Sudden Onset of Severe Headache (Thunderclap Headache)

What makes a headache a thunderclap headache?

Most headaches build over minutes to hours. A thunderclap headache:

• reaches its peak intensity within 1 minute (some definitions allow up to 5 minutes)
• is severe, often described as 10 out of 10 or the worst ever
• may come with nausea, vomiting, neck stiffness, light sensitivity or a brief loss of consciousness
• can last from hours to days

Even if it fades, the speed of onset is what matters. Around 1 in 4 people with a bleed from an aneurysm have a smaller "sentinel" headache days or weeks before a major bleed, so a single sudden severe headache should never be dismissed.

Causes of sudden severe headache

Subarachnoid hemorrhage

A subarachnoid hemorrhage is bleeding into the space around the brain. Most are caused by a ruptured brain aneurysm, a weak bulge in an artery. Classic features are an explosive headache, vomiting, neck stiffness, light sensitivity and sometimes collapse. Risk factors include smoking, high blood pressure, heavy drinking, cocaine use, family history and polycystic kidney disease. It is a medical emergency with high risk of death or disability, and early treatment of the aneurysm prevents rebleeding.

Reversible cerebral vasoconstriction syndrome (RCVS)

RCVS causes repeated thunderclap headaches over 1 to 3 weeks, often triggered by sex, exertion, straining, bathing or strong emotion. The brain's arteries narrow temporarily. It is more common in women aged 20 to 50, after childbirth, and with certain drugs (SSRIs, decongestants, triptans, cannabis, cocaine). Most people recover fully, but it can cause strokes or bleeding.

Other causes

Benign causes that can be sudden

• Primary headache associated with sexual activity: an explosive headache at orgasm. The first episode must be investigated to rule out bleeding or RCVS.
• Primary cough headache: brief sharp headache with coughing or straining, which also needs investigation the first time.
• Migraine occasionally starts abruptly, but a thunderclap onset should not be assumed to be migraine without testing.

What happens in the emergency department

1. Rapid assessment: blood pressure, level of consciousness, neurological examination, neck stiffness and eye exam.
2. CT scan of the head without contrast: detects most subarachnoid hemorrhages, especially within 6 hours of headache onset, when a modern scanner is very sensitive.
3. Lumbar puncture: if the CT is normal but suspicion remains, especially after 6 hours, spinal fluid is checked for blood breakdown products (xanthochromia), usually at least 12 hours after onset.
4. CT or MR angiography: images the arteries for aneurysms, dissection or the narrowing of RCVS.
5. MR venography: for venous thrombosis.

Pain relief and anti-nausea medicines are given while tests are done. Blood pressure is carefully controlled.

Treatment depends on the cause

• Ruptured aneurysm: endovascular coiling (through a catheter) or surgical clipping, ideally within 24 hours, in a specialist neurosurgical center. Nimodipine is given to reduce the risk of a later complication called vasospasm.
• RCVS: stopping triggering drugs and activities, calcium channel blockers in some cases, and pain relief. Avoid triptans and steroids.
• Artery dissection: antiplatelet medicine or anticoagulation to prevent stroke.
• Venous thrombosis: anticoagulation.
• Pituitary apoplexy: steroids and sometimes surgery.
• Spinal fluid leak: bed rest, fluids, caffeine and an epidural blood patch.

Reducing your risk

• Do not smoke, and keep blood pressure controlled.
• Avoid cocaine and stimulant drugs, and limit alcohol.
• If two or more close relatives have had a brain aneurysm, or you have polycystic kidney disease, ask your doctor about screening.

Frequently asked questions

What causes a sudden severe headache?

The most serious cause is bleeding around the brain (subarachnoid hemorrhage) from a ruptured aneurysm. Other causes include reversible cerebral vasoconstriction syndrome, artery tears, clots in brain veins, pituitary bleeding and very high blood pressure. Some cases have no cause found after full testing.

Should I go to the ER for a sudden headache?

Yes, if it reaches its worst within about a minute or is the worst headache of your life. Call 911 or your local emergency number, especially with vomiting, stiff neck, confusion, weakness or vision problems. Only hospital scans can rule out a brain bleed.

What does a brain bleed headache feel like?

People usually describe a sudden, explosive headache, like being struck on the head, reaching full strength within seconds. It often comes with nausea, vomiting, a stiff neck, light sensitivity, confusion or collapse. Some people have a milder warning headache days before.

What is a thunderclap headache?

A thunderclap headache is a severe headache that peaks within about a minute. It is a medical emergency because it can signal bleeding in or around the brain or other serious problems, although sometimes no cause is found after testing.

Can stress cause a sudden severe headache?

Stress commonly triggers tension headaches and migraines, which build gradually. A headache that hits maximum intensity within a minute should never be put down to stress until a brain bleed and other serious causes have been ruled out in an emergency department.