top of page
Search

Brain Abscess & Subdural Empyema

TL;DR

Brain Abscess & Subdural Empyema are high-yield neurology topics in MRCP Part 1, often tested through imaging, source of infection, and management decisions. Recognise the triad of headache, fever, and focal deficit, but remember it is frequently incomplete. CT/MRI is diagnostic, while lumbar puncture is contraindicated in raised ICP. Early antibiotics and neurosurgical referral are essential to prevent mortality.


Why this matters

Focal intracranial infections are repeatedly examined in MRCP Part 1, especially because they integrate clinical reasoning across neurology, microbiology, and radiology. Brain abscess and subdural empyema are not only life-threatening but also highly predictable exam topics.

Candidates are expected to identify risk factors, interpret imaging, and avoid dangerous errors such as performing lumbar puncture in raised intracranial pressure. For a structured preparation strategy, review the MRCP Part 1 overview.


Core sections

1. Definitions and pathology

  • Brain abscess: A focal collection of pus within the brain parenchyma

  • Subdural empyema: A collection of pus in the subdural space (between dura and arachnoid)

👉 Key concept:

  • Brain abscess = intra-axial

  • Subdural empyema = extra-axial and spreads rapidly

2. Pathogenesis and sources of infection

Understanding the source is essential for MRCP questions.

Source of Infection

Likely Organisms

Common Location

Otitis media/mastoiditis

Streptococci, anaerobes

Temporal lobe

Sinusitis

Streptococci, anaerobes

Frontal lobe / empyema

Infective endocarditis

Staphylococcus aureus

Multiple lesions

Trauma/neurosurgery

Staph aureus, Gram-negative bacilli

Variable

💡 High-yield link:

  • Frontal sinusitis → subdural empyema (classic exam association)

3. Clinical features

The classic triad:

  1. Headache

  2. Fever

  3. Focal neurological deficit

⚠️ Exam trap: Present in fewer than half of patients.

Additional features:

  • Seizures (particularly in brain abscess)

  • Altered mental status

  • Signs of raised ICP (vomiting, papilloedema)

4. Imaging – the most tested domain

First-line investigation: Contrast-enhanced CT or MRI

Key imaging findings:

  • Brain abscess → ring-enhancing lesion with surrounding oedema

  • Subdural empyema → crescent-shaped extra-axial collection

💡 Critical rule:

  • Do NOT perform lumbar puncture if raised ICP is suspected

MRI is more sensitive than CT and is often used if diagnosis is uncertain.

5. Management principles

Immediate steps:

  • Urgent intravenous antibiotics

  • Neurosurgical consultation

Empirical antibiotic regimen:

  • Ceftriaxone + metronidazole

  • Add vancomycin if Staphylococcus aureus suspected

Surgical management:

  • Brain abscess → aspiration or excision

  • Subdural empyema → urgent surgical drainage (emergency)

6. High-yield comparison table

Feature

Brain Abscess

Subdural Empyema

Location

Intra-parenchymal

Extra-axial

Progression

Gradual

Rapid

Common source

Ear infection, IE

Sinusitis

Imaging

Ring-enhancing lesion

Crescent-shaped collection

Urgency

Urgent

Emergency

7. Top 10 exam-focused revision points

  1. Ring-enhancing lesion = brain abscess until proven otherwise

  2. Sinusitis is the most common cause of subdural empyema

  3. Lumbar puncture is contraindicated in raised ICP

  4. Multiple lesions suggest haematogenous spread (e.g. endocarditis)

  5. Seizures are common presenting features

  6. MRI is more sensitive than CT

  7. Metronidazole is essential for anaerobic coverage

  8. Subdural empyema spreads rapidly across the brain surface

  9. Early neurosurgical referral improves outcomes

  10. Immunocompromised patients may have atypical infections

Medical student revising neurology topics including brain abscess and subdural empyema for MRCP Part 1 exam

Practical examples / mini-cases

Case-based MCQ

A 32-year-old man presents with fever, worsening headache, and confusion. He has a history of chronic sinusitis. Examination reveals right-sided weakness. CT scan shows a crescent-shaped extra-axial collection.

What is the most likely diagnosis?

A. Brain abscessB. Subdural empyemaC. Epidural abscessD. MeningitisE. Primary brain tumour

✅ Answer: B. Subdural empyema

Explanation:

  • Sinusitis → classic source

  • Crescent-shaped lesion → extra-axial

  • Rapid neurological deterioration → empyema

👉 This is a neurosurgical emergency requiring urgent drainage.

Practise more cases with our Free MRCP MCQs or test your readiness using a Start a mock test.


Common pitfalls (5 bullets)

  • Assuming the triad must be present

  • Performing lumbar puncture before imaging

  • Missing sinusitis as a key source

  • Confusing abscess with tumour on imaging

  • Delaying surgical referral in subdural empyema


FAQs

1. What is the hallmark imaging feature of brain abscess?

A ring-enhancing lesion with surrounding oedema on contrast imaging is the key feature tested in MRCP Part 1.

2. Why should lumbar puncture be avoided?

It can precipitate brain herniation in the presence of raised intracranial pressure or mass effect.

3. Which condition is more dangerous?

Subdural empyema progresses more rapidly and is a neurosurgical emergency.

4. What organisms are commonly involved?

Streptococci and anaerobes are common; Staphylococcus aureus is typical in haematogenous spread.

5. What is the first-line treatment?

Empirical IV antibiotics (ceftriaxone + metronidazole) and urgent neurosurgical involvement.


Ready to start?

Strengthen your performance in MRCP Part 1 by mastering high-yield topics like Brain Abscess & Subdural Empyema. Practise systematically with our Free MRCP MCQs and simulate real exam conditions using a Start a mock test. Build a complete strategy with the MRCP Part 1 overview.


Sources

 
 
 

Comments

bottom of page