Subarachnoid Hemorrhage - The Worst Headache of Your Life
What a Thunderclap Headache Can Mean
The Headache That Changes the Room
Early in my training, I met a 45 year old man who woke up with thunder in his head. There was no storm outside. The sky was clear. But he described the pain as explosive, instant, maximal from the very first second.
As I spoke with him, I accidentally bumped the side of the bed. The slight vibration made his face tighten with pain. That detail stayed with me. Some headaches hurt. This one reacted to movement like the brain itself was irritated.
That was my first encounter with subarachnoid hemorrhage.
What Is Actually Bleeding?
The brain sits inside a rigid skull and is surrounded by thin protective layers. Between those layers is a space filled with clear fluid that cushions and protects the brain. That fluid is called cerebrospinal fluid, often shortened to CSF. Under normal conditions, it is crystal clear.
In a subarachnoid hemorrhage, blood leaks into that fluid filled space. Blood does not belong there. The skull cannot expand to accommodate extra volume. Even a small amount of bleeding increases pressure and irritates the surface of the brain. That irritation is what often produces the sudden, severe “thunderclap” headache.
Why Does This Happen?
The most common cause is rupture of a weakened area in a brain artery called an aneurysm. An aneurysm forms when part of a blood vessel wall becomes thin and bulges outward under pressure.
Think of a worn spot in a pressurized pipe. Over time, the weak section balloons. Eventually, it can tear. When that happens in the brain, blood escapes quickly into the surrounding fluid space. High blood pressure increases strain on these vessel walls, which is why uncontrolled hypertension is a major risk factor.
Not every severe headache is bleeding. But when someone says this is the worst headache of their life and it reached full intensity immediately, this diagnosis must be considered.
Why Is It So Dangerous?
First, the sudden rise in pressure inside the skull can disrupt brain function. People may lose consciousness. They may vomit. They may develop weakness, confusion, or difficulty speaking if nearby brain tissue is affected.
Second, blood itself irritates nearby blood vessels. In the days following the initial bleed, those vessels can narrow and reduce blood flow to parts of the brain. This can cause a stroke. Even if someone survives the first event, complications can develop later. Subarachnoid hemorrhage carries real risk. Some patients collapse before reaching care. Others survive but require intensive monitoring because the danger does not end after the first bleed.
How Do We Diagnose It?
The first step is usually a CT scan of the head. Fresh blood appears bright on CT imaging. When performed within the first six hours after headache onset, a high quality CT scan is very sensitive for detecting bleeding. In that early window, a normal scan significantly lowers the likelihood of subarachnoid hemorrhage.
However, timing matters. If the CT is performed later, or if clinical suspicion remains high despite a normal scan, a spinal tap may be necessary. In that test, we examine the clear fluid around the brain for red blood cells or signs that blood has broken down. If bleeding is confirmed, imaging of the brain’s blood vessels is performed to look for an aneurysm.
How Is It Treated?
Blood pressure must be managed carefully. Too high increases the risk of further bleeding. Too low reduces blood flow to the brain. This balance requires close monitoring, often in an intensive care unit.
If an aneurysm is identified, specialists may seal it from the inside using a minimally invasive procedure. Through a catheter placed in an artery, tiny coils are delivered into the weakened pouch to block blood flow into it. In other cases, surgery is performed to place a small clip across the base of the aneurysm. The goal is simple: prevent re bleeding.
Why This Diagnosis Matters
Most headaches are benign. Stress. Migraine. Dehydration. But occasionally, the story changes everything. Sudden onset. Maximal at the start. A patient who says this is different from anything they have felt before. Because bleeding inside a closed skull leaves no room for error.
THE BOTTOM LINE
• Subarachnoid hemorrhage is bleeding into the fluid space around the brain, most often caused by rupture of a weakened artery
• It typically presents as a sudden severe headache that reaches maximum intensity immediately
• Early CT imaging, and sometimes spinal tap, are critical for diagnosis and preventing fatal complications
Written by a Board-Certified Emergency Medicine Physician