A cerebral vasospasm is the term used to describe when a brain artery or smaller brain blood vessels narrow. A blood vessel’s central lumen becomes narrow in response to the vessel wall contraction. This constriction prohibits blood flow.
Although a cerebral vasospasm usually occurs as a result of a brain aneurysm that has ruptured, it can also be caused by the hemorrhaging of a vessel that is caused by a blood vessel abnormality. It is believed that any increase in pressure around an outer portion of a blood vessel, whether blood or fluid, can trigger a vasospasm. This belief coincides with vasospasms that occur following the rupture of an aneurysm. With blood vessel abnormalities, such as an arteriovenus malformation (AVM), the narrowing of vessels is a response to the pressure caused by the abnormality.
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While most cerebral vasospasm cases occur from excessive bleeding from a rupture or complications from an abnormality, there are instances when a vasospasm can occur as a result of a hemorrhage from severe head and brain trauma. In these cases the subarachnoid cavity is filled with blood, called a subarachnoid hemorrhage (SAH), but in smaller amounts than a ruptured aneurysm. A traumatic brain injury causes the SAH, which then causes the vasospasm.
Doctors believe that a cerebral vasospasm occurs in the arteries and not in smaller vessels because of the wall structures. Compared to smaller veins, arterioles, or capillaries, the arteries have a thicker layer of smooth muscle, which makes the wall thicker. This thicker wall means more constriction.
Cerebral vasospasm occurs mainly in the Circle of Willis, which is a vascular ring at the base of the brain. The main branches of this ring are more prone to a vasospasm, but the smaller arteries can also develop problems. Smaller arteries around the surface of the brain are also vulnerable.
The three types of classifications for a cerebral vasospasm are subangiographic, clinical, and angiographic. A vasospasm is classified into one of these three groups based mainly on its size. Patients can suffer from all the signs of a vasospasm, but it cannot always be detected.
When the narrowing is not pronounced enough or the affected vessel is difficult to see, a cerebral angiography will not be successful in locating the spasm. The patient may or may not have symptoms. In this case, the spasm is classified as a subangiographic cerebral vasospasm.
If the cerebral vasospasm can be detected using an angiography, with or without symptoms, it is classified as an angiographic vasospasm. In most instances patients show some symptoms, but the amount of symptoms experienced will vary depending on the location and severity of the spasm. Clinical vasospasms are the type that presents with all of the tell-tale symptoms, and regardless of what an angiography shows, a doctor can diagnose the spasm.