The SAH medical abbreviation means subarachnoid hemorrhage, which is bleeding into the space between the brain and the thin tissue layers that cover it. That space normally holds clear cerebrospinal fluid, and blood there irritates the brain and raises intracranial pressure.
SAH is a medical emergency. Readers find it in emergency notes, head CT reports, neurosurgery and neuro intensive care charts. The two main causes are head injury and a burst bulge in a brain artery called an aneurysm. This page explains the word parts, how SAH reads on a scan report, how it compares with bleeds such as SDH, and the shorthand clinicians use around it.
At a glance
Stands for
Subarachnoid hemorrhageWord roots
Sub, beneath; arachnoid, the spider web like middle covering of the brain; hemorrhage, bleedingMain causes
Head trauma; ruptured brain aneurysmFirst test
CT head without contrastWhere you see it
ED notes, radiology reports, neurosurgery and ICU chartsDo not confuse with
SDH (subdural) and IVH (bleeding into the ventricles)
What the SAH medical abbreviation describes
Three thin coverings, the meninges, surround the brain. From outside in they are the dura, the arachnoid and the pia. The subarachnoid space lies under the arachnoid and is filled with cerebrospinal fluid that cushions the brain. A subarachnoid hemorrhage means blood has leaked into that fluid filled space.
When the bleed comes from a ruptured aneurysm, people often describe a sudden, explosive headache, sometimes called a thunderclap headache or the worst headache of their life. Nausea, vomiting, a stiff neck, light sensitivity, confusion or loss of consciousness can follow. Anyone with a sudden severe headache like this needs emergency care right away.
Traumatic versus aneurysmal SAH
| Type | Cause | How notes often word it |
|---|---|---|
| Traumatic SAH | Head injury from a fall, crash or blow | tSAH, small traumatic SAH |
| Aneurysmal SAH | A weak, ballooned artery wall that bursts | aSAH, aneurysmal SAH |
| Other spontaneous SAH | Less common causes, such as an AVM | Nonaneurysmal SAH |
Trauma is the most common cause overall, and small traumatic bleeds are often watched with repeat scans. Aneurysmal SAH is less common but usually more serious, because the aneurysm can bleed again until it is treated.
Reading SAH on a CT report
Radiology impression: "CT head: diffuse SAH in basal cisterns, CTA to r/o aneurysm." Here the noncontrast head scan shows blood spread through the fluid spaces at the base of the brain. The radiologist suggests a CTA, a scan of the blood vessels, to rule out an aneurysm as the source.
Basal cisterns are pockets of spinal fluid at the base of the brain. R/o means rule out. If a CT is normal but suspicion stays high, a lumbar puncture may be done to look for signs of blood in the spinal fluid.
How SAH differs from other brain bleeds
Brain bleeds are named by where the blood collects. An epidural hematoma lies outside the dura, against the skull. A subdural hematoma, SDH, lies under the dura. A subarachnoid hemorrhage is deeper again, in the fluid space next to the brain surface. Bleeding inside the brain tissue itself is called intracerebral or intraparenchymal hemorrhage, and blood in the fluid chambers deep in the brain is intraventricular hemorrhage, written IVH.
These locations look different on CT and are treated differently, so the abbreviation tells the care team a great deal at a glance. A hemorrhagic stroke is also charted under the broad heading CVA in some records.
Terms often charted after an SAH
- Vasospasm: narrowing of brain arteries days after an aneurysmal bleed, watched closely in the ICU.
- Hydrocephalus: a build up of spinal fluid, sometimes drained with an EVD.
- ICP: intracranial pressure, which can climb when blood or fluid builds up.
- Coiling or clipping: ways to seal off an aneurysm from the inside with a catheter or from the outside in surgery.
Grading scales are also recorded to describe how severe the bleed looked at the start. For other brain and nerve conditions, see the diagnosis abbreviations hub.
Brain bleeds need care from a specialist team, and every case is different. Ask the neurosurgery or neurology team how an SAH finding applies to your family member.
Frequently asked questions
What does SAH mean on a CT scan?
SAH on a CT report means subarachnoid hemorrhage, blood in the fluid space around the brain. The report usually adds where the blood is and how much is seen.
Is SAH a type of stroke?
A subarachnoid hemorrhage from a ruptured aneurysm is generally counted as a type of hemorrhagic stroke. Traumatic SAH from a head injury is usually grouped with traumatic brain injury instead.
What is the difference between SAH and SDH?
Both are bleeds around the brain, but in different layers. SDH, subdural hematoma, sits under the tough outer dura, while SAH sits deeper in the fluid filled subarachnoid space.
What does tSAH mean?
The small t stands for traumatic, so tSAH means a subarachnoid hemorrhage caused by a head injury. It is often seen with other injuries listed under TBI.