Study guide
23.4 Acute CNS Infections (03.M)
ABIM Neurocritical Care Subspecialty Certification Exam
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 Eligibility, Practice Pathway, and the IM Training Route 1.3 Format, Scoring, Pearson VUE, and Score Reports 1.4 How to Use This Independent Study Guide
2 ICU Neurologic Exam, Cerebral Physiology, and CSF
2.1 Neurological Examination in the ICU 2.2 Cerebral Physiology, ICP, CBF, and Autoregulation 2.3 CSF Physiology
3 Core Neuropharmacology
3.1 Osmotic Agents 3.2 Anti-Seizure Drugs 3.3 Anesthetics, Sedatives, Analgesia, and Paralytics 3.4 Antihypertensives, Vasopressors, and Inotropes
4 Reperfusion Drugs, Airway, and Ventilation
4.1 Thrombolytics, Anticoagulants, and Antiplatelets 4.2 Reversal of Anticoagulation After Acute Hemorrhage 4.3 Airway Management and Tracheostomy 4.4 Mechanical Ventilation
5 Hemodynamics and Shock
5.1 Hemodynamic Monitoring 5.2 IABP, Temporary VADs, LVAD, and ECMO 5.3 Diagnosis and Management of Shock
6 Nutrition, Temperature, and ICU Prophylaxis
6.1 Nutrition (01.J) 6.2 Temperature Control (01.K) 6.3 ICU Prophylaxis, Delirium, and Early Mobility (01.L)
7 General Trauma
7.1 Emergency Evaluation of Polytrauma, Chest, and Abdominal Trauma 7.2 Long-Bone Fractures and Fat Embolism 7.3 Burns, Electrical Injury, and Hanging/Strangulation
8 Pulmonary Critical Care
8.1 Pulmonary Physiology and ARDS (01.N.1–2) 8.2 PE, Pneumonia, and Pulmonary Edema (01.N.3, 7–8) 8.3 COPD, Asthma, PAH, and Bronchoscopy Basics (01.N.4–6, 9)
9 Cardiovascular Critical Care
9.1 Cardiovascular Physiology, Stress Cardiomyopathy, ACS, and Valves 9.2 Arrhythmias and Pacing 9.3 Acute Aortic Dissection and Cardiac Ultrasound
10 Renal and Infectious Disease
10.1 AKI, RRT, and Renal Drug Dosing 10.2 Acid-Base and Electrolyte Disorders 10.3 Severe Sepsis, Septic Shock, and Infective Endocarditis 10.4 Antimicrobial Use and Infection in the Immunosuppressed
11 Endocrine and Salt-Water Disorders
11.1 Pituitary Apoplexy, DI, and Panhypopituitarism (01.R.1–4) 11.2 SIADH and Cerebral Salt Wasting (01.R.5–6) 11.3 Thyrotoxicosis, Myxedema, Adrenal Crisis, and Dysglycemia (01.R.7–9)
12 Gastrointestinal Critical Care
12.1 GI Physiology, Acute Abdomen, Bleed, Ileus, and Perforation (01.S.1–5) 12.2 Mesenteric Ischemia and Abdominal Compartment Syndrome (01.S.6–7) 12.3 Fulminant Liver Failure, Cirrhosis Decompensation, and Hepatic Dosing (01.S.8–10)
13 Hematologic Disorders
13.1 Anemia, Transfusion, Thrombocytopenia, Coagulopathy, and DIC (01.T.1–4) 13.2 VTE in the Neuro ICU (01.T.5) 13.3 Chemo/Immune, SCT, CAR-T, Sickle Cell, and TMA (01.T.6–10)
14 Neuroimaging
14.1 CT of Brain and Spine 14.2 MRI and CT/MR Perfusion 14.3 Noninvasive Angiography and Catheter Angiography
15 EEG, EMG, and CSF Analysis
15.1 EEG, Standard and Processed (02.B) 15.2 Basic EMG Interpretation (02.G) 15.3 CSF Analysis (02.H)
16 ICP, TCD, and Multimodality Monitoring
16.1 ICP Monitoring (02.C) 16.2 Transcranial Doppler (02.D) 16.3 Brain-Tissue Oxygen and Multimodality Monitoring (02.E–F)
17 Brain Death and Bedside Procedures
17.1 Brain Death Prerequisites and Clinical Exam (02.I) 17.2 Apnea Testing and Ancillary Studies (02.I) 17.3 Vascular Access, Thoracic Echo, and Lung Ultrasound (02.J–L)
18 Coma, Anoxia, and Intracranial Hypertension
18.1 Coma and Other States of Altered Consciousness (03.A) 18.2 Global Anoxia-Ischemia and Post-Resuscitation Encephalopathy (03.A.1) 18.3 Toxidromes, ICU Delirium, and Hypertensive Encephalopathy (03.A.2–4) 18.4 Intracranial Hypertension as a Disease State (03.B)
19 Acute Ischemic Stroke
19.1 IV Reperfusion Therapy (03.C.3) 19.2 Mechanical Thrombectomy Windows and Imaging Selection (03.C.3) 19.3 Malignant Hemispheric Infarction and Basilar Artery Occlusion (03.C.1–2)
20 Intraparenchymal Hemorrhage
20.1 Intracerebral Hematoma (03.D.1) 20.2 Cerebellar Hematoma (03.D.2) 20.3 Intraventricular Hemorrhage (03.D.3)
21 SAH, CVST, and Spinal Cord Infarction
21.1 Aneurysmal Subarachnoid Hemorrhage (03.E.1) 21.2 Non-Aneurysmal SAH (03.E.2) 21.3 Cerebral Venous Sinus Thrombosis (03.F) 21.4 Spinal Cord Infarction (03.G)
22 Vascular Anomalies and Traumatic Brain Injury
22.1 Unruptured Aneurysm, Cavernoma, AVM, and Dural AVF (03.H) 22.2 Diffuse Axonal Injury and Cerebral Contusions (03.I.1–2) 22.3 Epidural Hematoma, Subdural Hematoma, and Penetrating Injury (03.I.3–4, 7) 22.4 Arterial Dissection and Carotid-Cavernous Fistula (03.I.5–6)
23 Spine, Hydrocephalus, and CNS Infection
23.1 Spinal Cord Injury, Central Cord, and Neurogenic Shock (03.J) 23.2 Unstable Spine Fractures (03.K) 23.3 Hydrocephalus and CSF Diversion (03.L) 23.4 Acute CNS Infections (03.M)
24 Seizures and Neuromuscular Emergencies
24.1 Status Epilepticus and Seizures (03.N) 24.2 Guillain-Barré Syndrome (03.O.1) 24.3 Myasthenic Crisis (03.O.2) 24.4 Motor Neuron Disease, Acute Myopathies, Rhabdomyolysis, and CINM (03.O.3–6)
25 Inflammatory Disease, Neuro-Oncology, and Special Populations
25.1 Fulminant Demyelinating Diseases (03.P) 25.2 Autoimmune Encephalitis and Acute Autonomic Hyperactivity (03.Q–R) 25.3 Neuro-Oncology and Treatment Complications (03.S) 25.4 Pregnancy/Post-Partum, Post-Transplant, and Pediatric Patients (03.T–U)
26 Neurosurgical and Perioperative Complications
26.1 Postoperative Seizures, Hemorrhage, Ischemia, and Hyperperfusion (04.A, C, D, H) 26.2 Infection, CSF Leak, and Pneumocephalus (04.B, E, F) 26.3 Complications of EVD and Lumbar Drain (04.G, I)
27 Ethics, Prognostication, and Organ Donation
27.1 Communication, Decision-Makers, Advance Directives, and DNR (05.A, B, G) 27.2 Uncertainties of Prognostication and the Self-Fulfilling Prophecy (05.C) 27.3 Palliative Care, Withdrawal, Withholding, and Futility (05.D–F) 27.4 Donation After Cardiac Death and Care of the Organ Donor (05.H–I)
23.4 Acute CNS Infections (03.M)
Key Takeaways Explain This Topic AI
In suspected community bacterial meningitis, give dexamethasone immediately before or with the first antibiotic dose when pneumococcus is possible; do not wait for CSF Gram stain if that wait delays drugs.
Start intravenous acyclovir as soon as HSV encephalitis is in the differential; temporal/insular imaging and CSF PCR confirm, they do not license a delay.
Brain abscess, subdural empyema, and spinal epidural abscess are not interchangeable: empyema and spinal epidural abscess with deficit are surgical emergencies plus antibiotics.
EVD or shunt ventriculitis needs CSF sampling and hardware removal; empiric therapy is vancomycin plus an anti-pseudomonal beta-lactam (IDSA 2017).
Empiric meningitis drugs follow age and neurosurgical context; immunocompromised pathogens (Toxoplasma, Cryptococcus, and related) are covered in chapter 10.4, not by ceftriaxone alone.
Last updated: September 2026
Minutes matter more in CNS infection than in almost any other 03.M-adjacent topic. Independent ExamFinch teaching for ABIM Neurocritical Care is the community-meningitis bundle, HSV treated on suspicion, the surgical infections that antibiotics alone will not drain, and ventriculitis on an EVD. Hosts without a working immune system need extra organisms; that list lives with 10.4 Antimicrobial Use and Infection in the Immunosuppressed — point there rather than duplicating toxoplasmosis protocols here.
Community bacterial meningitis
The classic triad (fever, nuchal rigidity, altered mental status) is incomplete in many adults. Still treat empirically when the pretest probability is real. Sequence that does not delay drugs:
Two sets of blood cultures .
Dexamethasone and antibiotics immediately if LP will wait for CT.
Lumbar puncture when safe; CT first only for the IDSA-style red flags (immunocompromise, known CNS disease, new seizure, papilledema, focal deficit, moderate-to-severe impairment of consciousness).
Adjunctive dexamethasone 10 mg IV every 6 hours for 4 days (adult dosing from de Gans and van de Beek, NEJM 2002) is given 15–20 minutes before or with the first antibiotic dose. That trial showed fewer unfavorable outcomes ( 15% vs 25% ) and lower mortality ( 7% vs 15% ), with the clearest benefit in Streptococcus pneumoniae . IDSA 2004 bacterial meningitis guidance endorses dexamethasone in suspected or proven pneumococcal disease in adults. If the pathogen is later not pneumococcus (and not H. influenzae in children), stop the steroid. Do not start dexamethasone hours after antibiotics “because someone remembered.” Do not use it as routine therapy for healthcare-associated gram-negative meningitis or for septic shock from meningococcemia without meningitis — those are different inflammatory problems.
Empiric intravenous regimens are conceptual, then narrowed to MIC and CNS penetration:
Setting Typical organisms Empiric backbone (adults; local antibiogram applies)
Community, age 16–50 years Pneumococcus, meningococcus Vancomycin plus ceftriaxone 2 g every 12 hours (or cefotaxime)
Community, age >50 or cell-mediated immune defect Above plus Listeria Add ampicillin 2 g every 4 hours
Basilar skull fracture / CSF leak Pneumococcus, streptococci, H. influenzae Vancomycin plus a third-generation cephalosporin
Post-neurosurgery, penetrating trauma, or CSF shunt/EVD Staphylococci including MRSA, Cutibacterium , hospital gram-negatives including Pseudomonas Vancomycin plus cefepime, ceftazidime, or meropenem (IDSA 2017 healthcare-associated ventriculitis/meningitis)
Ceftriaxone doses used for meningitis are CNS doses , not 1 g daily community-pneumonia doses. Vancomycin is included because penicillin-nonsusceptible pneumococcus is not rare. Ampicillin is the Listeria drug; cephalosporins do not cover Listeria. After neurosurgery, ceftriaxone alone is the wrong gram-negative choice.
Droplet precautions for meningococcus until 24 hours of effective therapy. Chemoprophylaxis for close contacts is a public-health task, not an ICU afterthought.
HSV encephalitis: treat, then confirm
Herpes simplex virus (HSV-1) encephalitis is a necrotizing temporal and insular process. Personality change, fever, new seizures, and a CSF lymphocytic pleocytosis with a high protein and variable red cells should start acyclovir 10 mg/kg of ideal body weight IV every 8 hours immediately. MRI: T2/FLAIR hyperintensity in the medial temporal lobe , insula, and cingulate, often asymmetric. EEG may show periodic discharges over the temporal region. CSF HSV PCR is the confirmatory test; it can be falsely negative in the first 72 hours. A negative day-1 PCR does not stop acyclovir if the MRI and story still fit — repeat LP. Dose-adjust for GFR; early treatment changes mortality. Add bacterial coverage if you cannot exclude bacterial meningitis at the door. VZV, autoimmune encephalitis, and abscess enter the differential; they do not justify withholding the first acyclovir dose.
Abscess, subdural empyema, spinal epidural abscess
These three are all “pus near the neuraxis.” They are not the same operation.
Entity Where the pus lives Typical source First definitive move besides antibiotics
Brain abscess Parenchymal, often ring-enhancing with diffusion restriction Hematogenous (endocarditis, pulmonary shunt) or contiguous sinus/ear Stereotactic aspiration or excision if large, mass-effect, or diagnosis unclear; small, multiple abscesses may be medical after a causative organism is known
Subdural empyema Between dura and arachnoid, spreads over the convexity Sinusitis, mastoiditis, post-craniotomy Emergency surgical drainage ; antibiotics alone fail as pus layers over cortex
Spinal epidural abscess Spinal epidural space Skin/soft-tissue S. aureus , injection, endocarditis, contiguous osteomyelitis Emergency surgical decompression when there is deficit, sepsis with collection, or failure of medical therapy; MRI of the whole spine because skip lesions exist
Empiric drugs while you go to the scanner and the OR often include vancomycin plus a third-generation cephalosporin plus metronidazole for community brain abscess (staph, strep, anaerobes from sinus). Post-neurosurgical collections follow the hospital-meningitis table (vancomycin plus anti-pseudomonal beta-lactam). Spinal epidural abscess is S. aureus until proven otherwise: vancomycin plus a gram-negative agent that covers the local epidemiology, then narrow.
The classic spinal triad (back pain, fever, neurologic deficit) is often missing a piece. Do not wait for paralysis to call MRI. Once plegia is established, recovery odds collapse. That is why this is a surgical emergency plus antibiotics, not a 48-hour vancomycin trial in a ward bed.
Ventriculitis and EVD infection
An EVD is a foreign body in the ventricle. Infection risk rises with duration, breaks in the closed system, and CSF leaks at the tunnel. Fever, unexplained GCS drop, or a change in CSF appearance should trigger CSF sampling from the drain (Gram stain, culture, cell count, glucose, protein). Interpretation is messy because blood and the catheter itself inflame the fluid. Culture and a falling glucose with a rising neutrophil count still matter. Repeat sampling when the first draw is ambiguous.
IDSA 2017: remove the infected CSF drain ; if diversion is still required, replace at a new site. Infected VP shunts are fully removed and replaced by a temporary EVD, not “suppressed” in situ. Empiric intravenous therapy is vancomycin plus cefepime, ceftazidime, or meropenem . Intraventricular antibiotics are reserved for selected persistently positive cultures after removal, not as a way to leave hardware in. Chapter 26 returns to EVD technical complications (malposition, hemorrhage, overdrainage); the infection rule is already this: sample, remove, cover widely, then narrow .
Immunocompromised extras — pointer, not a second chapter
HIV with a CD4 count in the cellar, transplant recipients, and patients on high-dose steroids do not get “community meningitis plus a shrug.” Add Listeria (ampicillin) when risk is present even under age 50. Cryptococcus needs antigen testing and induction amphotericin plus flucytosine, not ceftriaxone. Toxoplasma ring lesions are pyrimethamine-based therapy after imaging, not empiric metronidazole for pyogenic abscess without a host clue. PML, CMV, endemic fungi, and nocardia live in section 10.4 . If the stem is a transplant patient with fever and a ring lesion, do not stop at the table above.
Exam traps
Holding antibiotics for a CT that is two hours away. Giving dexamethasone the next morning. Waiting for HSV PCR before acyclovir. Treating subdural empyema with 6 weeks of antibiotics and no surgeon. Sampling an EVD, leaving it in, and calling that a cure. Using 1 g of ceftriaxone daily for meningitis. Forgetting ampicillin in a 72-year-old. Forgetting vancomycin plus cefepime after a craniotomy.
In practice
A 68-year-old with fever and coma: blood cultures, dexamethasone 10 mg IV, vancomycin plus ceftriaxone plus ampicillin, then CT if needed and LP — that is community meningitis with Listeria coverage. A 34-year-old with new temporal seizures: acyclovir now, MRI and PCR in parallel. A teenager with frontal sinusitis and a rapidly spreading hemiparesis: subdural empyema, call the OR. A thoracic back-pain patient who cannot lift the legs: whole-spine MRI and a spine surgeon the same hour. An EVD day-8 fever: CSF from the drain, new catheter, vancomycin plus cefepime.