuro-imaging studies.

cranial nerve palsy

Third or sixth cranial nerve palsies, anisocoria, and papilloedema should all prompt immediate imaging when encountered in an obtunded patient suspected of having brain abscess.

positive Kernig or Brudzinski sign

The test for Kernig sign is done with the patient lying supine, the thigh flexed at a right angle to the trunk, and the leg at the knee joint completely extended. If the leg cannot be completely extended due to pain, the examination is considered positive. With a positive Brudzinski sign, passive flexion of the leg on 1 side causes a similar movement in the opposite leg.

fever

Fever is a relatively common finding, but its absence does not exclude the diagnosis of brain abscess.

increased head circumference (infants)

Important in the examination of infants with suspected brain abscess.

bulging fontanelles (infants)

Important in the examination of infants with suspected brain abscess.

Other diagnostic factors

common

neurological deficit

May include motor or sensory findings. Although neurological deficit is very common in patients with brain abscess, it is neither particularly sensitive nor a specific finding. It is an important finding in that it is a clear indication for neuro-imaging, which is often the critical test for diagnosing brain abscess.

uncommon

papilloedema

Sign of increased intracranial pressure. Patients exhibiting this sign should be treated with particular caution. As with other neurological signs, papilloedema is neither sensitive nor specific for brain abscess.

Risk factors

strong

sinusitis

Most significant predisposing factor for adult brain abscess. May spread intracranially and manifest as uncomplicated meningitis, or subdural or epidural empyema.[7][8]

It should be determined whether or not the patient was treated with antibiotics. However, antibiotic treatment does not exclude the possibility of brain abscess.

otitis media

Infection by direct extension or thrombophlebitis of temporal emissary veins. Most often results in lesions in the cerebellum or temporal lobe, with Streptococcus species encountered most frequently.[9][10]

It should be determined whether or not the patient was treated with antibiotics. However, antibiotic treatment does not exclude the possibility of brain abscess.

dental procedure/infection

Dental infection or recent dental procedures are periodically described as causing brain abscess, but are infrequent relative to the frequency of these procedures and infections.[11][12][13] Spread may either be by direct extension or by haematogenous routes.

meningitis

In neonates and infants, meningitis caused by Proteus mirabilis, Escherichia coli, and Citrobacter species may become a source of brain abscesses. These are the most common isolates from brain abscesses in neonates.

recent head and neck surgery or neurosurgery

Abscess is a known complication of neurosurgical procedures and head and neck surgery.[2][14]​ Brain abscess after craniotomy should be an infrequent complication, with a higher risk for patients treated with prolonged corticosteroids.[15][16]​​ Halo placement, which involves percutaneous insertion of pins into the calvarium, can also be complicated by abscess formation.[17][18]

In this group of patients, a history of wound breakdown or drainage from the incision is highly suggestive for brain abscess. Streptococcus intermedius has emerged as a common aetiological agent in patients who have had recent head and neck surgery.

congenital heart disease

Congenital heart disease with the presence of right-to-left shunting is a major risk factor for the development of cerebral abscess in children.[7][19][20] Streptococcal, staphylococcal, and Haemophilus infections are most common in this group.

endocarditis

Endocarditis can lead to numerous neurological sequelae including brain abscess.[21][22] Most of these patients have left-sided valvular involvement.

hereditary haemorrhagic telangiectasia or arteriovenous malformation

Hereditary haemorrhagic telangiectasia is characterised by mucocutaneous telangiectasias. Brain abscess may be the initial presentation, with risk of brain abscess increased as much as 1000-fold.[24][25]Streptococcus species are the most common causative organisms.[26] Pulmonary arteriovenous malformation results in a right-to-left shunt, which predisposes to brain abscess.[26]

diabetes mellitus

A risk factor for the development of abscess, but may not be a risk factor for post-surgical abscess formation.[16]Nocardia, which is generally an opportunistic organism, has been reported in an otherwise healthy diabetic patient with brain abscess.[27]

HIV or immunocompromise

Meningitis, encephalitis, and brain abscess are frequent opportunistic infections in patients with HIV. HIV infection is an important subgroup with a distinct set of aetiological agents. Toxoplasma, fungal, and tuberculous abscess must be considered.[28] Primary and metastatic central nervous system neoplasms must be differentiated from brain abscess in HIV.

The proportion of abscesses due to immunocompromise has risen with increasing numbers of immunocompromised patients. In one cohort study conducted in Denmark, 40% of patients with brain abscess were immunocompromised.[29]​ Certain microbes such as Nocardia asteroides, as well as most fungal abscesses, are virtually always opportunistic infections.

intravenous drug use

Intravenous drug users are at an increased risk for developing brain abscess caused by skin flora (e.g., Staphylococcus species).

Also increases risk for HIV infection.

chronic granulomatous disease

Association with brain abscess has been reported. Aspergillus is frequently encountered in this setting.[30][31]

haemodialysis

Increased risk because of immunocompromise associated with renal failure, as well as repeated venipuncture.[32]

birth prematurity

In addition to both gram-negative and gram-positive bacteria, Aspergillus abscess is of particular concern.[33]

weak

diverticular disease

Cerebral abscess is a rare complication of diverticular disease.[23] Spread is haematogenous.

cystic fibrosis

There are several case reports of patients with cystic fibrosis and cerebral abscess.[34][35] These infections tend to be in patients with advanced disease and severe bronchiectasis.

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