Brain Boo-Boos: Cerebrovascular Accidents (Stroke)

MCA Stroke CT Scan

Stroke - ADC Map

Stroke - Diffusion Weighted
A cerebrovascular accident, commonly known as a stroke, occurs when blood flow stops reaching brain tissue. If the entire brain is involved it is referred to as a "global" stroke; if a specific region of brain is involved it is referred to as a "focal" or "territorial" stroke. There are three broad causes of territorial strokes: thrombotic, embolic, and hemorrhagic.

A thrombotic stroke occurs when a blood clot forms in a blood vessel that supplies brain tissue. This is similar to what happens in cardiac infarction (ie: heart attacks). Thrombi are most commonly caused by atherosclerotic disease of the cerebral blood vessels. Thrombi usually form at areas of turbulent blood flow and at locations where vessels form branch points.

Embolic strokes are similar because they are technically blood clots. However, an embolus is a fragment of a clot (thrombus) that formed in another part of the body. Those fragments break free from the original clot and travel to blood vessels in the brain. They get lodged at some point and prevent blood from flowing resulting in a stroke if treatment is not obtained quickly.

Strokes can also be caused by bleeding into brain tissue. These type of strokes are called “hemorrhagic stroke”. Bleeding can occur in people with long standing untreated high blood pressure, or in those that have underlying structural disorders of the blood vessels in the brain (ie: aneurysms or arteriovenous malformations).


Speedy diagnoses of stroke is extremely important because brain tissue dies quickly if it doesn’t receive adequate oxygen.

The first test that is done in cases of suspected stroke is a CT scan of the head. The purpose of the CT scan is not necessarily to "see" the stroke, but rather to rule out some other cause (ie: tumor, subdural hematoma, etc) for the symptoms. If bleeding is present on the CT scan the treatment algorithm becomes much different. If no bleeding is seen on CT then the second scan is usually an MRI.

An MRI takes longer than a CT scan, but it gives a much more detailed picture of the brain. In addition, it can pick up ischemia (ie: cell death related to decreased blood flow) much earlier than CT.

The best sequences to detect a stroke on an MRI are the diffusion weighted images and apparent diffusion coefficient maps. Stroked brain tissue will appear “bright” on diffusion weighted imaging and “dark” on the apparent diffusion coefficient map (see images to the left).

In addition, the carotid arteries are scanned using ultrasound in order to detect potential narrowing from atherosclerotic disease. Atherosclerotic carotid arteries are a potential source of emboli.

Sometimes a procedure known as transcranial doppler, which also uses ultrasound technology, is used to detect blood flow in the individual blood vessels of the brain. This can sometimes help determine the specific location of the thrombus/embolus.

Cerebral angiograms are much more invasive tests, but give a detailed view of which vessels are blocked. Cerebral angiograms can also be used to treat some strokes by directly removing clot from the affected blood vessel.

Most patients should undergo a thorough work up for atherosclerotic disease including a fasting lipid panel and hemoglobin A1C levels (a marker of diabetes).

If the heart is a suspected source of emboli than transthoracic echocardiography (ie: an ultrasound of the heart) is often done as well.

Signs and Symptoms

Cerebrovascular accidents present with a wide variety of signs and symptoms. It is entirely dependent on the blood vessel, and therefore, region of the brain involved. For example, strokes in the left middle cerebral artery will often cause significant language impairments if left untreated. Middle cerebral artery strokes usually cause contralateral paresis as well (usually the face and arm are more affected than the leg). Strokes in the frontal lobes caused by blockage of the anterior cerebral arteries can cause personality changes, as well as paresis/paralysis of the contralateral lower extremity.

Suffice it to say that there are a variety of possible clinical presentations in patients suffering from stroke. These presentations generally correlate with our understanding of brain anatomy and function.


Prompt treatment of stroke is critical for preserving viable brain tissue. If a stroke is due to a blood clot (ie: thrombus or embolus) the treatment is with a drug known as tissue plasminogen activator (tPA). tPA is a medication that helps break up the clot.

It can be a dangerous medication because it can cause serious bleeding, but if given early enough, and in the right patient, it can completely prevent brain tissue death. There are numerous contraindications to giving tPA so caution must be used. The traditional teaching is that is should be given within three hours of symptom onset (this is the FDA approved indication); however, up to 4.5 hours from symptom onset has become common in clinical practice (but this is not FDA approved).

Endovascular therapies that mechanically remove the clot are becoming more common, especially for large vessel disease. However, this type of treatment requires specialized interventional neuro-radiologists and is not available in all medical centers. Endovascular therapy with a clot retrieving device is usually indicated up to 6 hours post symptom onset for large vessel occlusions. More distal (ie: further out) occlusions are not candidates for this type of procedure yet.

If a patient survives their first stroke, they are often started on medications to decrease their risk of having a second stroke. One of the most common medications used to prevent a second stroke is aspirin.

However, other medications like ticlopidine and clopidogrel (Plavix®) are also frequently used. All three of these medications prevent platelets (ie: one of the bodies natural ways of forming blood clots) from clumping together. In addition, aspirin is often mixed with another medication called dipyridamole (dipyridamole + aspirin = Aggrenox® in the United States). Patients who have suffered a minor stroke or have high risk transient ischemic attacks should be started on aspirin and clopidogrel and then transitioned to aspirin alone at 21 days.

If atherosclerosis is believed to be the cause of the stroke patients are often started on a statin. This helps slow the process of atherosclerosis and can help prevent another stroke from occurring.

If an embolus was the cause of the stroke patients are often started on an anticoagulant. The most common one used is warfarin (although there are many others). Warfarin is also used to treat a common cause of embolic stroke, an abnormal heart rhythm known as atrial fibrillation.


Strokes can be caused by thrombi or emboli which are blood clot that block blood flor, or from hemorrhage into brain tissue. Diagnosis is made by CT and MRI scans. Additional studies including carotid ultrasound, cerebral angiography, echocardiography, fasting lipid profiles, and tests for diabetes are also frequently performed.

Treatment depends on the etiology. Tissue plasminogen activator (tPA) is given if thrombi or emboli are the cause, and symptoms began less than 3 hours prior to presentation (4.5 hours is becoming the standard of care). Mechanical endovascular removal of the clot is also possible in some medical centers with specialized equipment.

Prevention of secondary strokes involve the use of anti-platelet (ie: aspirin, clopidogrel), anti-coagulant (ie: warfarin), and anti-atherosclerotic medications depending on the etiology of the previous stroke.

Related Articles

References and Resources

When Brain Veins Go Bad: Cerebral Sinus Thrombosis

In order to understand cerebral sinus thrombosis, we need a quick overview of blood vessel anatomy and the normal direction of blood flow in the body. In the most general terms, blood flows from the heart to large arteries (ie: aorta) then smaller arteries (branches off the aorta) then even smaller vessels called capillaries. It is at this point where the different body tissues extract nutrients and oxygen from the blood. The blood then drains into progressively larger veins until it empties back into the heart where it is re-oxygenated.

The largest veins of the brain are referred to as cerebral venous sinuses. They include the superior sagittal sinus, inferior sagittal sinus, a pair of transverse sinuses, a pair of sigmoid sinuses, straight sinus, cavernous sinus, a pair of superior petrosal sinuses, a pair of inferior petrosal sinuses, and the occipital sinus. The role of these sinuses is to collect all the “used” blood from the brain and deliver it back to the heart.

Like other veins in the body, the cerebral sinuses can form blood clots in them (the technical term for a blood clot is actually a "thrombosis", hence the name “sinus thrombosis”). When this happens a back up of blood in the brain occurs leading to increased pressure and sometimes hemorrhage within the brain tissue itself.

The exact cause of a dural venous thrombosis is not always clear. However, there are numerous risk factors associated with their development. They include inherited defects in proteins responsible for blood clot formation. These defects are collectively known as “thrombophilias”, which in Latin means “thrombus loving”. People with these inherited issues are more prone to forming blood clots.

In addition, patients with a kidney condition known as nephrotic syndrome are at increased risk. In this condition patients urinate out proteins responsible for keeping the blood clotting system at bay. The resulting imbalance can cause blood clots to form where they normally would not.

Infections such as mastoiditis and meningitis can cause inflammation of the sinuses, which can result in blood clot formation. Trauma to the head can also cause clot formation. In addition, that beautiful parasitic infection known as pregnancy (a joke of course!) also increases the risk of developing blood clots. Many commonly used birth control pills, especially those containing estrogen, can also increase a person’s risk.

Signs and Symptoms

Depending on the severity of the clot, everything from a mild headache (the most common presenting symptom) to death is possible. Patients with severe headaches may also have associated nausea and vomiting secondary to elevated intracranial pressures. Decreased mental status is also sometimes observed.

It is also important to remember that not all sinuses are created equal. For example, thrombosis in the superior sagittal sinus can present with leg weakness secondary to edema (ie: swelling) of the adjacent motor cortex.

If a clot forms in the cavernous sinus it may cause dysfunction of the third, fourth, fifth, and/or sixth cranial nerves. In addition, when blood pools in the brain behind the clot it can result in a type of stroke known as venous infarction.


With todays modern imaging studies, MRI, and more specifically, MR venography has become a crucial diagnostic aid.

An example of an MR venogram is shown in the picture below. Other commonly used tests include traditional angiograms, in which radio-opaque dye is injected directly into the sinuses through catheters inserted in the groin. Finally, CT scans are also commonly obtained, especially to evaluate for possible co-existent hemorrhage into the brain.

MRV of Cerebral Sinus Thrombosis


Treatment is usually with a blood thinning medication known as heparin. It is delivered through an IV and helps prevent further clot formation. If a venous stroke is present the use of blood thinning medications must be weighed against the possibility of causing bleeding into the stroked brain tissue. Aggressive hydration with normal saline is also often advocated.

Treating other underlying co-problems such as seizures and increased intracranial pressure is also an important part of managing patients with cerebral sinus thrombosis. Patients with substantial increases in intracranial pressure may require removal of the skull (craniectomy).


Cerebral sinus thrombosis is a abnormal blood clot in one of the large venous draining systems of the brain. They are uncommon and can present with everything from a mild headache to coma and death. Diagnosis is made most commonly with MRI. Treatment is based on preventing further clot formation with heparin and aggressive hydration.

References and Resources

  • Xu H, Chen K, Lin D, et al. Cerebral venous sinus thrombosis in adult nephrotic syndrome. Clin Nephrol. 2010 Aug;74(2):144-9. Review.
  • Dlamini N, Billinghurst L, Kirkham FJ. Cerebral venous sinus (sinovenous) thrombosis in children. Neurosurg Clin N Am. 2010 Jul;21(3):511-27.
  • Ju YE, Schwedt TJ. Abrupt-onset severe headaches. Semin Neurol. 2010 Apr;30(2):192-200. Epub 2010 Mar 29.
  • Kamal AK. Thrombolytic therapy in cerebral venous sinus thrombosis. J Pak Med Assoc. 2006 Nov;56(11):538-40.
  • Greenberg MS. Handbook of Neurosurgery. Sixth Edition. New York: Thieme, 2006.