Brain Abscess

VERSION: 1.1 CREATED: January 30, 2026 REVISED: January 30, 2026 STATUS: Approved

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DIAGNOSIS: Brain Abscess

ICD-10: G06.0 (Intracranial abscess), G06.2 (Extradural and subdural abscess, unspecified), B43.1 (Phaeomycotic brain abscess), A06.6 (Amebic brain abscess)

CPT CODES: 87040 (Blood cultures x2 (different sites)), 85025 (CBC with differential), 80053 (CMP (BMP + LFTs)), 86140 (CRP (C-reactive protein)), 85652 (ESR (erythrocyte sedimentation rate)), 84145 (Procalcitonin), 86900 (Type and screen), 83605 (Lactate), 87389 (HIV 1/2 antigen/antibody), 86777 (Toxoplasma IgG antibody (serum)), 87305 (Serum galactomannan), 87449 (Beta-D-glucan (serum)), 83930 (Serum osmolality), 87116 (AFB smear and culture), 87102 (Fungal cultures), 87327 (Cryptococcal antigen (serum + CSF)), 70460 (CT head with contrast), 70553 (MRI brain with and without contrast), 70450 (CT head without contrast), 71046 (Chest X-ray), 74177 (CT chest/abdomen/pelvis), 70486 (CT sinuses), 70480 (CT temporal bones), 93306 (Echocardiogram (TTE)), 70496 (CT angiography head (CTA)), 95700 (Continuous EEG (cEEG)), 93000 (ECG (12-lead)), 78816 (PET-CT brain), 89051 (Cell count with differential (tubes 1 and 4)), 84157 (Protein), 82945 (Glucose with paired serum), 96374 (Ceftriaxone), 96365 (Vancomycin)

SYNONYMS: Brain abscess, cerebral abscess, intracranial abscess, intracerebral abscess, pyogenic brain abscess, brain infection, intracranial infection, cerebral suppuration, focal intracranial infection, ring-enhancing lesion

SCOPE: Diagnosis, antimicrobial treatment, surgical management, and follow-up of brain abscess in adults. Covers empiric antibiotic selection based on suspected source, indications for surgical drainage (stereotactic aspiration vs. craniotomy with excision), management of associated complications (seizures, elevated ICP, cerebral edema), prolonged IV antibiotic course monitoring, serial imaging for resolution, and source control. Includes special populations (immunocompromised: Toxoplasma, Nocardia, fungi). Excludes epidural abscess (separate template), subdural empyema, and pediatric brain abscess.

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PRIORITY KEY: STAT = Immediate | URGENT = Within hours | ROUTINE = Standard | EXT = Extended/atypical cases | - = Not applicable to this setting

═══════════════════════════════════════════════════════════════ SECTION A: ACTION ITEMS ═══════════════════════════════════════════════════════════════

1. LABORATORY WORKUP

1A. Essential/Core Labs

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
Blood cultures x2 (different sites) (CPT 87040)	STAT	STAT	-	STAT	Draw BEFORE antibiotics; positive in 25-50% of brain abscess cases; identifies organism for targeted therapy; higher yield if hematogenous source	Organism identification and sensitivities; Streptococci most common overall
CBC with differential (CPT 85025)	STAT	STAT	ROUTINE	STAT	Leukocytosis present in only 40-60%; left shift; baseline for monitoring antibiotic toxicity; thrombocytopenia may indicate DIC	WBC elevated in 40-60%; normal WBC does NOT exclude brain abscess; neutrophilia
CMP (BMP + LFTs) (CPT 80053)	STAT	STAT	ROUTINE	STAT	Renal function for antibiotic dosing (metronidazole, vancomycin); electrolytes; hepatic function for metronidazole clearance; glucose (diabetes risk factor)	Normal; monitor renal and hepatic function during prolonged antibiotic course
CRP (C-reactive protein) (CPT 86140)	STAT	STAT	ROUTINE	STAT	Elevated in >80% of brain abscess; useful for monitoring treatment response; correlates with abscess activity	Elevated; declining trend indicates treatment response
ESR (erythrocyte sedimentation rate) (CPT 85652)	STAT	STAT	ROUTINE	STAT	Elevated in 60-80% of brain abscess; less responsive to acute changes than CRP; useful for longitudinal monitoring	Elevated (typically 40-80 mm/hr); declining trend with successful treatment
Procalcitonin (CPT 84145)	STAT	STAT	-	STAT	Helps distinguish bacterial from non-infectious etiology; may be normal in well-encapsulated abscess without systemic infection	Variable; elevated if systemic sepsis present; may be normal with contained abscess
PT/INR, aPTT (CPT 85610+85730)	STAT	STAT	-	STAT	Coagulopathy assessment before surgical intervention; DIC screening; baseline before anticoagulation decisions	Normal; correct if abnormal before surgery
Blood glucose / HbA1c (CPT 82947+83036)	STAT	STAT	ROUTINE	STAT	Diabetes is risk factor for brain abscess; uncontrolled glucose impairs immune response and wound healing	HbA1c <6.5% (normal); glucose <180 mg/dL target
Type and screen (CPT 86900)	STAT	STAT	-	STAT	Surgical candidacy; blood product availability for craniotomy or stereotactic aspiration	On file
Lactate (CPT 83605)	STAT	STAT	-	STAT	Sepsis assessment in patients with systemic toxicity	<2 mmol/L; elevated suggests sepsis requiring aggressive resuscitation

1B. Extended Workup (Second-line)

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
HIV 1/2 antigen/antibody (CPT 87389)	-	ROUTINE	ROUTINE	ROUTINE	Immunocompromise expands differential (Toxoplasma, Nocardia, fungi); affects empiric coverage and prognosis	Negative; if positive: CD4 count, viral load; consider opportunistic organisms
CD4 count (if HIV positive)	-	ROUTINE	ROUTINE	-	CD4 <200: Toxoplasma, Nocardia, Aspergillus, Mucor, Cryptococcus; affects empiric coverage	>200 cells/mm3; if <200: broaden empiric coverage
Toxoplasma IgG antibody (serum) (CPT 86777)	-	ROUTINE	ROUTINE	ROUTINE	If HIV/immunocompromised with ring-enhancing lesion; IgG positive in >95% of toxoplasma brain abscess	Negative in immunocompetent; positive IgG + HIV + ring-enhancing lesions = empiric treatment for Toxoplasma
Hepatitis B/C serologies	-	ROUTINE	ROUTINE	-	IVDU population (risk factor); affects long-term antibiotic selection; hepatotoxicity monitoring	Negative; if positive: affects drug selection
Serum galactomannan (CPT 87305)	-	ROUTINE	-	ROUTINE	Aspergillus in immunocompromised (transplant, neutropenia, chronic steroid use); supports fungal abscess diagnosis	Negative (<0.5 index); positive suggests invasive aspergillosis
Beta-D-glucan (serum) (CPT 87449)	-	ROUTINE	-	ROUTINE	Broad fungal screening in immunocompromised patients; positive in Aspergillus, Candida, Pneumocystis	Negative (<60 pg/mL); elevated suggests invasive fungal infection
Nocardia culture (modified acid-fast stain)	-	ROUTINE	-	ROUTINE	Immunocompromised; chronic steroid use; transplant; may require prolonged culture (2-3 weeks)	Negative; positive: branching gram-positive filamentous rods
Immunoglobulin levels (IgG, IgA, IgM)	-	ROUTINE	ROUTINE	-	Hypogammaglobulinemia predisposes to recurrent infections; consider if recurrent or atypical abscess	Normal range
Complement levels (CH50, C3, C4)	-	ROUTINE	ROUTINE	-	Complement deficiency predisposes to infections; consider if recurrent or unusual organisms	Normal
Serum osmolality (CPT 83930)	URGENT	ROUTINE	-	URGENT	SIADH assessment (common complication with intracranial pathology)	280-295 mOsm/kg

1C. Rare/Specialized (Refractory or Atypical)

Test	ED	HOSP	OPD	ICU	Rationale	Target Finding
Abscess aspirate culture (aerobic + anaerobic + fungal + AFB)	-	STAT	-	STAT	Gold standard for organism identification; sensitivity 70-90% from surgical specimens; send for Gram stain, aerobic, anaerobic, fungal, and mycobacterial culture	Organism identification; polymicrobial in 20-30%; anaerobes in 30-40%
16S rRNA PCR (on abscess tissue)	-	EXT	-	EXT	Culture-negative abscess; prior antibiotic exposure; fastidious or slow-growing organisms	Identifies organism even when cultures negative due to prior antibiotics
Metagenomic next-generation sequencing (mNGS) of abscess fluid	-	EXT	-	EXT	Culture-negative abscess; atypical organisms; prior prolonged antibiotic therapy	Comprehensive pathogen detection
Histopathology (abscess wall)	-	ROUTINE	-	-	Distinguish abscess from necrotic tumor (GBM, metastasis); granulomatous inflammation (TB, fungal); demyelination (tumefactive MS)	Purulent material, neutrophilic infiltrate, necrosis with surrounding gliosis; no malignant cells
AFB smear and culture (CPT 87116)	-	EXT	EXT	-	Tuberculoma in endemic areas; immunocompromised; granulomatous abscess; chronic presentation	Negative; positive: TB requires different treatment (anti-TB regimen 9-12 months)
Fungal cultures (CPT 87102)	-	EXT	EXT	-	Immunocompromised; transplant; endemic fungi (Coccidioides, Histoplasma, Blastomyces); Aspergillus, Mucor	Negative; positive: prolonged antifungal therapy (6-12+ months)
QuantiFERON-TB Gold	-	ROUTINE	ROUTINE	-	TB abscess (tuberculoma) in high-risk patients; endemic areas; immunocompromised	Negative
Actinomyces culture	-	EXT	EXT	-	Dental source; cervicofacial disease; sulfur granules on histology; requires prolonged anaerobic culture (14 days)	Negative; positive: prolonged penicillin/amoxicillin therapy (6-12 months)
Cryptococcal antigen (serum + CSF) (CPT 87327)	-	ROUTINE	-	ROUTINE	HIV/immunocompromised; cryptococcoma (solid form of cryptococcal infection)	Negative

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2. DIAGNOSTIC IMAGING & STUDIES

2A. Essential/First-line

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
CT head with contrast (CPT 70460)	STAT	STAT	-	STAT	Immediate. First-line in ED for any patient presenting with headache + fever + focal deficits	Ring-enhancing lesion with central hypodensity (necrosis) and surrounding vasogenic edema; thin smooth enhancing wall; may show mass effect, midline shift, hydrocephalus	Contrast allergy (pre-medicate or use MRI); renal impairment (hydrate)
MRI brain with and without contrast (CPT 70553)	STAT	STAT	ROUTINE	STAT	Within 24h if CT suspicious; STAT if available. Gold standard imaging for brain abscess	DWI restriction (bright on DWI, dark on ADC) = abscess (distinguishes from necrotic tumor); ring enhancement; T2/FLAIR hyperintensity of surrounding edema; thin smooth wall; multiloculated collections	Pacemaker, metallic implants; claustrophobia (sedate)
CT head without contrast (CPT 70450)	STAT	STAT	-	STAT	Immediate if concern for herniation before contrast; follow-up imaging to assess mass effect	Mass effect, midline shift, hydrocephalus, hemorrhage	Pregnancy (relative)
Chest X-ray (CPT 71046)	URGENT	ROUTINE	ROUTINE	URGENT	Within first hours	Lung abscess, pneumonia (hematogenous source); AVM (hereditary hemorrhagic telangiectasia); endocarditis-related septic emboli	None significant

2B. Extended

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
MR spectroscopy (MRS)	-	ROUTINE	ROUTINE	-	When diagnosis uncertain (abscess vs. tumor)	Amino acid peaks (valine, leucine, isoleucine), succinate, acetate, lactate = abscess; choline elevation = tumor; helps differentiate when DWI equivocal	Same as MRI
CT chest/abdomen/pelvis (CPT 74177)	-	ROUTINE	ROUTINE	-	Source identification; within 48-72h	Lung abscess, pulmonary AVM, endocarditis, abdominal abscess, dental pathology source	Contrast allergy; renal impairment
Dental panoramic radiograph (Panorex)	-	ROUTINE	ROUTINE	-	Source identification; odontogenic source is common (25-30% of brain abscesses)	Dental abscess, apical pathology, periodontal disease	None significant
CT sinuses (CPT 70486)	-	ROUTINE	ROUTINE	-	If sinogenic source suspected (frontal lobe abscess)	Sinusitis; Pott puffy tumor; mucocele; osteomyelitis of frontal bone	Contrast allergy
CT temporal bones (CPT 70480)	-	ROUTINE	ROUTINE	-	If otogenic source suspected (temporal lobe or cerebellar abscess)	Mastoiditis, cholesteatoma, middle ear disease, tegmen defect	None significant
Echocardiogram (TTE) (CPT 93306)	-	ROUTINE	ROUTINE	ROUTINE	Source identification; endocarditis screen; especially with S. aureus or multiple abscesses	Vegetations, patent foramen ovale (paradoxical embolism), septal defects	None significant
TEE (transesophageal echo)	-	URGENT	-	URGENT	If TTE non-diagnostic and high clinical suspicion for endocarditis or intracardiac shunt	Vegetations, PFO, ASD; TEE sensitivity 90-95% vs. TTE 65%	Esophageal pathology
CT angiography head (CTA) (CPT 70496)	-	ROUTINE	-	ROUTINE	If mycotic aneurysm suspected (endocarditis-related); vascular malformation	Mycotic aneurysm; AVM	Contrast allergy; renal impairment
Continuous EEG (cEEG) (CPT 95700)	-	URGENT	-	STAT	If altered mental status persists or unexplained neurological decline; seizure detection	Seizure activity, non-convulsive status epilepticus	None significant
ECG (12-lead) (CPT 93000)	URGENT	ROUTINE	-	URGENT	Baseline; endocarditis screen; QTc for medication interactions	Normal; arrhythmia; conduction abnormality	None

2C. Rare/Specialized

Study	ED	HOSP	OPD	ICU	Timing	Target Finding	Contraindications
CT-guided stereotactic biopsy/aspiration	-	URGENT	-	-	Diagnostic and therapeutic; within 24-48h for accessible lesions	Purulent material; organism identification on culture; decompression of abscess	Coagulopathy (correct first); inaccessible location
PET-CT brain (CPT 78816)	-	-	EXT	-	If abscess vs. high-grade tumor remains unclear after MRI with DWI and MRS	Abscess: peripheral FDG uptake (ring pattern); tumor: diffuse uptake	Pregnancy; uncontrolled diabetes
Bubble echocardiogram	-	ROUTINE	ROUTINE	-	If multiple abscesses with no clear source; evaluate for right-to-left cardiac shunt (PFO)	Positive bubble study = right-to-left shunt (paradoxical embolism from venous to arterial)	None significant
Pulmonary angiography / CT chest with contrast	-	ROUTINE	ROUTINE	-	If pulmonary AVM suspected (hereditary hemorrhagic telangiectasia); multiple brain abscesses	Pulmonary AVM (bypasses pulmonary capillary filter)	Contrast allergy
ICP monitoring (EVD)	-	-	-	URGENT	If clinical signs of elevated ICP; declining GCS despite medical management	ICP <22 mmHg; CPP >60	Coagulopathy (correct first)

LUMBAR PUNCTURE

Indication: Generally CONTRAINDICATED in brain abscess due to risk of herniation. LP should NOT be performed if brain abscess is suspected or confirmed.

When LP may be considered: Only if meningitis is a concurrent concern AND imaging shows no significant mass effect, midline shift, or posterior fossa lesion. Even then, proceed with extreme caution.

Volume Required: 10-15 mL if performed

Study	ED	HOSP	OPD	Rationale	Target Finding
Opening pressure	URGENT	ROUTINE	-	Elevated ICP assessment (expected elevated with mass lesion)	Elevated (often >200 mm H2O); markedly elevated is common
Cell count with differential (tubes 1 and 4) (CPT 89051)	URGENT	ROUTINE	-	Mixed pleocytosis; may be normal if abscess well-encapsulated and not ruptured into ventricles	Variable: WBC 10-500 with mixed neutrophils and lymphocytes; may be normal
Protein (CPT 84157)	URGENT	ROUTINE	-	Typically mildly to moderately elevated	Elevated (50-200 mg/dL)
Glucose with paired serum (CPT 82945)	URGENT	ROUTINE	-	Usually normal unless abscess has ruptured into ventricle (ventriculitis)	Normal or mildly low; markedly low suggests ventriculitis or concurrent meningitis
Gram stain and bacterial culture (CPT 87205+87070)	URGENT	ROUTINE	-	Low yield in brain abscess (positive in <25%); may be positive if ventriculitis	Usually negative; positive with intraventricular rupture
Fungal culture (CPT 87102)	-	ROUTINE	-	If immunocompromised or fungal abscess suspected	Negative
AFB smear and culture (CPT 87116)	-	ROUTINE	-	If tuberculoma suspected	Negative

Special Handling: CSF culture has very low diagnostic yield in brain abscess. Surgical aspiration of the abscess itself is the gold standard for organism identification.

Contraindications: Brain abscess with mass effect (HIGH RISK of herniation); posterior fossa abscess; midline shift; obstructive hydrocephalus. LP is relatively contraindicated in most cases of confirmed brain abscess.

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3. TREATMENT

CRITICAL: TREATMENT APPROACH

Brain abscess requires a dual approach: prolonged antimicrobial therapy AND surgical intervention in most cases. Antibiotics alone may suffice for small (<2.5 cm), deep-seated lesions or early cerebritis stage.

Sequence: 1. Blood cultures (before antibiotics if obtainable without delay) 2. Empiric IV antibiotics STAT 3. CT/MRI to confirm diagnosis 4. Neurosurgery consultation for aspiration/excision 5. Targeted antibiotics based on culture results 6. 6-8 weeks total IV antibiotic course 7. Serial imaging to confirm resolution

3A. Acute/Emergent

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Ceftriaxone (CPT 96374)	IV	Empiric broad-spectrum coverage for Streptococci, gram-negatives, H. influenzae; penetrates blood-brain barrier well	2 g :: IV :: q12h :: 2 g IV q12h; duration 6-8 weeks total IV therapy; adjust based on culture results	Cephalosporin anaphylaxis (use meropenem as alternative); biliary sludge with prolonged use	CBC weekly; LFTs biweekly; renal function weekly; biliary symptoms	STAT	STAT	-	STAT
Metronidazole (CPT 96374)	IV	Empiric anaerobic coverage (Bacteroides, Fusobacterium, Prevotella); excellent CNS penetration; essential for abscess from dental, sinus, or otogenic source	500 mg :: IV :: q8h :: 500 mg IV q8h; then transition to 500 mg PO q8h when clinically stable; duration 6-8 weeks total; excellent oral bioavailability allows early PO switch	Disulfiram-like reaction with alcohol; first-trimester pregnancy; severe hepatic impairment	Peripheral neuropathy with prolonged use (>4 weeks: reassess); LFTs; metallic taste; seizure threshold	STAT	STAT	-	STAT
Vancomycin (CPT 96365)	IV	ADD if: post-surgical/post-traumatic abscess, MRSA risk, penetrating trauma, or unknown source; covers MRSA and penicillin-resistant Streptococci	15-20 mg/kg :: IV :: q8-12h :: 15-20 mg/kg IV q8-12h; target trough 15-20 ug/mL or AUC/MIC 400-600; loading dose 25-30 mg/kg for severe cases	Renal impairment (dose adjust); red man syndrome (infuse over >=1h)	Trough levels before 4th dose then q48-72h; renal function daily initially then twice weekly; ototoxicity	STAT	STAT	-	STAT
Dexamethasone (CPT 96374)	IV	Significant mass effect, cerebral edema, impending herniation, or declining neurologic status; NOT routine for all brain abscesses; may reduce antibiotic penetration	10 mg :: IV :: q6h :: 10 mg IV q6h (0.15 mg/kg q6h) for 48-72h then rapid taper over 5-7 days; use ONLY for significant edema/mass effect; taper as soon as clinically feasible	Active untreated infection (relative; benefit of edema reduction may outweigh risk); may impair abscess encapsulation	Glucose q6h; GI prophylaxis; blood pressure; taper schedule; do NOT use prolonged course	STAT	STAT	-	STAT
Levetiracetam (seizure prophylaxis) (CPT 96374)	IV	Seizure prophylaxis in brain abscess (seizure incidence 25-50%); recommended for all supratentorial abscesses, especially frontal and temporal locations	1000 mg :: IV :: BID :: 1000 mg IV load; then 500-1000 mg IV/PO BID; titrate to 1500 mg BID if needed; max 3000 mg/day; continue for at least 3-6 months after resolution	Severe renal impairment (dose adjust CrCl <30)	Renal function; behavioral/mood changes; CBC	STAT	STAT	ROUTINE	STAT
Mannitol 20%	IV	Elevated ICP management; acute cerebral herniation; bridge to surgical decompression	1 g/kg :: IV :: bolus then 0.25-0.5 g/kg q4-6h :: 1-1.5 g/kg IV bolus over 20 min; then 0.25-0.5 g/kg q4-6h PRN for ICP >22; hold if serum osm >320	Anuria; severe dehydration; active intracranial bleeding	Serum osmolality (<320 mOsm/kg); osmolar gap; renal function; serum Na; I/O	STAT	-	-	STAT
Hypertonic saline 23.4%	IV	Acute herniation syndrome; more sustained ICP reduction than mannitol	30 mL :: IV :: once over 10-20 min :: 30 mL via central line over 10-20 min; target Na 145-155 mEq/L; may repeat PRN	No central access (peripheral administration causes tissue necrosis)	Serum Na q4-6h; osmolality; central line access confirmed	STAT	-	-	STAT
IV normal saline	IV	Maintenance fluids; avoid hypotonic solutions which worsen cerebral edema	0.9% NaCl :: IV :: continuous at 75-125 mL/h :: Isotonic fluids only; avoid D5W and half-normal saline; maintain euvolemia	Volume overload; CHF	I/O; electrolytes daily; serum Na	STAT	STAT	-	STAT

3B. Symptomatic Treatments

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Lorazepam (seizure rescue)	IV	Active seizure; breakthrough seizure on prophylaxis	4 mg :: IV :: push PRN seizure :: 0.1 mg/kg IV (max 4 mg) over 2 min; may repeat x1 in 5 min; max 8 mg total	Respiratory depression; severe hypotension	Respiratory rate; SpO2; blood pressure; airway equipment at bedside	STAT	STAT	-	STAT
Acetaminophen	PO/IV	Fever management; headache; temperature goal <38C to reduce cerebral metabolic demand	1000 mg :: PO :: q6h PRN :: 650-1000 mg PO/IV q6h; max 4 g/day; IV route if unable to take PO	Severe hepatic disease; metronidazole concurrent use (monitor LFTs closely)	Temperature; LFTs (especially with concurrent metronidazole)	STAT	STAT	ROUTINE	STAT
Ondansetron	IV	Nausea and vomiting (common with elevated ICP and metronidazole use)	4 mg :: IV :: q6h PRN :: 4 mg IV/PO q6h PRN nausea; max 16 mg/day	QT prolongation; severe hepatic impairment (max 8 mg/day)	QTc if risk factors; hepatic function	STAT	ROUTINE	-	STAT
Pantoprazole	IV	GI prophylaxis with steroids and critical illness; stress ulcer prevention	40 mg :: IV :: daily :: 40 mg IV/PO daily; discontinue when steroids stopped and no longer in ICU	Long-term use risks (C. diff, hypomagnesemia); only while on steroids or in ICU	GI symptoms; consider discontinuation when steroids stopped	-	ROUTINE	-	ROUTINE
Enoxaparin	SC	DVT prophylaxis; prolonged immobilization and hospitalization are significant VTE risk factors	40 mg :: SC :: daily :: 40 mg SC daily; start 24-48h post-surgery if no active bleeding; hold if upcoming surgery	Active intracranial bleeding; recent craniotomy (<24h); coagulopathy; platelets <50K	Platelets q3 days (HIT monitoring); coagulation panel; clinical DVT signs	-	ROUTINE	-	ROUTINE
Pneumatic compression devices	Mechanical	DVT prophylaxis; apply on admission; use in conjunction with pharmacologic prophylaxis when safe	Bilateral :: Mechanical :: continuous :: Bilateral sequential compression devices; apply on admission; use from admission through ambulation	Acute DVT in lower extremity; severe peripheral vascular disease	Skin integrity; proper fit; compliance	STAT	STAT	-	STAT
Fosphenytoin (seizure rescue second-line)	IV	Refractory seizure not responding to levetiracetam; status epilepticus protocol	20 mg PE/kg :: IV :: load then 100 mg PE q8h :: Fosphenytoin 20 mg PE/kg IV at 150 mg PE/min; maintenance 100 mg PE q8h; target free phenytoin level 1-2 ug/mL (total 10-20 ug/mL)	Bradycardia; second/third-degree heart block; hypotension	Continuous telemetry during load; free phenytoin level; LFTs; CBC	STAT	STAT	-	STAT

3C. Second-line/Refractory — Targeted Therapy by Source and Organism

Treatment	Route	Indication	Dosing	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Penicillin G	IV	Targeted therapy for penicillin-sensitive Streptococci (most common brain abscess isolate); adjust based on culture sensitivities	4 million units :: IV :: q4h :: 4 million units IV q4h (24 million units/day); duration 6-8 weeks total; excellent CNS penetration	Penicillin anaphylaxis; use ceftriaxone or meropenem alternative	Renal function; CBC; rash; interstitial nephritis with prolonged use	-	STAT	-	STAT
Meropenem	IV	Broad-spectrum alternative if cephalosporin allergy; ESBL gram-negative organisms; polymicrobial abscess; Nocardia (some species)	2 g :: IV :: q8h :: 2 g IV q8h (meningitic dosing for CNS penetration); duration 6-8 weeks	Carbapenem allergy; lowers seizure threshold (less than imipenem)	Renal function; CBC; seizure monitoring; LFTs	-	STAT	-	STAT
TMP-SMX (Trimethoprim-Sulfamethoxazole)	IV/PO	Nocardia brain abscess (first-line); Toxoplasma alternative; Stenotrophomonas	5 mg/kg TMP :: IV :: q6-8h :: 5 mg/kg IV q6-8h based on TMP component; transition to PO when stable; Nocardia: treat 6-12 months total	Sulfa allergy; G6PD deficiency; severe renal impairment; megaloblastic anemia from folate deficiency	Renal function; CBC weekly (cytopenias); potassium (hyperkalemia); LFTs; rash (Stevens-Johnson risk)	-	STAT	ROUTINE	STAT
Pyrimethamine	PO	Toxoplasma brain abscess (first-line); HIV/AIDS with CD4 <100 and ring-enhancing lesions; MUST co-administer with sulfadiazine and leucovorin	200 mg :: PO :: load x1 then 50-75 mg daily :: Pyrimethamine 200 mg PO load x1, then 50-75 mg PO daily; treat 6 weeks minimum then maintenance; always co-administer with sulfadiazine and leucovorin	Bone marrow suppression; megaloblastic anemia; must give leucovorin concurrently	CBC twice weekly x 2 weeks then weekly; LFTs; renal function; leucovorin compliance essential	-	STAT	ROUTINE	STAT
Sulfadiazine	PO	Toxoplasma brain abscess (first-line); used in combination with pyrimethamine and leucovorin	1-1.5 g :: PO :: q6h :: 1-1.5 g PO q6h; treat 6 weeks minimum then maintenance; maintain adequate hydration to prevent crystalluria	Sulfa allergy (use clindamycin as alternative); severe renal impairment; crystalluria risk	Renal function; urinalysis for crystalluria; hydration status; CBC; rash (Stevens-Johnson risk)	-	STAT	ROUTINE	STAT
Leucovorin (folinic acid)	PO	Prevent pyrimethamine-induced bone marrow suppression; MUST co-administer with pyrimethamine	10-25 mg :: PO :: daily :: 10-25 mg PO daily; continue throughout pyrimethamine therapy and 1 week after discontinuation	None significant	CBC; signs of myelosuppression	-	ROUTINE	ROUTINE	ROUTINE
Voriconazole	IV/PO	Aspergillus brain abscess (first-line); other mold infections in immunocompromised	6 mg/kg :: IV :: q12h x2 load then 4 mg/kg q12h :: 6 mg/kg IV q12h x 2 loading doses, then 4 mg/kg IV q12h; transition to 200-300 mg PO BID when stable; duration 6-12 months minimum	Hepatic impairment; concurrent strong CYP3A4 inducers (rifampin, carbamazepine); QT prolongation; visual disturbances; IV form contraindicated if CrCl <50 (cyclodextrin accumulation)	Voriconazole trough levels (target 2-5 ug/mL); LFTs weekly initially then biweekly; visual changes; QTc; drug interactions (CYP2C19 polymorphisms)	-	STAT	ROUTINE	STAT
Amphotericin B (liposomal)	IV	Mucormycosis brain abscess; severe/refractory fungal abscess; amphotericin-sensitive fungi when azoles inadequate	5 mg/kg :: IV :: daily :: 5 mg/kg IV daily; infuse over 2h; duration based on clinical response (typically 4-6 weeks IV then transition to oral azole); pre-medicate with acetaminophen and diphenhydramine	Renal impairment (liposomal less nephrotoxic than conventional); infusion reactions	Renal function daily; electrolytes daily (K, Mg -- wasting common); CBC; infusion reactions; pre-medicate	-	STAT	-	STAT
Linezolid	IV/PO	MRSA brain abscess alternative to vancomycin; excellent CNS penetration; useful when vancomycin levels difficult to maintain	600 mg :: IV :: q12h :: 600 mg IV/PO q12h; 100% oral bioavailability; duration limited to 4 weeks ideally due to toxicity (use vancomycin for remainder)	Concurrent MAOIs; serotonergic agents; thrombocytopenia; duration >4 weeks increases toxicity risk	CBC weekly (thrombocytopenia, anemia); peripheral neuropathy; lactic acidosis; optic neuritis (rare but serious with prolonged use >28 days); serotonin syndrome risk	-	STAT	ROUTINE	STAT
Fluconazole	IV/PO	Candida brain abscess (uncommon); Cryptococcus consolidation therapy after amphotericin induction	800 mg :: IV :: daily :: 800 mg IV/PO daily x 2 weeks induction (with amphotericin for Crypto), then 400 mg PO daily consolidation x 8 weeks; maintenance 200 mg PO daily for Crypto in HIV	Hepatic impairment; QT prolongation; concurrent terfenadine/cisapride	LFTs biweekly; QTc; drug interactions (CYP2C9/3A4 inhibitor)	-	STAT	ROUTINE	STAT

3D. Surgical Management (Disease-Modifying)

Treatment	Route	Indication	Dosing	Pre-Treatment Requirements	Contraindications	Monitoring	ED	HOSP	OPD	ICU
Stereotactic aspiration (CT or MRI-guided)	Surgical	Brain abscess >2.5 cm; deep-seated abscess not amenable to open excision; diagnostic aspiration for culture; therapeutic decompression	N/A :: Surgical :: once :: Single aspiration; may be repeated if re-accumulation occurs; performed under stereotactic guidance	CT/MRI navigation imaging; coagulation panel (INR <1.5, platelets >100K); type and screen; neurosurgery consultation; anesthesia clearance	Coagulopathy (correct first); inaccessible brainstem location (relative)	Post-procedure CT within 24h; neurologic exam q1h x 6h then q2h; wound site; new deficits; fever; signs of hemorrhage	-	STAT	-	STAT
Craniotomy with excision	Surgical	Multiloculated abscess; posterior fossa abscess causing hydrocephalus; fungal abscess (poor antibiotic penetration); traumatic abscess with foreign body; failed aspiration (re-accumulation); abscess wall thicker than 5 mm with mature capsule	N/A :: Surgical :: once :: Complete excision via craniotomy; definitive treatment with lower recurrence rate than aspiration	CT/MRI navigation; coagulation panel; type and crossmatch; neurosurgery and anesthesia; medical optimization	Multiple deep abscesses; eloquent cortex location (relative; stereotactic aspiration preferred); severe medical comorbidities precluding general anesthesia	Post-operative neurologic exam q1h x 12h then q2h; CT at 24h; wound care; drain output; ICP if EVD placed; seizure monitoring	-	STAT	-	STAT
External ventricular drain (EVD)	Surgical	Intraventricular rupture of abscess (ventriculitis); obstructive hydrocephalus from mass effect; ICP monitoring and CSF drainage	N/A :: Surgical :: once :: Continuous or intermittent CSF drainage; target ICP <22 mmHg; target CPP >60 mmHg	Coagulation panel; type and screen; neurosurgery; CT confirmation of hydrocephalus	Severe coagulopathy (correct first)	ICP continuous; CSF output hourly; CSF Gram stain and culture daily; EVD site care; neurologic exam q1h	-	-	-	STAT

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4. OTHER RECOMMENDATIONS

4A. Referrals & Consults

Recommendation	ED	HOSP	OPD	ICU
Neurosurgery consultation for all brain abscesses for surgical planning (aspiration vs. excision vs. medical management decision)	STAT	STAT	-	STAT
Infectious disease consultation for antimicrobial optimization, targeted therapy selection, and duration guidance	STAT	STAT	ROUTINE	STAT
Neurology consultation for seizure management, EEG interpretation, and antiepileptic drug optimization	URGENT	URGENT	ROUTINE	STAT
ENT/Otolaryngology consultation for source control if otogenic or sinogenic origin suspected (mastoiditis, cholesteatoma, sinusitis)	-	URGENT	ROUTINE	-
Dental/Oral surgery consultation for source control if odontogenic origin suspected (dental abscess, periodontal disease)	-	URGENT	ROUTINE	-
Cardiology consultation for echocardiography and endocarditis evaluation if hematogenous source or S. aureus bacteremia	-	ROUTINE	ROUTINE	ROUTINE
Pulmonology consultation if pulmonary AVM suspected (hereditary hemorrhagic telangiectasia) or concurrent lung abscess	-	ROUTINE	ROUTINE	-
Critical care/ICU team for hemodynamic instability, ICP management, respiratory failure, or post-operative monitoring	STAT	STAT	-	STAT
PICC line/vascular access team for long-term IV access (6-8 week antibiotic course requiring reliable central venous access)	-	ROUTINE	-	-
Outpatient parenteral antibiotic therapy (OPAT) service for discharge planning and home IV antibiotic administration	-	ROUTINE	ROUTINE	-
Physical therapy for early mobilization, deconditioning prevention, and focal deficit rehabilitation	-	ROUTINE	ROUTINE	-
Occupational therapy for ADL assessment and cognitive rehabilitation if frontal or parietal lobe involvement	-	ROUTINE	ROUTINE	-
Speech-language pathology for swallow evaluation and language assessment if temporal lobe or dominant hemisphere involvement	-	ROUTINE	ROUTINE	-
Social work for discharge planning, home IV antibiotic coordination, and community resources	-	ROUTINE	ROUTINE	-
Immunology referral for recurrent or atypical brain abscess to evaluate for immunodeficiency syndromes	-	ROUTINE	ROUTINE	-

4B. Patient Instructions

Recommendation	ED	HOSP	OPD	ICU
Return to ED immediately if worsening headache, new confusion, seizure, fever recurrence, new weakness, vision changes, or vomiting (may indicate abscess enlargement, re-accumulation, or ventriculitis)	STAT	STAT	ROUTINE	-
Complete the full 6-8 week IV antibiotic course without interruption (premature discontinuation risks relapse and treatment failure)	-	ROUTINE	ROUTINE	-
Report any signs of PICC line infection: redness, swelling, drainage at line site, or new fever during home IV therapy	-	ROUTINE	ROUTINE	-
Report numbness, tingling, or pain in hands/feet which may indicate metronidazole-induced peripheral neuropathy requiring medication change	-	ROUTINE	ROUTINE	-
Do NOT consume alcohol during and for 48 hours after metronidazole therapy due to severe disulfiram-like reaction (nausea, vomiting, flushing, tachycardia)	-	ROUTINE	ROUTINE	-
Follow-up MRI scans are essential to confirm abscess resolution (typically at 2, 4, and 8 weeks during treatment, then every 2-3 months until resolved)	-	ROUTINE	ROUTINE	-
Do NOT drive until cleared by neurology due to seizure risk (seizures occur in 25-50% of brain abscess; state laws typically require 3-12 months seizure-free)	-	ROUTINE	ROUTINE	-
Take antiepileptic medications as prescribed; do NOT stop abruptly (risk of breakthrough seizure)	-	ROUTINE	ROUTINE	-
Follow-up with neurosurgery in 2-4 weeks for post-operative evaluation and imaging review	-	ROUTINE	ROUTINE	-
Follow-up with infectious disease in 1-2 weeks after discharge for antibiotic response assessment and lab monitoring	-	ROUTINE	ROUTINE	-
Notify healthcare team immediately if PICC line becomes occluded, dislodged, or if unable to infuse medications (line malfunction delays critical antibiotic doses)	-	ROUTINE	ROUTINE	-
Keep a daily symptom diary including temperature, headache severity, and any new neurologic symptoms to share with medical team at follow-up visits	-	ROUTINE	ROUTINE	-

4C. Lifestyle & Prevention

Recommendation	ED	HOSP	OPD	ICU
Dental evaluation and treatment of all dental pathology to prevent odontogenic brain abscess recurrence (dental source accounts for 25-30% of cases)	-	ROUTINE	ROUTINE	-
Smoking cessation to reduce sinusitis and upper respiratory infection risk which predispose to CNS infection	-	ROUTINE	ROUTINE	-
Alcohol cessation during antibiotic therapy (metronidazole interaction) and to support immune function	-	ROUTINE	ROUTINE	-
IV drug use cessation counseling and harm reduction (IVDU is major risk factor for hematogenous brain abscess especially right-to-left shunt)	-	ROUTINE	ROUTINE	-
Glycemic control optimization (HbA1c target <7%) to reduce infection risk and improve immune response	-	ROUTINE	ROUTINE	-
Seizure safety precautions: avoid heights, swimming alone, unsupervised bathing, and operating heavy machinery until seizure-free period established	-	ROUTINE	ROUTINE	-
Adequate nutrition and hydration to support immune function and wound healing during prolonged antibiotic course	-	ROUTINE	ROUTINE	-
Cognitive rehabilitation if residual deficits present; memory strategies and organizational tools for frontal/temporal lobe involvement	-	ROUTINE	ROUTINE	-
Screen for hereditary hemorrhagic telangiectasia (HHT) if pulmonary AVM identified as source (autosomal dominant; genetic testing and family screening)	-	ROUTINE	ROUTINE	-
Regular dental hygiene and preventive care to reduce odontogenic infection risk (professional cleaning every 6 months; treat cavities promptly)	-	-	ROUTINE	-
Avoid immunosuppressive medications unless medically necessary; discuss risks with prescribing physician if immunosuppression required	-	ROUTINE	ROUTINE	-
Gradual return to work and daily activities with accommodations as needed; fatigue is common during prolonged antibiotic treatment	-	-	ROUTINE	-
Mental health support for depression and anxiety which are common during prolonged treatment and recovery from brain abscess	-	ROUTINE	ROUTINE	-

═══════════════════════════════════════════════════════════════ SECTION B: REFERENCE (Expand as Needed) ═══════════════════════════════════════════════════════════════

5. DIFFERENTIAL DIAGNOSIS

Alternative Diagnosis	Key Distinguishing Features	Tests to Differentiate
High-grade glioma (GBM)	Irregular thick ring enhancement; no DWI restriction centrally (tumor necrosis shows facilitated diffusion); older age; no fever; progressive over weeks	MRI DWI/ADC (key differentiator: tumor = no restriction; abscess = restricted diffusion); MR spectroscopy (choline peak in tumor); biopsy if uncertain
Brain metastasis	Multiple lesions at gray-white junction; known primary malignancy; ring-enhancing; no DWI restriction; no fever	MRI DWI (no restriction); CT chest/abdomen/pelvis for primary; biopsy
Cerebral toxoplasmosis	HIV/AIDS with CD4 <100; multiple ring-enhancing lesions in basal ganglia; positive Toxoplasma IgG; responds to empiric therapy	Toxoplasma IgG (>95% positive); CD4 count; empiric treatment trial (clinical and radiographic improvement in 2 weeks); biopsy if no response
Primary CNS lymphoma	Immunocompromised or immunocompetent; periventricular enhancing mass; homogeneous enhancement (vs. ring); restricted DWI	MRI (homogeneous enhancement pattern); CSF cytology; EBV PCR in CSF (HIV-related); stereotactic biopsy (definitive); avoid steroids before biopsy
Subdural empyema	Extra-axial collection; post-sinusitis/otitis; crescent-shaped enhancement; rapid clinical deterioration; seizures common	MRI with contrast (extra-axial crescentic collection with DWI restriction); CT with contrast
Tumefactive MS	Young patient; large demyelinating lesion with incomplete ring enhancement (open ring sign); less mass effect for size; white matter location	MRI (open ring enhancement; leading edge enhancement); CSF oligoclonal bands; MS-specific antibodies; biopsy if uncertain
Cerebral infarction with hemorrhagic transformation	Acute onset; vascular territory distribution; no fever initially; peripheral enhancement 1-2 weeks post-stroke can mimic abscess	Clinical history; MRI DWI pattern (vascular territory); CTA/MRA; timing of enhancement
Radiation necrosis	History of prior cranial radiation; ring-enhancing lesion in radiation field; months to years post-treatment	MR spectroscopy (lipid/lactate without choline); PET-CT (hypometabolic vs. hypermetabolic in tumor); perfusion MRI (low rCBV); biopsy
Neurocysticercosis	Endemic area exposure; ring-enhancing lesions with scolex (eccentric dot); seizures; calcified lesions; minimal edema relative to size	MRI (scolex visible as dot within cyst); serum/CSF cysticercosis antibodies; CT (calcifications); travel history
Tuberculoma	Endemic area; immunocompromised; ring-enhancing or solid nodular lesion; conglomerate lesions; basilar meningeal enhancement	AFB culture; TB PCR; QuantiFERON; chest imaging; biopsy with granulomatous inflammation; response to anti-TB therapy
Fungal granuloma (Aspergillus, Mucor)	Immunocompromised; transplant; neutropenic; angioinvasive pattern with hemorrhage; rapid progression	Galactomannan; beta-D-glucan; tissue biopsy with septate vs. non-septate hyphae; culture
Resolving hematoma (subacute-chronic)	History of trauma or anticoagulation; ring enhancement on subacute hematoma can mimic abscess; no DWI restriction; evolving signal characteristics on MRI	MRI signal evolution (T1 bright subacute blood); no DWI restriction; clinical history of trauma/anticoagulation; follow-up imaging
Demyelinating disease (tumefactive MS, ADEM)	Young patient; open ring enhancement (incomplete ring); less mass effect for lesion size; white matter location; may have other MS lesions	MRI (incomplete ring enhancement); CSF oligoclonal bands; prior episodes; brain biopsy if uncertain

6. MONITORING PARAMETERS

Parameter	ED	HOSP	OPD	ICU	Frequency	Target/Threshold	Action if Abnormal
Neurologic exam (GCS, pupils, motor, speech)	STAT	STAT	ROUTINE	STAT	q1h x 24h post-op or post-diagnosis, then q2-4h; OPD: each visit	Stable or improving GCS; no new focal deficits	If declining: STAT CT; neurosurgery reassessment; ICP management; repeat aspiration if re-accumulation
Temperature	STAT	STAT	ROUTINE	STAT	q4h (q1h if febrile)	Afebrile within 1-2 weeks of appropriate antibiotics + surgery	If persistent fever >2 weeks: repeat imaging; reassess antibiotics; evaluate for new source; consider aspiration failure
CBC with differential	STAT	ROUTINE	ROUTINE	STAT	Daily x 3 then twice weekly inpatient; weekly outpatient during IV antibiotics	Normalizing WBC; stable hemoglobin; platelets >100K	If new leukocytosis: repeat imaging; blood cultures; reassess antibiotic coverage
CRP	STAT	ROUTINE	ROUTINE	STAT	Twice weekly inpatient; weekly outpatient	Declining trend; normalize by 4-6 weeks	If rising: treatment failure; repeat imaging; reassess
ESR	-	ROUTINE	ROUTINE	ROUTINE	Weekly inpatient; every 2 weeks outpatient	Declining trend (slower to normalize than CRP; may take 6-8 weeks)	If not declining by week 3-4: reassess treatment; repeat imaging
Renal function (BUN, Cr)	STAT	ROUTINE	ROUTINE	STAT	Daily if on vancomycin; twice weekly otherwise; weekly outpatient	Stable creatinine	If rising: adjust vancomycin dose; increase hydration; consider alternative agents
Vancomycin trough/AUC (if applicable)	-	ROUTINE	ROUTINE	ROUTINE	Before 4th dose then q48-72h until stable; weekly outpatient	Trough 15-20 ug/mL or AUC/MIC 400-600	Adjust dosing; pharmacy consult
LFTs (if on metronidazole)	-	ROUTINE	ROUTINE	ROUTINE	Weekly during treatment; biweekly outpatient	Normal; no hepatotoxicity	If elevated >3x ULN: reassess metronidazole; consider dose reduction or discontinuation
Serial MRI brain with contrast	-	ROUTINE	ROUTINE	ROUTINE	At 1-2 weeks, 4 weeks, 6-8 weeks during treatment; then q2-3 months until complete resolution	Decreasing abscess size; reduced ring enhancement; reduced edema; no new lesions	If enlarging: surgical re-intervention; reassess antibiotic regimen; consider aspiration/excision
Serum sodium	STAT	ROUTINE	-	STAT	q6-12h x 48h then daily; especially if on mannitol or hypertonic saline	135-145 mEq/L	If <130: SIADH evaluation; fluid restriction; if <120: 3% saline
Seizure monitoring (clinical + EEG)	STAT	STAT	ROUTINE	STAT	Clinical: continuous in ICU; EEG if altered consciousness; OPD: seizure diary	No seizure activity	If seizures: optimize AED levels; add second agent; continuous EEG monitoring
PICC line site (outpatient)	-	-	ROUTINE	-	Daily patient self-check; weekly nursing assessment	No signs of infection, thrombosis, or malfunction	Redness/drainage: blood cultures; line removal if infected; swelling: DVT ultrasound
ICP (if EVD in place)	-	-	-	STAT	Continuous	ICP <22 mmHg; CPP 60-70 mmHg	Tiered ICP management: CSF drainage, osmotherapy, sedation, surgical decompression

7. DISPOSITION CRITERIA

Disposition	Criteria
Discharge home (with OPAT)	Clinically improving; afebrile >=48h; neurologically stable; abscess decreasing on serial imaging; oral intake adequate; reliable IV access (PICC) in place; OPAT service arranged; able to self-administer or has caregiver for home IV antibiotics; follow-up with ID and neurosurgery confirmed; seizure-free on AEDs
Admit to floor (monitored)	Stable neurologic exam (GCS >=13); no respiratory compromise; no signs of elevated ICP; abscess <2.5 cm being treated medically; post-aspiration with stable imaging; seizures controlled on medication
Admit to ICU / Neuro-ICU	GCS <13 or declining; significant mass effect or midline shift; post-craniotomy (first 24h); signs of elevated ICP; herniation syndrome; multiple abscesses with significant edema; refractory seizures or status epilepticus; intraventricular rupture (ventriculitis); hemodynamic instability; need for ICP monitoring (EVD)
Transfer to higher level	Need for neurosurgery not available at current facility; need for stereotactic aspiration capability; need for neuro-ICU expertise; need for continuous EEG not available
Inpatient rehabilitation	Moderate-severe focal deficits (hemiparesis, aphasia, cognitive impairment) after abscess treatment; able to participate in 3h/day therapy

8. EVIDENCE & REFERENCES

Recommendation	Evidence Level	Source
Empiric ceftriaxone + metronidazole +/- vancomycin for brain abscess	Class I, Level B	Brouwer et al. Clin Microbiol Rev 2014 — comprehensive review of brain abscess management
MRI with DWI to distinguish abscess from tumor (restricted diffusion = abscess)	Class I, Level A	Reddy et al. AJNR 2006 — DWI specificity ~95% for abscess vs. necrotic tumor
Stereotactic aspiration for abscesses >2.5 cm	Class IIa, Level B	Mamelak et al. Neurosurgery 1995 — CT-guided aspiration outcomes and indications
Total duration of IV antibiotics 6-8 weeks	Class I, Level B	Brouwer et al. Clin Microbiol Rev 2014; Helweg-Larsen et al. Clin Microbiol Infect 2012
Seizure prophylaxis for supratentorial brain abscess	Class IIa, Level C	Lv et al. World Neurosurg 2019 — seizure incidence 25-50% in brain abscess; prophylaxis widely practiced
Dexamethasone only for significant mass effect (not routine)	Class IIb, Level C	Brouwer et al. Clin Microbiol Rev 2014 — steroids may impair capsule formation and reduce antibiotic penetration; use only when necessary
Surgical excision for posterior fossa abscess	Class IIa, Level B	Muzumdar et al. J Neurosurg 2011 — posterior fossa abscesses have higher morbidity due to brainstem compression and hydrocephalus
Pyrimethamine + sulfadiazine for Toxoplasma abscess	Class I, Level A	IDSA Guidelines — Kaplan et al. MMWR 2009 — standard treatment for CNS toxoplasmosis in HIV
Voriconazole first-line for Aspergillus brain abscess	Class I, Level A	IDSA Aspergillosis Guidelines — Patterson et al. CID 2016
MR spectroscopy to differentiate abscess vs. tumor	Class IIa, Level B	Lai et al. AJNR 2002 — amino acid peaks and succinate specific for abscess
Serial imaging to monitor treatment response	Class I, Level B	Expert consensus; imaging at 1-2 week intervals during treatment; abscess should decrease in size by 2-4 weeks
Source identification and control (dental, otogenic, sinus)	Class I, Level B	Brouwer et al. Clin Microbiol Rev 2014 — source control essential to prevent recurrence; dental source in 25-30%
Metronidazole for anaerobic coverage with excellent CNS penetration	Class I, Level B	Ingham et al. J Antimicrob Chemother 1977; virtually 100% oral bioavailability allows early PO switch
Endocarditis screening in brain abscess with S. aureus bacteremia	Class I, Level A	AHA Endocarditis Guidelines — Baddour et al. Circulation 2015
LP generally contraindicated in brain abscess due to herniation risk	Class I, Level B	Expert consensus; mass effect from abscess creates herniation risk with CSF drainage
Craniotomy for multiloculated, posterior fossa, or fungal abscesses	Class IIa, Level B	Menon et al. J Clin Neurosci 2008 — excision preferred when aspiration unlikely to be curative
EVD for intraventricular rupture with ventriculitis	Class IIa, Level C	Brouwer et al. Clin Microbiol Rev 2014 — intraventricular rupture carries 80-100% mortality without intervention

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CHANGE LOG

v1.1 (January 30, 2026) - Standardized all structured dosing fields to 4-field :: format (dose :: route :: frequency :: instructions) across Sections 3A, 3B, 3C - Split Pyrimethamine + Sulfadiazine combined row into individual medication rows per style guide (one drug per row) - Added ICU column to Section 4B (Patient Instructions) and Section 4C (Lifestyle & Prevention) for consistent 4-venue coverage - Fixed section dividers from ASCII === to Unicode box-drawing characters - Standardized Pneumatic compression devices route and dosing format - Renamed Phenytoin/Fosphenytoin to Fosphenytoin for clarity - Added REVISED date to header metadata - Updated version to v1.1

v1.0 (January 30, 2026) - Initial template creation - Comprehensive 8-section format covering brain abscess diagnosis, antimicrobial therapy, surgical management, and follow-up - Empiric antibiotic regimen: ceftriaxone + metronidazole +/- vancomycin - Surgical decision-making: aspiration vs. excision criteria - Special populations: Toxoplasma, Nocardia, Aspergillus, Mucormycosis - Serial imaging protocol for treatment monitoring - Source identification and control recommendations - Seizure prophylaxis and ICP management - OPAT discharge planning for 6-8 week IV course

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APPENDIX A: CLASSIC PRESENTATION AND RED FLAGS

Feature	Details
Classic triad	Headache (70%), fever (50%), focal neurologic deficit (50%); full triad present in <50%
Most common symptom	Headache (70-80%) — often progressive over days to weeks
Fever	Present in only 50% at presentation; absence does NOT exclude brain abscess
Seizures	Present at diagnosis in 25-35%; lifetime incidence 25-50%
Papilledema	Present in 25%; indicates elevated ICP
Red flags for rapid deterioration	Sudden severe headache (intraventricular rupture); rapid GCS decline; new fixed dilated pupil (herniation); meningismus (ventriculitis)
Stages	Cerebritis (days 1-9) → capsule formation (days 10-14+); capsule thinner on ventricular side (risk of rupture)

APPENDIX B: ORGANISMS BY SOURCE OF BRAIN ABSCESS

Source	Typical Location	Common Organisms	Empiric Regimen
Dental / Odontogenic (25-30%)	Frontal lobe, temporal lobe	Streptococci (S. anginosus group), Fusobacterium, Prevotella, Bacteroides, Actinomyces	Ceftriaxone + Metronidazole
Otogenic (mastoiditis, cholesteatoma) (15-20%)	Temporal lobe, cerebellum	Streptococci, Bacteroides, Pseudomonas, Proteus, anaerobes	Ceftriaxone + Metronidazole
Sinogenic (frontal sinusitis) (10-15%)	Frontal lobe	Streptococci, Haemophilus, anaerobes, Staphylococci	Ceftriaxone + Metronidazole
Hematogenous (endocarditis, lung, IVDU) (15-25%)	Multiple abscesses (MCA territory)	S. aureus, Streptococci, gram-negatives, polymicrobial	Ceftriaxone + Metronidazole + Vancomycin
Post-surgical / Post-traumatic (10-15%)	Adjacent to surgical site or skull fracture	S. aureus (MRSA), S. epidermidis, Enterobacteriaceae, Pseudomonas	Vancomycin + Ceftazidime or Meropenem
Congenital heart disease / Pulmonary AVM	Multiple (right-to-left shunt)	Streptococci, Haemophilus, anaerobes	Ceftriaxone + Metronidazole
Immunocompromised (HIV, transplant)	Variable; often deep/basal ganglia	Toxoplasma, Nocardia, Aspergillus, Mucor, Cryptococcus, Listeria	Based on suspected organism + empiric broad-spectrum
Cryptogenic (unknown source, 15-20%)	Variable	Streptococci (S. anginosus group) most common; polymicrobial	Ceftriaxone + Metronidazole + Vancomycin

APPENDIX C: SURGICAL DECISION ALGORITHM

Clinical Scenario	Recommended Approach	Rationale
Abscess <2.5 cm, early cerebritis	Medical management alone (antibiotics only)	Small abscesses and cerebritis may resolve with antibiotics alone; aspiration technically difficult
Abscess >2.5 cm, accessible location	Stereotactic aspiration + antibiotics	Standard approach; less invasive than craniotomy; culture-directed therapy; may need repeat aspiration in 20-30%
Multiloculated abscess	Craniotomy with excision	Aspiration ineffective for septated collections; excision provides definitive drainage
Posterior fossa abscess	Craniotomy with excision (preferred)	High risk of brainstem compression and obstructive hydrocephalus; rapid decompression required
Fungal abscess (Aspergillus, Mucor)	Craniotomy with excision + antifungals	Poor antifungal penetration into abscess; surgical debridement critical
Traumatic abscess with foreign body	Craniotomy with excision + foreign body removal	Foreign body prevents resolution; source of persistent infection
Deep-seated (thalamus, brainstem)	Medical management or stereotactic aspiration if enlarging	Surgical risk outweighs benefit for open excision; stereotactic aspiration if accessible
Failed aspiration (re-accumulation x2)	Craniotomy with excision	Repeated aspiration failure indicates need for definitive surgical treatment
Intraventricular rupture	EVD placement + IV antibiotics + intrathecal antibiotics (consider)	Emergency; mortality 80-100% without intervention; CSF diversion critical

APPENDIX D: ANTIBIOTIC DURATION GUIDE

Scenario	IV Duration	Total Duration	Notes
Standard brain abscess (post-aspiration)	6-8 weeks IV	6-8 weeks	Serial imaging to confirm resolution
Medical management only (small abscess)	6-8 weeks IV	8-12 weeks	May need longer due to lack of surgical drainage; close imaging follow-up
Post-excision (complete removal)	4-6 weeks IV	4-6 weeks	Shorter course acceptable with confirmed complete excision
Nocardia brain abscess	6-8 weeks IV then PO	6-12 months total	Long-term oral therapy (TMP-SMX) essential; high relapse rate
Toxoplasma brain abscess (HIV)	6 weeks induction	Lifelong maintenance	Maintenance until immune reconstitution (CD4 >200 for 6 months on ART)
Fungal abscess (Aspergillus)	4-6 weeks IV	6-12 months total	Transition to oral voriconazole; duration guided by imaging
Actinomyces brain abscess	4-6 weeks IV	6-12 months PO	Prolonged oral penicillin/amoxicillin after IV induction