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Disease Information : CVM

Congenital Vascular Malformation : What is it?

What is CVM?

Birthmarks, Vascular Malformations, and Anomalies

Vascular anomalies occur in barely 1% of all births. Yet, because of their rarity, their proper diagnosis and treatment is difficult, as most physicians do not see these problems often enough to become knowledgeable about their management.

What are they

“Vascular anomalies” is an all-inclusive term for vascular malformations, vascular tumors, and other congenital vascular defects. The more commonly used term, Congenital Vascular Malformation (CVM), implies abnormally formed blood vessels that one is born with. However, in spite of its redundancy, CVM is a popular term and it will be used here.

Birthmarks occur on the surface of the body and are relatively easy to deal with. Other vascular malformations can develop from any type of blood vessel and develop in any part of the body, although the majority involves the extremities. They represent defects or development problems that occurred during embryonic growth. Depending on the state of development at the time this occurs, the result can involve arteries, veins, lymph vessels, or combinations of these.


The difference between a CVM and a vascular tumor or hemangioma (the medical term), both of which are commonly called “birthmarks” is very important to the child. Although they may initially appear the same, “all birthmarks are not the same.” Most birthmarks represent a superficial vascular malformation, consisting of abnormal collections of small blood vessels near the skin. Typically, this CVM type of “birthmark” does not go away nor does it enlarge, growing only at the same rate as the child. It thus maintains the same size and appearance indefinitely, is not a health threat, and requires no immediate treatment. Some of them, because of their location, particularly around the face and neck or on some other exposed body part, are unsightly and cosmetically disturbing. Fortunately, the characteristic reddish color coincides with the range of certain lasers that can be used for their destruction. Another approach has been to cover them up by tattooing them a skin color.

The other type of birthmark may appear the same at first, but is actually a true vascular tumor or hemangioma. In contrast, this type undergoes rapid growth in the months after its discovery, but then almost miraculously it “involutes” or gets progressively smaller. The majority disappears completely in a few years, leaving behind a patch of shrunken elastic skin. This regression normally is competed between two and eight years of age, but not all of them completely disappear. During their growth phase, these “juvenile hemangiomas” can be alarming, particularly if they grow in a critical location, such as those on the face impinging on the eye, nose, or mouth, in which case they may require treatment. However, most juvenile hemangiomas do not require treatment. Rather the best advice is to do nothing but wait it out, giving it a chance to go away by itself.

Both of these types of birthmarks, or the remnants of them, can be greatly improved in appearance by plastic surgery, but this is only occasionally needed and can usually be done after the child grows up.

Arterial-Venous CVMs

During early developmental stages, large connecting channels or shunts between future arteries and veins exist, and a defect or arrest occurring at this stage may allow these artery-to-vein connections, or a cluster of them, to persist. Such connections are called arteriovenous fistulas (AVFs), of if there is a cluster of them they are called arteriovenous malformations (AVMs). These are potentially the most serous type of CVMs because in shunting blood from arteries to veins, they bypass the small vessels that make up the normal circulation beyond that point. This not only robs or steals blood that would otherwise pass through to more distant tissues and nourish them, but doesn’t allow for a gradual pressure drop from the high arterials pressure to the low pressure on the venous side. Thus, these AVFs represent a high flow short-circuit, and depending on their size and location they may respectively force the heart to work harder. They may also cause poor circulation in the limb beyond the point of the ACVF. In time, these AVFs tend to get bigger and have greater effect on the circulation. For example, and AVF or AVM in an extremity can “steal" (reduce) blood flow to a foot or hand ad much as a blocked artery would. Fortunately, AVFs located in the legs and arms are more common than elsewhere in the body and thus easier to deal with. Those involving pelvic vessels, or vessels to vital organs or the brain can be extremely difficult to trek without injuring the organs or tissues they lie in. Clearly, although AVFs make up only one third of all CVMs, they attract the most attention because of the more serious nature of the problems they create, and are the CVMs most likely to need interventional treatment.

Venous CVMs

CVMs composed entirely of veins, which are numerically the most common, comprising almost half of the total, are of two basic types. The more primitive ones appear as thin-walled lakes in which venous blood collects and when they develop in groups or clusters, they may form a mass consisting of a collection of grape-like clusters of these venous lakes. This type usually does not affect the venous circulation which returns blood to the heart, but these masses of venous malformation can be unsightly, cumbersome, or be the site of blood clots (which fortunately, are not the kind that travel to the heart or lungs). They are more annoying than being a serious threat, but nevertheless, may be worth treating if the mass is large and causes local problems, for example, interfering with walking.

The other type of venous defect involves the large deep or central veins and often interferes with their function. Segments of major veins may be absent or narrowed. Or segments may be greatly widened and expanded (dilated), called a venous aneurysm. Depending on how severely they affect venous return or contribute to deep vein thrombosis (DVT) determines treatment. Most of the venous malformations involve only short venous segments and do not require treatment.

Arterial CVMs

Arterial defects or malformations are the least common type of CVM, being responsible for only 1-2 percent of the total. The most common arterial defect involves a segment that did not develop. The result is that a normal arterial segment is missing and instead blood flows through a normally undeveloped side channel or collateral artery, which persists rather than withers. Although this allows bypassing the blockages, the enlarged bypassing segment often becomes more vulnerable to compression and injury, developing into an aneurysm or suddenly clotting off. The most common example of this is the so-called persistent sciatic artery.

Congenital Vascular Malformation section was last modified: November 07, 2011 - 05:27 pm

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