Would a CT scan show a brain bleed?

Yes, a CT scan can detect brain bleeds. CT scans use X-rays and computers to produce detailed images of the inside of the body. They are one of the best imaging tests for viewing the brain and can quickly detect bleeding and other abnormalities.

What is a CT scan?

A CT or CAT scan (computed tomography scan) is a specialized X-ray test that produces cross-sectional images of the body using X-rays and a computer. The images provide more detail than a regular X-ray.

During a CT scan, the person lies on a table that slides into a tunnel-like machine. X-rays rotate around the body and are picked up by detectors on the other side. The detectors send signals to a computer that complies multiple X-ray images into cross-sectional views of the body.

How does a CT scan detect brain bleeds?

CT scans are very sensitive at picking up acute bleeding in the brain. Blood appears bright white on CT scan images, so even small amounts are easily visible.

This is because blood contains iron, which is very dense compared to other tissues in the body. The dense blood shows up as brighter white on the grayscale CT images.

Fresh blood clots also have a characteristic appearance that radiologists can recognize.

Some key signs of acute bleeding on a CT scan include:

  • Bright white areas representing blood pools or clots
  • Dark spots indicating bleeding inside brain tissue
  • Enlarged blood vessels or pooling of contrast dye indicating bleeding
  • Distorted anatomy structures pushed aside by accumulating blood
  • Skull fractures or other signs of head trauma

Radiologists look for these hallmark signs when diagnosing a brain bleed. Even tiny bleeds as small as a few millimeters can be detected on CT scans.

What types of brain bleeds can be seen on CT?

CT scans can detect several different types of intracranial hemorrhage (bleeding within the skull), including:

  • Subarachnoid hemorrhage: Bleeding into the space between the brain and the surrounding membrane (subarachnoid space), usually from a ruptured aneurysm.
  • Subdural hematoma: Bleeding between the dura mater and the arachnoid membranes, caused by head trauma.
  • Epidural hematoma: Bleeding between the inside of the skull and the outermost membrane layer (dura mater), also due to trauma.
  • Intracerebral hemorrhage: Bleeding directly into the brain tissue, can have various causes including high blood pressure, aneurysms, head injury, blood thinning medications.
  • Intraventricular hemorrhage: Bleeding into the fluid-filled ventricles within the brain.

These various types of hemorrhages have different appearances on CT scans and different symptoms. But CT imaging can accurately detect all of them.

What are the advantages of CT for detecting brain bleeds?

There are several reasons why CT scans are ideal for detecting acute intracranial hemorrhage:

  • Speed: CT scans are very fast. Modern scanners can complete a head CT in just a few minutes.
  • Availability: CT scanners are widely available in hospitals and emergency departments.
  • Accuracy: CT reliably detects small amounts of new bleeding in the brain.
  • High resolution: CT provides clear, detailed images that pinpoint the location of bleeding.
  • Blood flow: CT scans can also assess ruptured blood vessels and impaired blood flow.
  • Other findings: CT shows other important findings like skull fractures, mass effects, hydrocephalus.

This makes CT ideal as an initial emergency imaging test when a brain bleed is suspected clinically. It can rapidly confirm bleeding and help determine the next steps in treatment.

Are there any limitations of CT for detecting brain bleeds?

CT scans have some limitations including:

  • Cannot detect microscopic bleeding or subtle chronic blood products.
  • Less sensitive for small subarachnoid hemorrhages.
  • Uses ionizing radiation, although the amount is low.
  • Does not show as much detail as MRI for distinguishing different tissues.
  • May require injected contrast dye which has side effects.
  • Cannot be performed on some patients with metal implants or devices.
  • Relatively expensive test.

However, for diagnosing acute cerebral hemorrhage, CT is still the first line imaging test in emergency situations. The benefits outweigh limitations in most cases of suspected active bleeding.

When should a CT scan be done for suspected brain bleed?

Emergency medical providers will order a stat head CT scan if symptoms suggest an acute intracranial hemorrhage, including:

  • Sudden severe headache
  • Loss of consciousness
  • Mental status changes
  • Seizures
  • Nausea and vomiting
  • Weakness or vision changes
  • Slurred speech
  • Confusion
  • Head trauma

Many of these are red flag symptoms that require rapid imaging to look for bleeding as the cause. Even if the symptoms later resolve, a bleed may have occurred, so a CT scan is still warranted.

Stable patients with subtler neurological changes may get an MRI or lumbar puncture first. But CT remains the go-to initial test for suspected brain bleeds requiring prompt diagnosis.

How quickly can a CT scan detect a new bleed?

CT scans can detect acute bleeding immediately after it occurs. However, very small amounts of bleeding may take several hours to become visible on CT as it takes time for a sizable pool of blood to accumulate.

For major hemorrhagic strokes or traumatic bleeds, CT scans will show evidence within minutes to hours after the event. Repeat CT scans over the next 1-3 days will also confirm if bleeding is continuing or resolving.

In some cases, neurological symptoms arise days after a minor hemorrhage. A delayed CT scan may then detect subtle signs of old bleeding. So CT evidence of hemorrhage can emerge rapidly or gradually depending on the circumstances.

Can old bleeds be seen on CT scans?

As blood breaks down in the brain, it undergoes characteristic changes in appearance on CT.

  • Hyperacute blood (within 1 day) – Bright white, high density
  • Acute blood (1-3 days) – Slightly lower density white
  • Early subacute blood (3 days to 1 week) – More heterogeneous, mixed density
  • Late subacute blood (1-2 weeks) – Darker gray clot with surrounding edema
  • Chronic blood (after 2 weeks) – Dark gray or black, with contraction

So even old bleeds that occurred weeks or months prior can still be visible on CT scans due to these residual blood products. However, CT is not as sensitive as MRI for definitively dating old hemorrhages.

Can minor bleeds be seen on CT scan?

Yes, CT scans can detect even minor amounts of intracranial bleeding down to a few millimeters in size. The high inherent contrast of blood compared to other brain tissues allows small hemorrhages to be visible.

However, tiny petechial hemorrhages smaller than 1-2 mm may not always show up on CT scans. CTs are excellent at detecting volumes of acute bleeding over 5-10 ml, which are likely to cause clinical symptoms. But scattered microhemorrhages can be difficult to appreciate without MRI.

Can a CT scan miss a brain bleed?

Modern CT scanners very rarely miss acute brain bleeds that are clinically significant. However, no test is perfect, and some potential reasons a brain bleed could be missed on initial CT include:

  • Very small subarachnoid hemorrhage in narrow sulci or fissures
  • Chronic small bleeds with minimal residual blood products
  • Bleeding later obscured by edema, mass effect, or ischemia
  • Inadequate image quality or patient motion artifact
  • Incorrect radiological technique or suboptimal IV contrast timing
  • Rare vascular malformation or aneurysm not recognized
  • Interpretation error by the radiologist

For these reasons, a normal head CT cannot completely exclude an underlying intracranial hemorrhage as the cause of neurological symptoms. Repeat imaging or other tests may be needed if clinical suspicion remains high. But such occurrences are uncommon.

What if CT scan is normal but symptoms suggest a bleed?

If the initial head CT scan is negative but signs and symptoms suggest an intracranial hemorrhage is likely, further assessment is warranted.

Next steps may include:

  • Obtaining a lumbar puncture test if subarachnoid hemorrhage is suspected
  • Repeating the CT scan in 12-24 hours
  • Performing a CT angiogram to assess blood vessels
  • Ordering an MRI scan for more sensitivity
  • Monitoring in the hospital with serial neurological exams
  • Evaluating other causes like mass lesions, stroke, or seizures

With advances in CT technology and technique, most bleeding events can be detected on the first scan. But if clinical doubt remains, additional imaging and workup should proceed to rule out an underlying hemorrhagic process not seen on initial CT.

Can CT contrast dye help detect brain bleeds?

Yes, intravenous contrast enhancement is commonly used and can boost the accuracy of head CT scans for detecting acute bleeding.

The iodine-based contrast material brightly highlights blood vessels on CT. This allows better visualization of arteries, veins, and any abnormal leakage of blood from ruptured vessels.

In particular, CT angiography (CTA) with contrast can precisely map blood vessel anatomy and reveal underlying vascular abnormalities causing hemorrhage like aneurysms, AVMs, and sinus thrombosis.

However, head CT without contrast is usually adequate to identify sites of active bleeding from straightforward trauma, hypertensive hemorrhage, hematomas, and similar etiologies.

So contrast enhancement is not essential but can provide valuable additional information in some cases of suspected brain bleed. It carries a small risk of allergic reaction or kidney problems.

What is the typical process for getting a head CT scan?

The process for having a head CT scan usually includes:

  • A doctor orders CT imaging based on symptoms
  • Little preparation is required, unlike MRI scans
  • Patients remove metal objects and may change into a gown
  • An IV is started, usually in the arm, hand or wrist
  • The patient lies still on the CT table which slides into the scanner tunnel
  • Patients must stay very still during the quick scan, usually just seconds
  • A radiologist later interprets the CT images on a computer
  • The diagnostic report is sent back to the ordering doctor
  • Total time is 30-60 minutes, with the actual scan taking under 15 seconds

So CT scanning is quick and convenient compared to other imaging tests. Results are available rapidly, often within an hour in emergency cases.

Can a CT scan tell if a brain bleed is old or new?

Radiologists can usually determine whether a brain hemorrhage is acute or chronic based on certain CT characteristics:

  • New bleeds are bright white, uneven, lobulated, mixed density, surrounded by edema.
  • Old bleeds are darker, uniform, with sharp borders, retracted clots, calcium deposits, gliosis, and encephalomalacia.

CT is excellent at detecting fresh bleeding but has limitations determining the precise age of older hemorrhages. After about 2 weeks, it becomes difficult to distinguish subacute from chronic blood.

MRI with special sequences can more accurately date blood breakdown products in the brain over time. But CT provides a quick, reliable way to differentiate new bleeding from old.


In summary, CT scans can reliably detect both new and old bleeding in the brain. They are the fastest, most widely available initial imaging test for diagnosing an intracranial hemorrhage.

CT technology allows even tiny hemorrhages to be visualized. Typical bleeding patterns help radiologists distinguish traumatic, hypertensive, aneurysmal, and other causes.

While CT may miss subtle or chronic bleeding, it excels at identifying acute hemorrhage and guiding rapid treatment in emergencies. When brain bleed is suspected, a head CT scan is standard and critical for determining next steps.

Leave a Comment