||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX; Professor of Ophthalmology, Weill Cornell Medicine; Ashley Huang, Baylor College of Medicine Class of 2023
||So, today we're going to talk about vascular malformations as they apply to the eye. And as the word implies, a MAL-formation is poorly-formed. And when we're talking about vascular malformations, it can be the really small vessel, capillary; it can be the vein, venous; it can be the artery; and it can be endothelial lined channels, which is cavernous. So we can have a capillary malformation, a venous malformation, an arterial venous malformation, called an AVM, and a cavernous malformation. Each of these have different and distinctive ways that they look, and their risk of hemorrhage is different. So a capillary malformation is what we call a telangiectasia. So it's a very small, fine vessel that kind of looks like a little squiggly line like this. And that is unlikely to cause a big hemorrhage because it's so small and so low pressure but it can bleed. And then we have the venous malformation. And in the brain, we call those developmental venous anomalies (DVAs). So the development of this venous anomaly looks like a hemorrhoid, like a dilated vein and then a little branch through it. And that's also unlikely to bleed because it's a low pressure system. Then we got the one that's the high pressure system, that's the arterial venous malformation. There's the arterial feeder, and then there's the nidus. No capillary bed. And then draining veins. So an arterial venous malformation is an arterial feeder nidus, no capillary bed. And because there's no capillary bed to draw down the pressure, the venous side is high as well. This one has a high risk of hemorrhaging. And then you've got cavernous malformation. The cavernous malformation is actually just endothelial lined channels, a collection of caverns, hence the name. And these caverns have blood cells inside them. And because the cavernous malformations can bleed at various times, we have different ages of the bleeding. And on an MRI scan, we can see the different ages because the age of the blood can be determined by the aging process of the hemoglobin. So normally in the normal state we have oxyhemoglobin. And then we go to deoxyhemoglobin. And we go to methemoglobin. And that methemoglobin can be intracellular or extracellular. And finally, the chronic form hemosiderin. And on an MRI scan we can see that as a variable intensity and the methemoglobin tends to be bright on T1. It's one of the few things that's actually bright on T1 that methemoglobin. We can also see it as a susceptibility artifact. And the grading echo sequences on MRI and hemosiderin is dark on both T1 and T2. So the bright signal on T1 or the dark signal on T1 and T2 tells us these are older-aged blood based on the aging of the hemoglobin as it passes from oxyhemoglobin to deoxyhemoglobin to intracellular and extracellular methemoglobin, and finally to hemosiderin. So in a patient who has a cavernous malformation, we might see high signal on T1 with the surrounding rim of low signal representing the methemoglobin and the hemosiderin in the same patient. And so these vascular malformations are malformations. They're not really tumors, and it's really important that we differentiate these from the blood vessel tumors which call hemangiomas. And so even though in the literature there are some books that say cavernous hemangioma, what we really mean is a cavernous malformation. And I prefer to limit the use of the word hemangioma to the blood vessel tumors: capillary hemangioma and hemangioblastoma. And so these vascular malformations you need to know about but also because they can appear both in your eye and in your head. So when we have telangiectasias, we are worried about telangiectasias in other parts of your body. That's Osler-Weber-Rendu and those can be associated with nosebleeds and GI bleeds. Or ataxia telangiectasias: thetelangiectasias appear in the conjunctiva, but could also appear - uh - in your head and that is called Louis-Bar. And the patients who have arterial venous malformations, that's Wyburn-Mason. You can have an AVM in your eye, you can have an AVM in your brain. And if you have a cavernous malformation in your eye, you can have a cavernous malformation in your brain. That actually has no name, no eponym attached to it, even though it probably is also a phacomatosis. In addition, we have the blood vessel tumors, the hemangiomas. You could have the port-wine stain on the face, and the ipsilateral leptomeningeal hem-uh-vascular malformation in Sturge-Weber syndrome. And you could have a coronal hemangioma, making it a tomato-catsup fundus, either a diffuse or localized form of hemangioma, and a hemangioblastoma in the retina and in your cerebellum or elsewhere in your central nervous system, and that disease is called the Von-Hippel-Lindau syndrome. So you need to know what the vascular malformations are, differentiate them from tumor, understand the anatomy of each of these, their bleeding risks, and how they can appear both in the eye and in your brain.