Patient-focused guidance

Symptoms

Most intracranial aneurysms cause no symptoms until they leak or rupture. A minority—especially large or giant aneurysms—can cause symptoms from pressure on nearby nerves or brain tissue.

Emergency warning: A sudden, severe “worst headache of life”, fainting, seizure, new neurological deficit, or rapidly worsening symptoms can indicate subarachnoid haemorrhage. Call your local emergency number immediately.

1) Symptoms from an unruptured aneurysm

Most people with an unruptured aneurysm feel completely well. When symptoms occur, it is usually because the aneurysm is large, growing, or located where it compresses nearby structures.

Typical “mass effect” symptoms (more common with large/giant aneurysms)

  • Headache (new, persistent, or localised)
  • Visual symptoms: blurred vision, double vision, loss of part of the visual field
  • Eye movement problems (e.g., new double vision)
  • Drooping eyelid (ptosis) or a new enlarged pupil (3rd nerve palsy)
  • Facial pain or numbness (depending on location)
  • Seizure or focal neurological symptoms (less common)

These symptoms are not specific to aneurysm. They should prompt a clinical review, especially if sudden or worsening.

What to do

  • If symptoms are new, rapidly worsening, or severe, seek urgent medical review.
  • If symptoms are mild but persistent, arrange a prompt assessment (GP/primary care or neurology).
  • If you already have a known aneurysm, inform your treating team—growth or new symptoms may change management.

If you have sudden severe headache or neurological symptoms, treat this as an emergency (see below).

2) Symptoms of a “sentinel” leak

A small leak can cause a limited subarachnoid bleed before a larger rupture. This is sometimes called a sentinel headache. Not everyone has a warning leak, but when it occurs it is clinically important because a major rupture can follow within hours to days.

Common features

  • Sudden, severe headache that peaks quickly (often minutes)
  • Headache that feels different from prior headaches/migraines
  • Neck stiffness or pain
  • Nausea/vomiting
  • Light sensitivity (photophobia)

A normal-looking person can still have a serious bleed. If the history sounds like a thunderclap headache, urgent evaluation is warranted even if symptoms partially improve.

3) Symptoms of rupture (aneurysmal subarachnoid haemorrhage)

Classic presentation

  • Sudden “thunderclap” headache (often described as the worst ever)
  • Collapse or fainting
  • Seizure
  • Vomiting
  • Neck stiffness, photophobia
  • Confusion, reduced consciousness
  • Focal neurological deficit (weakness, speech difficulty, vision loss)

What to do immediately

  1. Call emergency services now. Do not drive yourself.
  2. If safe, lie flat and stay still; avoid exertion.
  3. Note the time symptoms started (clinicians need this).
  4. Do not take aspirin/NSAIDs for the headache unless a clinician advises (bleeding risk).
  5. If the person is unconscious: place in the recovery position and start CPR if not breathing normally.

Fast transport to a hospital with CT scanning and neurovascular capability can be life‑saving.

Related pages:

Where do emergency numbers fit?

This site cannot know your local emergency number. If you travel, consider storing country-specific numbers in your phone (or using services like 112 where applicable). In Thailand, the general emergency number is commonly 1669 (medical).

Confirm local numbers for your location; they can vary by region and service.