Neuro: Subarachnoid Haemorrhage & Aneurysms for MRCP Part 1

TL;DR

Subarachnoid haemorrhage (SAH) from ruptured intracranial aneurysms is a high-yield neurology topic for MRCP Part 1. Candidates must recognise the classic thunderclap headache, know the CT → lumbar puncture diagnostic pathway, and remember complications such as vasospasm treated with nimodipine. Understanding the core principles of Neuro: Subarachnoid Hemorrhage & Aneurysms can help secure straightforward marks in neurology questions.

Why this matters

Neurological emergencies frequently appear in MRCP Part 1, particularly those where clinical recognition and investigation strategy are key. Subarachnoid haemorrhage represents a classic example.

Questions typically test:

• Recognition of sudden severe headache

• Appropriate diagnostic investigations

• Complications such as cerebral vasospasm

• Key risk factors and aneurysm locations

Because these patterns repeat regularly in exams, mastering SAH can quickly improve neurology performance.

For a structured overview of the examination and syllabus distribution, see the MRCP Part 1 overview.

Core Sections

1. What is Subarachnoid Haemorrhage?

Subarachnoid haemorrhage refers to bleeding into the subarachnoid space between the arachnoid mater and pia mater.

Major causes

Cause	Approximate proportion	Key point
Ruptured berry aneurysm	~80–85%	Most common non-traumatic cause
Arteriovenous malformation	~5–10%	Often presents in younger patients
Trauma	Variable	Most common overall cause of SAH
Perimesencephalic haemorrhage	Small proportion	Usually benign course

For MRCP Part 1, questions overwhelmingly focus on aneurysmal SAH.

2. Intracranial Aneurysms: Key Facts

Berry aneurysms develop at arterial bifurcations within the Circle of Willis due to vessel wall weakness.

Common aneurysm locations

1. Anterior communicating artery (most common)

2. Posterior communicating artery

3. Middle cerebral artery bifurcation

4. Basilar artery tip

5. Internal carotid artery

Important risk factors

• Hypertension

• Cigarette smoking

• Autosomal dominant polycystic kidney disease

• Connective tissue disorders (e.g., Ehlers–Danlos syndrome)

• Family history of aneurysms

These associations frequently appear in single-best-answer MRCP questions.

3. Classic Presentation: Thunderclap Headache

The hallmark symptom of SAH is sudden onset severe headache.

Patients commonly describe:

“The worst headache of my life.”

Other features may include:

• Vomiting

• Neck stiffness

• Photophobia

• Reduced consciousness

• Seizures

Neurological signs

Key exam findings include:

• Meningism (neck stiffness)

• Reduced level of consciousness

• Cranial nerve palsies

A particularly important association is:

Posterior communicating artery aneurysm → third cranial nerve palsy

Features include ptosis, diplopia, and a dilated pupil.

4. Diagnostic Approach

Recognising the correct investigation pathway is crucial for MRCP.

Stepwise approach

1. Urgent non-contrast CT brain

2. If CT negative but suspicion remains → lumbar puncture

3. Confirm aneurysm using CT angiography or MR angiography

Lumbar puncture finding

The most important CSF finding is xanthochromia, caused by haemoglobin breakdown.

Important timing:

• Appears approximately 12 hours after haemorrhage

• Persists for several days

This timing frequently appears in MRCP exam questions.

5. Major Complications of SAH

Complications are heavily tested.

Complication	Timing	Key exam point
Rebleeding	First 24–48 hours	High mortality
Cerebral vasospasm	Day 3–14	Causes delayed cerebral ischaemia
Hydrocephalus	Early	Due to impaired CSF absorption
Hyponatraemia	Days 4–10	Often due to SIADH
Seizures	Early	Cortical irritation

Cerebral vasospasm

Cerebral vasospasm is the most tested complication.

Key facts:

• Occurs 3–14 days after haemorrhage

• Leads to delayed neurological deficit

• Prevented with nimodipine

6. Management Principles

Management typically occurs in specialised neurosurgical units.

Initial management

• Stabilise airway and circulation

• Control blood pressure

• Provide analgesia

• Prevent complications

Medical therapy

Nimodipine

• Calcium channel blocker

• Reduces risk of delayed cerebral ischaemia

• Standard therapy following aneurysmal SAH

Definitive aneurysm treatment

Two approaches are used:

• Endovascular coiling

• Surgical clipping

Modern practice often favours coiling because it is less invasive.

Clinical guidance can be reviewed in NICE guidelines on subarachnoid haemorrhage management:https://www.nice.org.uk/guidance

7. Prognostic Scoring Systems

Two grading systems occasionally appear in MRCP questions.

Hunt and Hess Scale

Grades SAH severity based on:

• Clinical condition

• Neurological deficit

World Federation of Neurological Surgeons (WFNS) Scale

Uses:

• Glasgow Coma Scale

• Presence of neurological deficit

Lower scores correlate with better prognosis.

8. High-Yield Points for MRCP Part 1

Memorising these facts can answer many exam questions.

1. SAH most commonly results from ruptured berry aneurysm.

2. Anterior communicating artery is the most common aneurysm site.

3. Thunderclap headache is the classic presentation.

4. Non-contrast CT brain is the first investigation.

5. If CT is negative → lumbar puncture for xanthochromia.

6. Vasospasm occurs 3–14 days after SAH.

7. Nimodipine reduces vasospasm risk.

8. Posterior communicating aneurysm can cause CN III palsy.

9. Hypertension and smoking are major risk factors.

10. Definitive treatment is coiling or clipping.

For exam-style practice questions covering these topics, try the Free MRCP MCQs.

You can also simulate exam conditions using the MRCP mock tests.

Practical Example (Mini-Case)

A 54-year-old woman presents with a sudden severe headache while exercising. She reports it as the worst headache of her life and develops vomiting and photophobia. CT brain confirms subarachnoid haemorrhage.

Which medication should be started to reduce the risk of delayed cerebral ischaemia?

A. VerapamilB. NimodipineC. MannitolD. AspirinE. Phenytoin

Answer: B. Nimodipine

Explanation

Delayed neurological deficits after SAH are commonly due to cerebral vasospasm. Nimodipine reduces the risk of vasospasm and improves outcomes, making it the standard medical therapy following aneurysmal SAH.

Common Pitfalls (Exam Traps)

• Assuming CT alone rules out SAH; lumbar puncture may still be required.

• Forgetting xanthochromia timing (~12 hours).

• Confusing vasospasm timing with early complications.

• Missing CN III palsy caused by posterior communicating aneurysm.

• Assuming nimodipine treats rebleeding rather than preventing vasospasm.

Avoiding these traps improves accuracy in neurology questions.

Practical Study-Tip Checklist

When revising SAH for MRCP Part 1, ensure you can:

✔ Identify aneurysm locations within the Circle of Willis✔ Recognise thunderclap headache presentations✔ Recall the CT → LP diagnostic pathway✔ Remember vasospasm timing (3–14 days)✔ Associate CN III palsy with posterior communicating aneurysm✔ Understand the role of nimodipine✔ Practise scenario-based questions regularly

A structured revision approach is outlined in the MRCP Part 1 overview.

FAQs

What is the most common cause of subarachnoid haemorrhage?

The most common non-traumatic cause is rupture of a saccular (berry) aneurysm in the Circle of Willis, particularly at the anterior communicating artery.

Why is nimodipine given after subarachnoid haemorrhage?

Nimodipine reduces the risk of cerebral vasospasm, which can cause delayed cerebral ischaemia several days after SAH.

When should lumbar puncture be performed in suspected SAH?

If CT brain is negative but suspicion remains high, lumbar puncture should be performed at least 12 hours after symptom onset to detect xanthochromia.

What is the classic symptom of SAH?

The hallmark symptom is a sudden thunderclap headache, often described as the worst headache of the patient’s life.

Which aneurysm commonly causes third nerve palsy?

A posterior communicating artery aneurysm can compress the oculomotor nerve, causing ptosis, diplopia, and pupillary dilation.

Ready to start?

Preparing effectively for MRCP Part 1 requires mastering high-yield topics and practising exam-style questions.

Start your revision with the MRCP Part 1 overview, then test your knowledge using the Free MRCP MCQs and full MRCP mock tests available at Crack Medicine.

Sources

• MRCP(UK) Examination Blueprint — https://www.mrcpuk.org

• NICE Clinical Knowledge Summaries — https://cks.nice.org.uk

• National Institute for Health and Care Excellence Guidelines — https://www.nice.org.uk

• RCP Neurology Curriculum — https://www.rcplondon.ac.uk

• Adams & Victor’s Principles of Neurology