The choroidal neovascular membrane (MNVC) is defined as the growth of neovessels from the choroid to the pigmentary subepithelial space, through a defect of the Bruch’s membrane .
Summary
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- 1 Classification of the choroidal neovascular membrane
- 2 Methods to identify the types of membranes
- 3 Classification of neovascular membranes according to etiology
- 4 Treatment of choroidal neovascular membranes
- 5 Sources
Classification of the choroidal neovascular membrane
Most MNVC treatment indications are based on AFG classification. According to this, the MNVC can be classic, hidden or mixed.
- The classic membranecan be clinically determined by the presence of a grayish lesion, usually accompanied by hemorrhage , which may even have a true hemorrhagic halo on , with well defined edges. In the early periods of AFG, the border is well defined and then a progressive filling of the membrane occurs, which takes on a cartwheel-like appearance. In the late stages of AFG, the edges of the membrane are slightly lost by the filling of the dye. This is a classic membrane; however, there are facts that can obscure the edges of a classic neovascular membrane, such as blood, fluorescein blockade caused by hyperplasia of the pigment epithelium or fibrous tissue, and serous detachments of the pigment epithelium.
According to their location, classical membranes can be classified as extrafoveal, when the foveal edge of the membrane is beyond 200 microns from the center of the vascular zone; in juxtafoveal, when this edge is between 1 and 199 microns; and in subfoveal, when it is located under the fovea.
The big problem arises when the membrane cannot be defined with angiography.
- Hidden neovascular membranesare those in which a neovascular membrane is clinically suspected, because there is a large hemorrhagic or exudative component, but the AFG is unable to show a defined filtration pattern.
- There are mixed MNVCs, in which one component or another may predominate, which is why we speak of a predominantly classical membrane, in which a large part of the membrane behaves like a classical or predominantly hidden membrane, in which a large part of the membrane or the highest percentage of it is hidden.
Methods to identify the types of membranes
The fact that the hidden membranes do not achieve a good definition with the AFG has led to the development of new methods to better identify this type of membrane, such as green indocyanine angiography , which, in some cases, seems to give greater precision in the location and identification. of these injuries.
Green indocyanine is a dye that binds a high percentage to proteins and emits and absorbs light in the infrared range, between 805 and 835 nanometers. The characteristics of this dye make it penetrate better through pigmentary alterations and serohemorrhagic detachments.
Yanuzzidan’s studiossuggest that a percentage of the membranes hidden on angiography can benefit from the indocyanin study, in such a way that in 23% of these patients it is possible to demonstrate some more definite lesion with this dye, in cases where fluorescein failed in this goal; for example, in some cases in which the patient has a central serous detachment, a detachment of the pigmentary epithelium, a filtering lesion is suggested in the AFG, but it is not defined in the late times, because it is hidden by the epithelial detachment. In these cases, it is indicated to do a study with green indocyanine, with which it is possible to identify a plaque with greater filtration within this detachment of the pigment epithelium, obviously more defined than what the AFG allows.
According to the angiography with green indocyanine, the hidden MNVC can be of four types: the MNVC in plates, the hot spot, the polypoid vasculopathy, or the one without pattern. The fact that the hidden membranes do not achieve a good definition in the AFG has led to the development of new methods to better identify this type of membrane, such as green indocyanine angiography, which in some cases seems to give greater precision in locating and identification of these injuries.
Without a doubt, digital angiography linked to green indocyanine allows in some cases to obtain angios of much better resolution than fluorescein, although this is sometimes not true, as occurred in a patient whose fluorescein angiogram suspected a certain membrane. An area that could not be defined with this technique, nor with indocyanine angiography.
Classification of neovascular membranes according to etiology
- Age-related macular degeneration is a pathology that is increasing, as a large part of the population achieves a greater survival, thereby significantly increasing the risk of presenting this type of injury. The neovascular form of age-related macular degeneration is the main cause of blindnessin this type of patient.
Neovascular membranes in age-related macular degeneration are much more aggressive than in other pathologies, are complicated by large serohemorrhagic detachments and with a lot of exudation, and give the impression of growing day by day.
- High myopia, especially pathological myopia with large areas of posterior pole atrophy and with an axial length of 26 to 27 mm, can be complicated by neovascular membranes in a percentage ranging from 5 to 10% of cases. In the case of high myopia, these membranes are much less aggressive than in age-related macular degeneration. Generally, they are classic, small membranes with an evident hemorrhagic component, but rarely produce exudation or detachment of the pigment epithelium.
- The angioid striae, which are seen as dark brown lines that radiate from the papilla, represent areas of least resistance, in which there is an alteration of the collagenous and elastic part of the Bruch membrane, which allows the growth of the neovascular membranes.
- Traumatic choroidal ruptures can also be complicated by the appearance of neovascularization membranes.
- The choroiditis, caused by histoplasmosis and toxoplasmosis , among other agents, can also be the basis for the appearance of a neovascular membrane. Histoplasmosis syndrome is a major cause of visual impairment in young patients, in some areas of the United States , where Histoplasma capsulatum infection is endemic. If these patients are not treated, the visual prognosis in the cases with choroidal neovascular membrane is very poor; with treatment, the prognosis is much better.
- The idiopathic membrane, finally, corresponds to those cases in which the fundusand the patient itself do not have any type of pathology. Generally, it is also a classic type membrane, well defined, without exudation, which has a certain tendency to stabilize.
Treatment of choroidal neovascular membranes
The treatment of CNVM can vary depending on the underlying disease. Treatment may include anti-VEGF drugs , thermal laser , and photodynamic therapy (PDT). Depending on the course of your illness, you may receive one or more of the following treatments.
- Anti-VEGF Treatment: This is a common way of treating MNVC, attacking a specific chemical in the body that causes abnormal blood vessels to grow under the retina . This chemical is called vascular endothelial growth factor (VEGF). Several new pharmacological treatments (called anti-VEGF drugs) have been developed to block VEGF. VEGF blocking reduces MNVC growth, slows its escape, helps delay vision loss and in some cases improves it.
- Another form of treatment for MNVC is thermal lasertherapy . Laser treatment is usually outpatient in the doctor’s office , or in the hospital .
During this procedure, a high-energy laser beam produces a small burn when it reaches the area of the retina that is being treated. The beam destroys abnormal blood vessels, preventing further leakage, bleeding, and growth. After laser treatment, vision may appear more blurred than before, but it often stabilizes within a few weeks. A scar will form in the treated area, creating a permanent blind spot that can be seen within your field of vision. Normally, abnormal blood vessels are destroyed with a laser beam treatment. However, patients who undergo the procedure often need further treatment in three to five years.
- Photodynamic therapy(PDT): Photodynamic therapy (PDT) uses the combination of a light-activated medicine called a photo sensitizer, and a low-power or cold laser beam, which is directed at the MNVC. This procedure is outpatient and is usually performed in the ophthalmologist’s office. The photosensitive drug that is injected into a vein in your arm and travels through the body, including the abnormal blood vessels. The low-powered laser beam goes directly into the abnormal vessels, activating the drug, which attacks the unwanted abnormal blood vessels.
MNVC treatment can help stabilize your vision and prevent vision loss. However, many patients are unable to regain lost vision. When this is the case, it is important to learn how to make the most of the remaining vision.
