Vascular malformations are abnormal changes in blood vessels that are typically present at birth, though they may not become noticeable until later in childhood or even adulthood. These abnormalities can appear anywhere in the body and range from harmless birthmark-like marks to serious conditions requiring medical attention.

What Are Vascular Malformations?

Vascular malformations are abnormalities involving blood vessels or lymphatic vessels that develop when these vessels form incorrectly during a baby’s development before birth. Unlike tumors that grow rapidly and often disappear on their own, vascular malformations grow slowly throughout a person’s life and do not go away without treatment.^[1]

These abnormalities can affect different types of vessels in your body. The blood vessels that might be involved include arteries (vessels that carry oxygen-rich blood from your heart to your body), veins (vessels that carry blood back to your heart), and capillaries (tiny vessels that connect arteries and veins). Vascular malformations can also affect lymphatic channels, which are part of the immune system and carry a clear fluid called lymph.^[1]

The way these vessels connect and function becomes disrupted in vascular malformations. Instead of forming normal, organized networks, the affected vessels may become tangled, enlarged, or connected in abnormal ways. This disrupted structure can cause various problems depending on where the malformation is located and which vessels are involved.^[5]

Vascular malformations can develop anywhere in the body, from the top of the head to the toes. They may appear on the skin’s surface as colored marks that look like birthmarks, or they may develop deep inside the body near important organs, the brain, or the spinal cord. Some malformations are visible right away, while others remain hidden for years before being discovered.^[1]

Epidemiology

Vascular malformations are considered rare conditions in the general population. Some types are found in less than 1 percent of people worldwide. The overall occurrence of all types of vascular malformations together is estimated at around 1.5 percent of the population.^[2][11]

Among the different types, venous malformations are the most common, representing approximately 65 percent of all vascular malformations. These develop in veins and can occur anywhere in the body.^[2][11]

Arteriovenous malformations, which involve both arteries and veins, occur with equal frequency in men and women. Between 40 and 60 percent of these malformations are apparent at birth, and an additional 30 percent become noticeable during childhood.^[11]

Most vascular malformations are present from birth, although they may not be immediately visible. In a study of consecutively treated patients over several years, females outnumbered males, with 86 females and 37 males among 123 cases. The average age when treatment began varied, but the conditions affected people across different life stages.^[11]

The rarity of these conditions means that many people visit multiple doctors before receiving an accurate diagnosis. This delay can lead to confusion and anxiety for patients and their families as they search for medical professionals who understand these complex abnormalities.^[2]

Causes

Vascular malformations result from developmental errors that occur during embryogenesis, which is the period when a baby is developing in the womb. These errors happen in the very early stages of blood vessel and lymphatic vessel formation, typically before a baby is born.^[5]

The underlying cause involves abnormal signaling processes in the body that normally control how vascular cells grow, mature, and function. When these signals go wrong, cells that should form normal blood vessels instead create abnormal structures. The result is the persistence of vascular cells that have not differentiated or organized correctly into functioning vessels.^[5]

In some cases, genetic mutations play a role in causing vascular malformations. These genetic changes can affect the instructions that cells use to build blood vessels, leading to abnormalities in their structure and function. However, most vascular malformations occur sporadically, meaning they happen by chance rather than being inherited from parents, similar to how birthmarks appear randomly.^[6]

While vascular malformations are congenital (present at birth), there is a small subset that can develop during adulthood after trauma or another significant incident. However, this is rare, and the vast majority of malformations originate before birth.^[1]

The specific type of malformation that develops depends on which stage of vessel development was affected and what kind of vessels were involved. If capillaries fail to develop properly, a capillary malformation results. If veins or arteries are affected, different types of malformations emerge. Sometimes multiple types of vessels are involved, leading to combined or mixed malformations.^[1]

Risk Factors

Most vascular malformations occur sporadically, meaning they are not associated with specific risk factors that can be modified or avoided. They happen by chance during fetal development, and in most cases, there is no family history or identifiable cause.^[6]

However, certain genetic conditions and syndromes are associated with a higher likelihood of developing vascular malformations. Children with Down syndrome, Turner syndrome, overgrowth syndromes (genetic disorders that cause unusual increases in body size), and Noonan syndrome have a greater chance of having lymphatic malformations compared to the general population.^[6]

Some vascular malformations that are present from birth may not cause problems until they are triggered by certain life events or changes in the body. Adolescence is one such trigger period when hormonal changes can cause a previously unnoticed malformation to grow or become symptomatic. Pregnancy is another common trigger, as the significant hormonal and blood volume changes during this time can make malformations more prominent or problematic.^[2]

Physical trauma, major surgery, or injury can also activate or worsen vascular malformations. The stress on the body’s circulatory system from these events may cause a malformation that was stable and asymptomatic to suddenly enlarge or begin causing symptoms.^[2]

Age itself can be a factor in how malformations behave. As people grow older, malformations tend to grow proportionally with the body. Some malformations that were barely noticeable in childhood can become more extensive and problematic over time, particularly during periods of rapid growth.^[5]

Symptoms

The symptoms of vascular malformations vary greatly depending on where they are located in the body, how large they are, and which type of blood vessels are involved. Some people with vascular malformations have no symptoms at all, while others experience significant problems that affect their daily lives.^[1]

Many vascular malformations first appear as visible changes on the skin. These may look like birthmarks, red or purple patches, or areas of discoloration. Some appear as soft lumps under the skin that may be smooth to the touch, while others feel firm or solid. The appearance can range from a small spot to large areas covering significant portions of the body.^[1][6]

Pain is a common symptom for many people with vascular malformations. The pain may be constant or may come and go. It can range from mild discomfort to severe pain that interferes with daily activities. The affected area may also feel tender or painful to touch.^[1]

Swelling is another frequent symptom. The area around the malformation may become swollen, and in cases involving the arms or legs, the entire limb can become enlarged. This swelling may worsen after physical activity or at certain times of the day.^[1][6]

When vascular malformations occur in the head, face, or neck, they can cause specific problems related to their location. If a malformation affects the mouth or tongue area, it can make eating, swallowing, or speaking difficult. Malformations near the eyes can interfere with vision. Those affecting the throat or airways can cause breathing difficulties.^[6]

Vascular malformations in the brain or spinal cord can cause more serious symptoms. These may include headaches, seizures, neurological deficits (problems with movement, sensation, or coordination), or bleeding within the brain, which is a life-threatening emergency.^[1][9]

Some malformations affect the function of nearby body parts. They may impair vision if they are near the eyes, or limit movement if they involve joints or muscles. When they grow large enough, they can put pressure on surrounding tissues, organs, nerves, or bones, causing additional symptoms.^[1]

Lymphatic malformations can form fluid-filled cysts that may grow gradually or suddenly. These cysts can sometimes become infected, leading to redness, warmth, increased pain, and drainage. Some lymphatic malformations cause chronic small bumps, blisters, or bloody crusts on the skin surface that may rupture and ooze clear fluid or blood.^[6]

Venous malformations can form blood clots within the abnormal vessels. These clots may cause sudden pain and swelling, and in rare cases, pieces of clots can travel to other parts of the body, including the lungs, which can be dangerous.^[6]

Prevention

Because vascular malformations are congenital abnormalities that develop during fetal growth, there are no known ways to prevent them from occurring. The developmental errors that lead to these malformations happen before birth, and currently, no lifestyle changes, dietary modifications, or other interventions during pregnancy have been shown to reduce the risk.^[5]

Most vascular malformations occur sporadically by chance, without any identifiable cause that could be avoided. They are not caused by anything the mother did or did not do during pregnancy. Parents should understand that these conditions are not the result of maternal behavior, diet, or environmental exposures.^[6]

In the small number of cases where vascular malformations are associated with genetic syndromes, genetic counseling may be helpful for families planning to have children. A genetic counselor can discuss the risks of passing on certain genetic conditions and explain the available options for family planning.^[6]

While vascular malformations themselves cannot be prevented, it is possible to take steps to prevent them from becoming symptomatic or worsening. For people who know they have a vascular malformation, avoiding triggers that can make it worse is important. This includes being cautious with activities that could cause trauma to the affected area.^[2]

Early detection is valuable even though prevention is not possible. Some vascular malformations can be identified during pregnancy through prenatal ultrasound or fetal MRI. This early identification allows parents and doctors to prepare for any necessary treatments or interventions after birth.^[6]

Regular medical follow-up is important for people with known vascular malformations. Monitoring the malformation over time helps doctors detect any changes or growth early, allowing for timely intervention before serious complications develop. This is especially important during periods of rapid growth, such as adolescence, or during pregnancy.^[2]

Pathophysiology

The underlying problem in vascular malformations is that blood vessels or lymphatic vessels do not form properly during development. All vascular malformations share a common feature: they are lined by a single layer of endothelial cells, which are the cells that normally line the inside of all blood vessels. However, the structure and organization of the vessels themselves are abnormal.^[5]

Unlike vascular tumors, which involve abnormal cell growth and multiplication, vascular malformations are not caused by excessive cell division. Instead, they result from errors in how the vascular structures are built and organized. The cells themselves are not multiplying abnormally; they are simply arranged in the wrong pattern or form vessels of the wrong size and shape.^[5]

Vascular malformations are classified based on the type of blood flow through them. Low-flow malformations involve vessels where blood moves slowly or not at all. These include capillary malformations, venous malformations, and lymphatic malformations. High-flow malformations involve arteries where blood moves rapidly under high pressure. These include arteriovenous malformations and arteriovenous fistulas.^[8]

In venous malformations, the veins are enlarged and form abnormal, dilated channels. Blood pools in these channels and moves very slowly, which can lead to blood clots forming inside the malformation. The slow-moving blood and clots can cause pain and swelling. Because these vessels are abnormal, they may not have the normal supporting structures around them, making them fragile and prone to problems.^[2]

Arteriovenous malformations involve a direct abnormal connection between arteries and veins. Normally, arteries carry blood to capillaries, which then connect to veins. In an AVM, the arteries connect directly to veins through a tangled cluster of abnormal vessels called a nidus. This means blood flows directly from the high-pressure arterial system into the veins without going through capillaries first. This can “steal” blood from surrounding normal tissues, depriving them of oxygen and nutrients. The high-pressure blood flow can also weaken vessel walls, making them prone to rupture and bleeding.^[1][10]

Lymphatic malformations occur when lymphatic vessels fail to connect properly to the normal lymphatic drainage system. Instead, lymph fluid accumulates and forms cysts or masses. These can be single large cysts (macrocystic) or multiple small cysts (microcystic), or a combination of both. The trapped fluid can sometimes contain blood from nearby vessels, causing swelling and discoloration.^[6]

Capillary malformations, which include port-wine stains, involve abnormally widened capillaries in the skin. These capillaries are wider than normal and may be more numerous. While they are limited to the superficial layers of the skin initially, over time they can thicken and become more prominent. Some may develop nodules or become bumpy and disfiguring.^[8]

Cavernous malformations in the brain consist of tightly packed abnormal capillaries that form cavern-like spaces. Blood moves very slowly through these caverns, and the vessel walls are fragile. This makes them prone to small hemorrhages, which can cause symptoms ranging from headaches to seizures.^[1]

The growth of vascular malformations throughout life is related to normal body growth and hormonal changes. During periods of rapid growth, such as childhood and adolescence, malformations tend to grow proportionally. Hormonal changes during puberty and pregnancy can trigger rapid expansion. Trauma or inflammation can also stimulate growth of the malformation.^[2]