The SDH medical abbreviation stands for subdural hematoma, a pool of blood that collects between the brain's tough outer covering, the dura, and the brain itself. It is usually caused by a head injury that tears small veins on the surface of the brain.
SDH shows up in emergency notes, CT head reports, neurosurgery consults and trauma records. Older adults and people taking blood thinners are at higher risk, and in them even a minor fall can be enough. It is often discussed alongside TBI, traumatic brain injury. This page explains the anatomy behind the name, acute versus chronic SDH, and the other kinds of bleeding inside the skull.
At a glance
What the SDH medical abbreviation means
Three protective membranes surround the brain. The outermost and toughest is the dura mater. Beneath it lies the arachnoid, and closest to the brain is the pia. Small bridging veins cross the space under the dura. A sudden jolt can tear them, and blood slowly gathers in that space. That collection is a subdural hematoma.
As the brain shrinks somewhat with age, these veins are stretched further, which is one reason older adults are more prone to SDH. Blood thinners and heavy alcohol use also raise the risk.
Acute, subacute and chronic SDH
| Type | Rough timing after injury | Typical features |
|---|---|---|
| Acute | Within a few days | Often after a significant blow; symptoms can appear quickly |
| Subacute | Days to a few weeks | A middle stage as the blood begins to change |
| Chronic | Weeks or longer | Common in older adults; may follow a minor fall that was forgotten |
Chronic SDH can cause slowly growing headaches, confusion, weakness or unsteadiness that is easy to mistake for other problems in older people. Exact timing labels vary a little between sources and radiologists.
Reading a CT head report with SDH
Radiology line: "Acute L convexity SDH measuring 8 mm, 3 mm rightward midline shift." This says fresh blood lies over the outer curve of the left side of the brain, up to 8 millimeters thick, and it is pushing the middle structures of the brain 3 millimeters toward the right.
Midline shift is an important detail because it shows pressure on the brain. On CT, an SDH typically looks crescent shaped as it spreads along the brain surface. A note might also mention ICP, intracranial pressure, if pressure inside the skull is a concern.
SDH compared with other brain bleeds
- Epidural hematoma (EDH): blood above the dura, usually from an artery; often lens shaped on CT.
- SAH: subarachnoid hemorrhage, bleeding under the arachnoid layer, often from an aneurysm or trauma.
- ICH: intracerebral hemorrhage, bleeding inside the brain tissue itself.
- IVH: intraventricular hemorrhage, blood in the fluid spaces of the brain.
The diagnosis abbreviations hub groups these and other conditions.
Treatment terms and questions to ask
Small SDHs may be watched with repeat scans. Larger ones, or those causing symptoms, may be drained. A burr hole is a small opening in the skull used to drain chronic SDH, while a craniotomy is a larger opening for thicker, acute clots. Notes may also mention reversing or holding blood thinners.
- How large is the bleed, and is it changing?
- Will I need repeat imaging?
- What symptoms should prompt urgent care?
Subdural bleeding is summarized here in general terms only. Your neurosurgery or emergency team can explain what a specific scan result means for you.
Frequently asked questions
What does SDH stand for on a CT report?
SDH stands for subdural hematoma, a collection of blood between the dura, the brain's tough outer covering, and the brain surface.
What is the difference between SDH and SAH?
An SDH lies beneath the dura, usually from torn veins after an injury. SAH is bleeding in the space under the arachnoid layer, often from a burst aneurysm or trauma.
Can a subdural hematoma happen after a minor fall?
Yes, especially in older adults or people on blood thinners. A chronic subdural hematoma may appear weeks after a fall that seemed minor at the time.
What is a chronic SDH?
It is a subdural hematoma that has developed slowly over weeks or longer. It can cause gradual headaches, confusion or weakness and is more common in older people.