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Abnormalities of the head and neck arteries (Cerebrovascular Abnormalities)
What are cerebrovascular abnormalities?
A cerebrovascular abnormality is an abnormal blood vessel of the brain. In the case of PHACE syndrome, patients can have abnormalities of the arteries that carry blood to the brain either in the head (cerebral) or neck (cervical). The arteries in the chest, neck and brain are the most frequent arteries found to be abnormal in PHACE syndrome. These blood vessels can have abnormal shapes, sizes or paths through the neck and head.
What are the arteries of the chest, neck and brain?
Blood is carried to the brain through blood vessels called arteries. Arteries are defined as blood vessels that carry blood away from the heart to deliver oxygenated blood to the tissues of the body. Blood is initially pumped from the heart into the aorta, the body's biggest artery. It then travels up to the brain through smaller branching arteries. The first branch off of the aortic arch is the innominate artery (also called the brachiocephalic artery), which provides blood to the right side of the head and neck. The innominate artery immediately branches into the right subclavian artery and right common carotid artery. The second branch off of the aorta is the left common carotid artery. The third branch off of the aorta is the left subclavian artery.
|Figure 4: Major arteries of the head, neck, and brain|
Both the right and left common carotid arteries divide into the external and internal carotid arteries at the carotid bifurcation. The internal carotid arteries carry blood directly to the front and middle parts of the brain while the external carotid artery carries blood to the face and scalp.
Both of the subclavian arteries carry blood mainly to the arms, but they also carry blood to the brain through branching of the vertebral arteries. The vertebral arteries arise from the subclavian arteries and carry blood up toward the brain along the spinal column. These arteries fuse together and form the basilar artery which supplies blood to the back of the brain.
The blood travelling from the back of the head through the basilar artery and the blood traveling from the front of the head through the internal carotid arteries meet at the circle of Willis. The circle of Willis is a circular group of arteries that provides a connection for blood flowing from the back to the front of the body.
Why is the Circle of Willis important?
The circle of Willis is very important because it helps to make sure oxygen and nutrient-rich blood reaches all areas of the brain. In a way, it is considered the backup system for blood supply to the brain and serves the same function as a highway bypass, allowing for an alternate route if there is a traffic jam in the normal route. For example, if there is a blockage in the left internal carotid artery and blood is not able to reach the front of the left side of the brain, blood can move from the right internal carotid artery through the anterior communicating artery to the left side of the brain. In this example, if the circle of Willis did not exist, there would be no way for blood to reach the back of the brain. The brain is the body's most vital organ, and it must have a constant supply of blood to work properly. If the blood supply to the brain is interrupted, a stroke can result. When nerve cells in the brain are damaged or die, the functions they control, such as movement, speech and learning may be affected. The effects of a stroke on a child's ability to function depend on the area of the brain which is damaged; the symptoms may be temporary or permanent (see Neurologic Abnormalities section).
|Figure 5: Detail of the Circle of Willis|
What cerebrovascular abnormalities are seen in children with PHACE syndrome?
The blood vessels of the head and neck in children with PHACE syndrome can be abnormal. The five main types of abnormalities are:
This describes an artery that has abnormal looping, kinking, elongation or dilation.
The width of the arteries is smaller than normal.
This means that there is an absence of a normal artery because it did not form, or it is not seen on an MRI/MRA because blockage prevents the flow of contrast through the vessel.
- Abnormal course or origin
This means that the artery does not deliver blood to where it normally does or that it branches off (begins) from an abnormal point
- Persistent fetal arteries
This is when blood vessels that usually disappear after birth are still present.
What arteries are most commonly affected?
The internal carotid artery is the most frequently involved abnormal artery. According to a recent study, anomalies of the internal carotid artery are present in about 75 percent of PHACE syndrome patients who have cerebrovascular abnormalities. The abnormal artery is most often located on the same side as the facial hemangioma.
What persistent fetal arteries are seen in PHACE syndrome?
The trigeminal artery is the most common persistent fetal artery seen in approximately 12-19 percent of PHACE syndrome patients. Persistent hypoglossal (3 percent) and stapedial (1.5 percent) arteries can also be observed. These fetal arteries are normally open and functional for a short period of time during fetal development. The trigeminal artery and hypoglossal arteries connect the blood vessels of the front and back of the head and neck. The stapedial artery connects the internal carotid and external carotid arteries. Children with persistent fetal arteries may be at an increased risk for an aneurysm (balloon-like growth) or dilation (widening) at the point where the persistent fetal vessel joins a normal artery.
How common are abnormal arteries of the head and neck seen in children with PHACE syndrome?
Besides the hemangioma on the skin, abnormal blood vessels of the head and neck are the most common abnormality seen in children with PHACE syndrome. It has been estimated that greater than 80 percent of children with PHACE syndrome have at least one abnormal artery in their neck or head, and many have several abnormal arteries in this region.
Currently, the exact reason why PHACE syndrome patients have abnormal arteries of the head and neck is not known, but researchers have some ideas. Physicians believe that there are defects in the formation of the internal carotid arteries during fetal development that causes decreased blood flow. Due to the lack of blood flow, the vessels that would normally branch off the internal carotid artery and supply the brain do not form correctly. It is believed that this is why some fetal remain – to allow flow to parts of the brain that otherwise wouldn't receive adequate blood flow.
How is a cerebrovascular abnormality diagnosed?
A cerebrovascular abnormality cannot be determined by physical exam, so special radiologic imaging is needed. An MRI/MRA of the head and neck, a computed tomography angiogram or an angiogram may be used to diagnose the underlying blood vessel abnormalities. Depending on what the imaging studies show, repeat imaging may be needed at a later date.
What are some of the complications involved with having abnormal arteries?
Some PHACE syndrome patients with abnormal arteries of the head and neck may have an increased risk of stroke, seizures, and motor or language developmental delays as compared to children with normally formed arteries. A stroke is the loss of brain function due to disturbance in blood supply to the brain. The risk of stroke in children with PHACE syndrome with abnormal arteries is unknown but it is believed to be very rare. Of the total number of PHACE syndrome patients reported in the literature (a little more than 400), there are only approximately 20-25 reported to suffer from an acute ischemic stroke. All of these patients had abnormalities of the cervical (neck) and cerebral (brain) arteries, and many had other medical conditions. They were most commonly found to have narrowing of the internal carotid artery or middle cerebral artery. Physicians and researchers are still working to develop a systematic way of identifying which PHACE syndrome patients are at an increased risk of stroke so they can be closely followed and managed.
How can parents tell if their child is having a stroke or seizure?
Symptoms of a stroke or seizure could include abnormal eye movements, tremor, decreased body tone (limpness), head bobbing, limb or body weakness, inability to move the limbs or body, headache or absence of breathing (see Neurologic Abnormalities section).
Are there any treatments to prevent strokes or seizures?
Currently there are no guidelines to treat PHACE syndrome patients who have had strokes or seizures, or who are believed to be at an increased risk for either. Children who have had a stroke or seizure, or who are believed to be at an increased risk for these may be treated by their physician with aspirin.
What research is being done regarding cerebrovascular abnormalities in PHACE syndrome patients?
A multidisciplinary team of physicians have done research to evaluate the MRA/MRI of PHACE syndrome patients with cerebrovascular abnormalities to determine if these abnormalities stay the same or change over time. With the information obtained in this study, physicians hope to be able to establish guidelines for when patients need MRA/MRI and to establish the best treatment to limit stroke risk.