Focal neurologic findings and a positive CT or MRI. Blood cultures may be positive depending on the etiology, but best to get pus straight from the abscess. It is one of the few infections I can't get IR to go after.
Brain abscess occur from
3) reactivation of existing pathogens (toxoplasmosis in AIDS).
If a patient has a bacterial abscess for no damn good reason, look for pulmonary arteriovenous malformations and Hereditary Hemorrhagic Telangiectasia (PubMed).
If there is a brain abscess due to oral flora, look for a pulmonary arterial-venous malformation; also in association with dental work and increased iron (PubMed).
- Penetrating trauma: gram negative rods OR S. aureus.
- HIV: toxoplasmosis; in HIV the differential diagnosis is between toxoplasmosis and CNS lymphoma. If toxoplasma seronegative and a single lesion, its lymphoma. If toxoplasma seropositive and multiple lesions, treat for toxoplasma. If seropositive and single lesion, treat for toxoplasma and see if they are clinically/radiographically better in 10 days. If not, biopsy. If seronegative and multiple lesions, biopsy. Also Nocardia and Mycobacterium, Listeria monocytogenes and Cryptococcus neoformans.
- Steroid patients: Nocardia, especially if a concomitant lung infection/abscess.
These are what you can grow; using 16S rDNA multiple sequencing, and don't you wish you could, markedly increases the number of bacteria found: Streptococcus intermedius, Streptococcus constellatus, Streptococcus pneumoniae, Streptococcus anginosus, Staphylococcus aureus, Gemella haemolysans, Gemella morbillorum, Escherichia coli, Acinetobacter calcoaceticus, Eikenella corrodens, Klebsiella oxytoca, Serratia marcescens, Aggregatibacter aphrophilus, Micromonas micros, Fusobacterium nucleatum, Porphyromonas endodontalis, Porphyromonas gingivalis, Prevotella oris, Prevotella intermedia, Bacteroides fragilis, Nocardia cyriacigeorgia, Nocardia species Mycoplasma hominis, Fusobacterium naviforme, Staphylococcus epidermidis Mycoplasma faucium, Campylobacter gracilis, Peptostreptococcus stomatis, Eubacterium brachy, Mogibacterium timidum, Prevotella tannerae, Prevotella baroniae, Prevotella species (EU663611), Neisseria species (EU663609), Capnocytophaga species (EU663610), Campylobacter rectus, Treponema maltophilum, Und bacterium 1 (EU663600), Und bacterium 2 (EU663601), Und bacterium 3 (EU663602), Und bacterium 4 (EU663603), Und bacterium 5 (EU663604), Und bacterium 6 (EU663605), Und bacterium 7 (EU663606), Und bacterium 8 (EU663607), Und bacterium 9 (EU66308), Und Eubacterium E1-K13, Und Eubacterium E1-K9, Und Eubacterium species, Bacteroidales genomosp. oral clone, Und Prevotella species, Prevotella species oral clone DO033. Whoa (PubMed)(PubMed).
Varies according to the above infection and risks. For most brain abscesses, give a third generation cephalosporin AND metronidazole +/- vancomycin (especially if penetrating trauma or endocarditis) pending debridement/drainage.
But do not let the sunset on a brain abscess; delay in drainage increases morbidity and mortality (PubMed).
Duration of therapy is until cure (a negative CT as a rule), often 4 to 6 weeks of iv therapy for bacterial. See specific organism for therapy.
With the exception of toxoplasmosis and HIV, empiric therapy without cultures is way way stupid.
A significant number of brain abscesses will have no risk factors, LP is a BAD idea.
Every couple years I see a patient who has a "brain tumor" who is put on steroids for edema and instead has a brain abscess. Infections do not do real well when treated with steroids alone. Just sayin'.
Relevant links to my Medscape blog
Last Update: 05/23/18.