Neurology · Year 3 · from Neurology

Case 2: Brain Abscess

Patient Demographics

  • Age: 52 years
  • Sex: Male
  • Occupation: Construction worker

Chief Complaint

"Severe headache and weakness on my right side for 5 days."

History of Present Illness

The patient presents with a 2-week history of progressively worsening headache, initially generalized but now localized to the left frontotemporal region. Over the past 5 days, he has developed weakness of his right arm and leg and has had difficulty speaking clearly. He has had low-grade fevers (up to 38.3C) and night sweats for 3 weeks. He has also noticed nausea and has vomited twice today. His wife reports he has been "not himself" with slowed thinking. His medical history includes poorly controlled type 2 diabetes (HbA1c 9.8%) and he had a dental abscess requiring extraction 6 weeks ago.

Neurological Examination Findings

Vital Signs:

  • Temperature: 37.9C (100.2F)
  • HR: 88, BP: 148/92, RR: 16

Mental Status Examination:

  • Alert but slow to respond
  • Oriented to person only
  • Impaired concentration
  • Mild expressive difficulties

Cranial Nerves:

  • Pupils equal and reactive
  • Papilledema on fundoscopy - blurred disc margins bilaterally
  • Right central facial droop (forehead spared)

Motor Examination:

  • Right upper extremity: 3/5 (deltoid, biceps, triceps, grip)
  • Right lower extremity: 4/5 (hip flexion, knee extension, ankle dorsiflexion)
  • Left side: 5/5 throughout
  • Increased tone right side

Sensory Examination:

  • Decreased sensation right arm and leg to light touch

Reflexes:

  • Right side: 3+ biceps, triceps, brachioradialis, patellar, Achilles
  • Left side: 2+
  • Right Babinski: Extensor (upgoing toe)
  • Left plantar: Flexor

Coordination:

  • Cannot assess right side due to weakness
  • Left side: Normal finger-to-nose

Gait:

  • Unable to ambulate safely - right hemiparetic gait

Risk Factors Identified

  1. Diabetes mellitus - poorly controlled (immunocompromised state)
  2. Recent dental infection - potential source of hematogenous spread
  3. Contiguous spread risk factors: None identified

Neuro Workup

Laboratory Studies:

  • WBC: 15,200 with left shift (80% neutrophils)
  • ESR: 78 mm/hr (elevated)
  • CRP: 145 mg/L (elevated)
  • Blood glucose: 285 mg/dL
  • Blood cultures: Drawn (pending)
  • HbA1c: 9.8%

CT Head without Contrast (initial):

  • Left frontal hypodense lesion with surrounding edema
  • Mass effect with midline shift 6mm to right
  • Effacement of left lateral ventricle

MRI Brain with Contrast:

  • 3.5 cm ring-enhancing lesion in left frontal lobe
  • Smooth, thin-walled enhancing rim (thinner on ventricular side)
  • Central T2 hyperintensity (necrotic center)
  • Extensive surrounding vasogenic edema
  • Restricted diffusion on DWI/ADC - bright on DWI, dark on ADC
  • Key distinguishing feature from necrotic tumor
  • Midline shift with subfalcine herniation

Lumbar Puncture:

  • CONTRAINDICATED due to significant mass effect and herniation risk

CT Chest/Abdomen/Pelvis:

  • No evidence of pulmonary abscess or other source

Echocardiogram:

  • No vegetations (ruling out endocarditis)

Diagnosis

Brain Abscess - likely odontogenic source (post-dental extraction)

  • Most likely organisms: Streptococcus species (viridans group), anaerobes (Bacteroides, Peptostreptococcus, Fusobacterium)

Management

Immediate Medical Treatment:

  1. Empiric IV Antibiotics (started immediately):
  • Ceftriaxone 2g IV q12h (covers streptococci, gram-negatives)
  • Metronidazole 500mg IV q8h (covers anaerobes)
  • Vancomycin 15-20 mg/kg IV q8-12h (covers MRSA - added given immunocompromised)
  • Total duration: 6-8 weeks IV antibiotics
  1. Cerebral Edema Management:
  • Dexamethasone 10mg IV load, then 4mg q6h
  • Head of bed elevated 30 degrees
  • Avoid hypercarbia
  1. Seizure Prophylaxis:
  • Levetiracetam 500mg IV BID (supratentorial lesion)
  1. Glucose Control:
  • Insulin infusion to target glucose 140-180 mg/dL

Surgical Treatment:

  • Neurosurgery consulted emergently
  • Stereotactic aspiration performed - both diagnostic and therapeutic
  • Purulent material obtained
  • Gram stain: Gram-positive cocci in chains, gram-negative rods
  • Culture: Streptococcus intermedius, Fusobacterium nucleatum
  • Antibiotics narrowed based on culture/sensitivities

Indications for Surgery Met:

  • Abscess >2.5 cm diameter
  • Significant mass effect
  • Neurological deterioration
  • Accessible location

Follow-up:

  • Serial MRI every 2 weeks to monitor resolution
  • Continue antibiotics until abscess cavity resolved or stable residual
  • Long-term antiepileptic drugs if seizures occur
  • Dental evaluation and treatment of any remaining dental disease

Prognosis:

  • Mortality: 5-15% with modern treatment
  • Factors associated with poor outcome: Poor GCS at presentation, rapid progression, intraventricular rupture, multiple abscesses
  • Most patients have good functional recovery with early treatment

Clinical Image

Image Description: Contrast-enhanced MRI showing a ring-enhancing brain abscess with smooth, thin walls and surrounding vasogenic edema. The central cavity shows restricted diffusion, distinguishing abscess from necrotic tumor.

Attribution: Image from Wikimedia Commons. Licensed under CC BY-SA 3.0. Source: https://commons.wikimedia.org/wiki/File:Contrast-enhanced_MRI_of_a_brain_abscess.jpg

Key Teaching Points

Herpes Simplex Encephalitis

  1. Most common cause of sporadic viral encephalitis
  2. Temporal lobe predilection - behavioral changes, aphasia, seizures
  3. Start acyclovir empirically - do not wait for PCR results
  4. CSF shows lymphocytic pleocytosis, may have RBCs
  5. MRI more sensitive than CT - T2/FLAIR hyperintensity in temporal lobes
  6. Early treatment dramatically improves survival

Brain Abscess

  1. Classic triad: Headache (most common), fever (~50%), focal deficit (~50%)
  2. Ring enhancement with restricted diffusion distinguishes from tumor
  3. Common sources: Dental, sinusitis, otitis, endocarditis, hematogenous
  4. Empiric antibiotics: Cover streptococci, anaerobes, +/- staph
  5. Surgery for abscess >2.5 cm or significant mass effect
  6. LP contraindicated with mass effect
  7. Duration: 6-8 weeks IV antibiotics

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