Recognizing Symptoms and Emergency Signs

Most brain aneurysms do not cause any symptoms until they rupture or grow large enough to press on surrounding nerves. Understanding the difference between an incidental symptom, a warning sign, and a true medical emergency is critical. If a rupture occurs, it is a life-threatening emergency that requires immediate medical intervention.

The Emergency: Ruptured Aneurysm

A ruptured aneurysm causes blood to leak into the space around the brain, a condition called a subarachnoid hemorrhage (SAH) ^[1]. This is a critical medical emergency. If you or someone else experiences the following symptoms, call emergency services (911) immediately. Do not drive yourself.

• Thunderclap Headache: This is the hallmark sign. It is often described as the “worst headache of your life.” Unlike a typical headache that builds slowly, a thunderclap headache reaches its peak intensity within 60 seconds ^[1][2].
• Sudden Neurological Deficits: This includes new one-sided weakness or numbness, facial droop, trouble speaking, or sudden severe vision loss ^[1].
• Nausea and Vomiting: Severe, sudden vomiting often accompanies the onset of the headache ^[3].
• Neck Stiffness: The presence of blood around the brain can cause the neck to become painful and rigid, making it difficult to touch your chin to your chest ^[1].
• Loss of Consciousness or Seizure: A person may become severely confused, faint (syncope), have a seizure, or become completely unconscious ^[1][3].

The Warning: Sentinel Headaches

In some cases, a major rupture is preceded by a “warning leak” known as a sentinel headache ^[4][5]. These can occur days or even weeks before a larger bleed ^[5].

A sentinel headache is also sudden and severe, but it may not be accompanied by the other emergency symptoms listed above ^[6]. Because it may improve or resolve on its own, many people mistakenly dismiss it as a bad migraine. However, a sudden, severe, and “new” type of headache should always be evaluated by a doctor immediately in an emergency setting ^[7][6].

Important: You cannot reliably diagnose or rule out an aneurysm rupture by comparing a current headache to ones you have had in the past. Any sudden-onset headache that reaches peak intensity in seconds to a minute requires urgent assessment, even if it feels “familiar” or eventually improves ^[8].

Symptoms of Unruptured Aneurysms

Most unruptured aneurysms are asymptomatic (they cause no symptoms) and are found incidentally during scans for other issues ^[9]. However, if an aneurysm is large or located near sensitive structures, it can cause “mass effect”—physically pressing on brain tissue or nerves ^[10].

• Cranial Nerve Palsy: A common sign of pressure is third-nerve palsy, which can cause a sudden drooping eyelid, a dilated pupil, or double vision ^[10][11]. Note: The sudden onset of a painful drooping eyelid or double vision requires emergency assessment, as it can indicate an aneurysm is expanding or preparing to rupture.
• Visual Disturbances: Pressure on the optic nerves can cause blurred vision or loss of vision in specific areas ^[9].
• Localized Pain: You may feel a steady, aching pain located specifically behind or above one eye ^[12].
• Other Signs: In rare cases, a large unruptured aneurysm can cause seizures or localized weakness if it presses on the brain’s motor areas ^[13].

Many patients found to have an aneurysm report a history of headaches, but studies show that in many cases, the everyday headache and the unruptured aneurysm are unrelated ^[14][15]. However, any headache that is unusually severe, sudden, or accompanied by new neurological changes requires emergency medical evaluation ^[1].