Subdural Hematoma: When to Cut

Subdural Hematoma: When to Cut

Subdural hematoma is a common neurosurgical problem. A subdural usually occurs in patients with significant brain atrophy, such as the elderly or alcoholic. Even minor trauma can injure the bridging veins between the brain and the dura. Bleeding into the subdural space can occur rapidly, causing death in a matter of hours, or gradually over a period of weeks. The surgical management depends on whether the hemorrhage is acute or chronic.

Acute Subdural Hematoma

An acute subdural may result from trauma or in a patient on antiplatelet or anticoagulant drugs. Symptoms often include headache, hemiparesis or alteration of consciousness like agitation, lethargy, or coma. If the acute subdural is small, it can be managed non-surgically. Antiplatelet drugs are stopped, and coagulation is corrected. Careful clinical observation is imperative. The subdural may expand as it becomes chronic, as the osmotic effect of the blood products draws free CSF into the subdural space. All this to say, if a small, acute subdural isn’t surgical today, it may be in two weeks!

Here a moderate sized, acute subdural is seen. You will notice a hyperdense (white) mass over the cortical surface of the brain (arrow), with effacement of the gyral pattern adjacent to the subdural, along with asymmetry of the lateral ventricles and midline shift.

Acute subdural hematoma

This patient was taken to surgery for a craniotomy. In the craniotomy, a large section of the skull was removed. This is called “turning a flap.” It allows the evacuation of the blood clot. At surgery, the clot was so tenacious it could be picked up with forceps. This, by the way, is the reason that an acute subdural cannot be drained with a bur hole. The blood is congealed. It cannot be drained with a bur hole any more than a cup of Jello can be eaten with a straw: it is solid. Air is introduced into the head at the time of surgery. It appears jet black on CT (arrow).

Acute subdural hematoma post op

Chronic Subdural Hematoma

On CT, a chronic subdural is hypodense (dark). It represents old blood in a liquid state. How old is old? It takes about two weeks for an acute subdural to liquefy, and the CT appearance will evolve from hyperdense to hypodense as the hemorrhage becomes chronic. Symptoms include headache on the same side as the subdural. Hemiparesis may be mild or well compensated as weakness occurs gradually. Many patients experience hemiparesis as gait imbalance, or veering to one side. As the patient worsens, frank lethargy or coma may ensue.

Here is a chronic, subacute subdural hematoma. You see a hypodensity over the cerebral convexity anteriorly (double arrow), with a hyperdense component posteriorly (arrow). There is effacement of the gyral pattern, ventricular asymmetry and midline shift.

Subacute chronic subdural hematomaChronic subacute subdural hematoma with labels

This patient was taken to the operating room for bur-hole evacuation of the subdural. The liquefied blood was removed with a simple bur hole. Going back to the Jello analogy: If you leave Jello at room temperature, it turns to liquid; in this case you CAN drink it with a straw. Or drain a chronic subdural with a bur hole!

Here you can see postoperative air in the head (jet black, see arrow), with a mix of residual chronic and subacute blood, with improved mass effect. A drain is present (double arrow).

Chronic subdural hematoma post opChronic subdural hematoma post op with labels

To summarize, an acute subdural is a life threatening emergency, often requiring craniotomy within hours. The chronic subdural can be life threatening as well, but over a period of weeks, often treated with simple bur hole drainage.

When to get a CT Head

When to get a head CT?

How do you know when to order a head CT? A patient presents with headache or confusion: should you get a scan now? Here is a mnemonic that can help you know when to get a head CT on a patient with neurological symptoms.

SCAN – NOW. Get a CT Head if . . .

Seizure: new onset seizure

Confusion, or any change in mental status

Acute onset: a “new and different” headache

Nuchal rigidity: the stiff neck of meningitis or subarachnoid hemorrhage

Neuro deficit: any focal neuro change, like unequal pupils or pronator drift

Optic papilledema: a sign of increased intracranial pressure

Worrisome history: like malignancy, anticoagulants, or prior bleed or known lesion

For the patient with complaint of headache, always ask, “Is this the same old headache that’s bothered you so long … or IS THIS NEW AND DIFFERENT?” The “new and different headache” needs a CT.

For the headache patient, always perform a funduscopic exam, looking for optic papilledema, a sign of increased intracranial pressure. Every headache workup needs a funduscopic exam!

Nuchal rigidity is a classic sign of meningitis and is caused by the irritation of the meninges caused by bacteria and white blood cells in the CSF. This irritation is heightened by flexion of the neck, as the meninges are stretched. In a subarachnoid hemorrhage, red blood cells in the CSF cause a similar irritation of the meninges, aggravated by neck flexion. This nuchal rigidity is also associated with Kernig’s sign and Brudzinski’s sign. Any patient with headache and nuchal rigidy requires an immediate CT of the head. (And in the presence of acute illness or fever suggesting meningitis, immediate administration of antibiotics, even before the diagnostic workup is completed.)

Head CT: a Systematic Reading

How to read a Head CT

BoneAirWaterBrain – and sometimes Contrast

CT Head is the most common cranial imaging study you’ll see. It’s as common in neurosurgery as a chest xray is in internal medicine. And just like the chest xray, you need to approach it systematically. A systematic reading of the images will save you from the common error of looking only at the most obvious abnormality to the neglect of other significant findings. Like seeing an obvious meningioma on the parietal convexity, and missing a smaller meningioma at the optic nerve.

All that to say, you’ve got to approach the head CT in a systematic fashion to avoid costly mistakes.

So here’s an approach: BoneAirWaterBrain – and sometimes Contrast. Today we start with bone windows.

CT head: Bone window


Start with bone windows and look for fracture, especially around the orbits and zygomatic arch. Don’t mistake normal skull suture lines for fractures, but remember that some fractures occur at the suture. Look for widening of the suture or displacement of the fracture.


Keep it on bone windows, but this time look at the air spaces in the head, specifically where air should be: the sinuses and mastoid air cells, looking for air-fluid levels which might suggest a CSF leak. Now look for air where it should not be: at the meninges, especially at vertex, along the interhemispheric fissure, and along the frontal convexity. Air appears jet-black on CT, whether bone or brain windows.


Now with the window set for brain, the CSF spaces should be examined for size and symmetry. If the lateral and third ventricles are abnormally large, consider normal pressure hydrocephalus.

CT head: brain window

If the temporal horns of the lateral ventricles are enlarged, think about acute obstructive hydrocephalus. If you see asymmetry of the lateral ventricles, or the fourth ventricle is not midline, you have evidence of mass effect.


Examine the brain tissue. Sometimes you can differentiate gray and white matter along the cerebral convexity. Look for the hyperdensity of an acute intraparenchymal hemorrhage, or calcifications of an oligodendroglioma. A hypodensity suggests ischemic stroke, but an acute CVA will present with a NORMAL CT. The CT changes do not appear for 24-28 hours after the stroke. In the image below: “There is a hyperdensity deep within the right cerebral hemisphere, with mild edema and mass effect, without midline shift.”


Use contrast for tumor or infection (abscess). But in most cases, if tumor or abscess if suspected, you’ll get an MRI without and with contrast anyway, so skip the CT contrast. Contrast is most useful in a CT-Angiograpy for evaluating possible aneurysm or AVM. For example, if CT for evaluation of a headache reveals a subarachnoid hemorrhage, immediately add contrast for a CT-Angiogram to search for an aneurysm.

CT head: non-contrastCT head: with contrast

The CT on the left is without contrast. The right image reveals peripheral enhancement of this deep right lesion. “There is a peripherally enhancing mass deep within the right cerebral hemisphere, with marked effacement of the right lateral ventricle and 8 mm right to left midline shift.”

In approaching a head CT, read it systematically: BoneAirWaterBrain – and sometimes Contrast.