What is a vascular anomaly?
A vascular anomaly is simply a group of disorders involving abnormal blood vessels. It includes vascular tumors, which grow over time, and vascular malformations formed in early fetal development. The vascular system includes arteries that take blood away from the heart, veins that bring blood back to the heart, and an entirely separate lymphatic system that drains fluid from the tissues back into the veins. Then the capillaries are the smallest channels, literally a single cell wide, that connect the arterial system and the venous system. Vascular anomalies can involve any vessel type or combinations of vessels. For example, we see venous malformations, lymphatic malformations, arteriovenous malformations and capillary malformations. Vascular malformations are vessels that didn’t form the way nature intended during fetal development. Therefore, whether you presented at birth or when you were 12 or 32, it was something that happened as those vessels formed. There are other lesions that we classify more as vascular tumors, where there really is a lot more cell growth. They’re not tumors in the way that cancers are tumors, meaning that they don’t tend to spread to other places.
Cameron Trenor, MD
I use the term “anomaly” to be as general or generic as possible, meaning abnormal vasculature. The two major groups are tumors and malformations. Tumors are a vascular anomaly in which there is overgrowth of vascular tissue, usually the endothelial lining cells. In hemangiomas in infancy there are many other cells involved, particularly the pericytes and mast cells.
Malformations are errors of embryonic and fetal development. Most malformations are obvious at birth, but they can present later; many vascular malformations don’t present until childhood, adolescence, or adulthood.
[Later]
No classification is perfect; there is some overlap between tumors and malformations. For example, there are malformations in which there is some increased cell turnover that occurs during childhood or in adolescence. Infantile hemangiomas, in rare instances, are associated with malformations that are both vascular and non-vascular. The most well-known example is PHACES association, characterized by malformed blood vessels in the brain, malformed cardiac vessels, malformations in the brain that are not vascular, and all sorts of other strange anomalies in the eye. Although the hemangioma regresses, these other lesions usually don’t resolve.
John Mulliken, MD
Vascular anomalies can be divided into two [groups]: the tumors and malformations. The most common tumor would be an infantile hemangioma. Interventional treatment of that is rarely required unless there’s something like a neonatal who is in heart failure, in which case we will try and embolize. The vast majority of tumors will not be treated at all, they’ll just involute spontaneously.
On the other hand, the malformations, as opposed to tumors, have a normal cell turnover, so they have no capacity to grow like a tumor and similarly no capacity to go away; they’re not going to involute. These are formed during fetal life at the same time as the other vessels are formed, like veins and lymphatics, except these are abnormal collections of channels or are large sacs of lymph. They’re slightly different from normal veins. For example, a venous malformation, instead of having many layers of smooth muscle as you do in a vein in a tubular section, you have a single layer of smooth muscle so it effectively acts like a sac of blood. It kind of fills up with very low-flow and then empties out.
Lymphatic is fairly similar; it’s effectively very similar in appearance. We divide it into different areas but they don’t connect with the normal lymphatic or venous systems. Those are the two most common types of malformations. Rarer is an arteriovenous malformation in which there is an abnormal connection between artery and vein through small little vessels that we call a nidus, and then we try and embolize those.
Gulraiz Chaudry, MB, ChB, MRCP, FRCR