Retinal Arterial Macroaneurysms
NEAL H. ATEBARA
Table Of Contents
FLUORESCEIN ANGIOGRAPHIC APPEARANCE
|Retinal arterial macroaneurysms, first systematically studied by Robertson in 1973, are fusiform or saccular dilations of the retinal arteries, usually associated with systemic hypertension and atherosclerotic vascular disease. They may follow a benign clinical course, but if they leak fluid or hemorrhage, they can result in significant loss of central visual acuity. Management options depend on the nature of the exudative or hemorrhagic complications of the macroaneurysm. This chapter reviews the clinical presentation, pathophysiology, and management of retinal arteriolar macroaneurysms.|
|The typical patient who presents with a retinal arterial macroaneurysm is older than 60 year of age with a history of systemic hypertension and arteriosclerotic vascular disease. Women are affected three times more often than men.1,2 There may be a sudden loss of central or peripheral vision due to hemorrhage, a gradual blur in central visual acuity due to cystoid macular edema, or the macroaneurysm may be found ophthalmoscopically on a routine examination if there is no exudation or hemorrhage that encroaches upon the fovea. The incidence of retinal arterial macroaneurysms increases with age.|
|The hallmark for diagnosis of the retinal arterial macroaneurysm is visualization
of the macroaneurysm itself (Fig. 1). Because of their relatively large size, macroaneurysms are not
usually confused with the microaneurysms of diabetic retinopathy or branch
retinal vein occlusion. Microaneurysms typically have a diameter
of only 50 to 75 microns and arise from the deeper retinal capillaries; macroaneurysms
on the other hand range in size from 100 to more than 500 microns
in diameter and arise from the larger retinal arterioles.|
Retinal arterial macroaneurysms usually arise within the first three orders of bifurcation from the optic disc (Fig. 2), often at a point of arteriovenus crossing. Sometimes they occur directly on the optic nerve head3 or on a cilioretinal artery.4 About 20% of affected eyes have multiple aneurysms, and about 10% demonstrate macroaneurysms in both eyes.
Retinal arterial macroaneurysms often produce retinal edema, circinate hard exudates, and hemorrhage (Fig. 3) into multiple layers of the retina: beneath the retinal pigment epithelium, beneath the retina, within the retina, beneath the internal limiting membrane, between the retina and the posterior hyaloid, and within the vitreous cavity. When the macroaneurysm is obscured by overlying blood, its diagnosis can be challenging.
|FLUORESCEIN ANGIOGRAPHIC APPEARANCE|
|Because of rapid blood flow through retinal arterial macroaneurysms, they
typically fill quickly in the early phase of the fluorescein angiogram. In
the mid- and late-phases of the angiogram, the macroaneurysm
tends to leak to varying degrees, depending on its perfusion
and endothelial integrity (Fig. 3C). If there is subretinal fluid surrounding the aneurysm, there may
be pooling of dye into the subretinal space. In some cases, a characteristic
Z-shaped kink may be identified at the site of the aneurysm.|
Perfusion abnormalities caused by the macroaneurysm cause changes in the surrounding retinal vasculature as well, and this is best visualized on fluorescein angiography (Fig. 3B). Ischemia from stagnation of blood flow results in capillary telangiectasis, microaneurysm formation, and capillary nonperfusion.
Some or all of these angiographic features may be obscured by blood or lipid exudation from the aneurysm. If blood collects in front of the retinal vessels (vitreous hemorrhage, preretinal hemorrhage, subinternal limiting membrane hemorrhage, or intraretinal hemorrhage), then blockage of hyperfluorescence may be partial or complete. Subretinal blood blocks hyperfluorescence from the choroid but not the retinal circulation, resulting in dramatically distinct retinal vessels against a dark background (Fig. 3B,C). Lipid exudation and retinal edema may cause partial blockage of hyperfluorescence.
|Chronic systemic hypertension is often seen in patients with retinal arterial
macroaneurysms, and it is believed this condition has an important
role in its pathogenesis. It is hypothesized that chronic vascular
wall damage secondary to systemic hypertension and arteriosclerosis leads
to focal dilation of the vascular wall, and this leads to macroaneurysm
formation.5 There is no adventitia where arteries and veins cross, and this is a point
at particular risk for aneurysm formation.|
There is also evidence that retinal arterial macroaneurysms may be caused by focal damage to the blood vessel wall from conditions such as embolus,6 toxoplasmosis infection,7 or branch retinal vein occlusion.8
|The diagnosis of retinal arterial macroaneurysm is based on ophthalmoscopic
identification of the macroaneurysm. The macroaneurysm is easily
distinguished from microaneurysms—such as those seen in diabetes
mellitus, branch retinal vein occlusion, sickle cell disease, and radiation
retinopathy—which are smaller in size.|
Retinal capillary hemangiomas (von Hippel's angiomatosis) are rare tumors seen in the peripheral retina or on the optic disc. When fully developed, they are usually much larger than macroaneurysms, often larger than 5 mm in diameter. They often result in significant subretinal fluid exudation and cystoid macular edema. They bleed less frequently than macroaneurysms. Peripheral retinal capillary hemangiomas usually arise near the ora serrata, whereas macroaneurysms usually arise within three orders of bifurcation from the optic disc. Retinal capillary hemangiomas of the optic disc grow to sizes much larger than macroaneurysms and almost always result in poor visual acuities.
Hemorrhage can obscure funduscopic visualization and make the differential diagnosis of a macroaneurysm more challenging.
|Most retinal arterial macroaneurysms do not require any treatment. If the
macroaneurysm produces no exudation or hemorrhage, in most cases, they
may be simply observed (Fig. 4). Some macroaneurysms pulsate due to the arterial pulse pressure, and
this feature may represent an increased risk of bleeding in the near
If exudation or hemorrhage threaten or affect central vision, several management options exist depending on the clinical situation; laser photocoagulation, Nd-YAG laser photodisruption, pneumatic displacement of hemorrhage, and vitrectomy with surgical evacuation of blood have all been employed in the treatment of retinal arterial macroaneurysms.
Laser photocoagulation (Fig. 3D) directed to the area surrounding the macroaneurysm or to the macroaneurysm itself is indicated when subretinal blood begins to threaten central vision or when exudation threatens or affects central vision.9–11 Photocoagulation causes the macroaneurysm to thrombose and sclerose. This decreases the risk of another hemorrhage and usually reduces the amount of exudation. The main risk of this procedure is that it may itself cause thrombosis of the adjacent branch retinal artery, possibly resulting in a central or peripheral scotoma depending on its location.12 If the macroaneurysm is sufficiently thin walled, photocoagulation may even induce bleeding in rare cases.
Nd-YAG laser photodisruption may be employed in special cases in which thick, fresh blood is trapped beneath the internal limiting membrane13 or behind the posterior hyaloid.14 Blood in these anatomic locations does not itself cause damage to the retina, but it may limit central vision, and it may prevent the clinician from identifying underlying retinal pathology. Photodisruption results in a localized concussive effect that breaks open the posterior hyaloid or internal limiting membrane. If the trapped blood has not yet solidified, it may then be allowed to “spill out” through the opening into the vitreous cavity (Fig. 5). Risks of this technique include damage to the underlying retina if the laser treatment is applied too close to the retina or if the blood is not thick enough to absorb the concussive effect.
Pneumatic displacement of hemorrhage has been successfully employed in select cases of submacular hemorrhage from a macroaneurysm (Fig. 6). Subretinal blood results in irreversible damage to photoreceptors within 7 days.15–17 Many surgeons attempt to remove or at least displace this blood within 2 weeks and preferably within 7 days in an attempt to preserve central vision. A proposed alternative to vitrectomy with surgical evacuation of the blood is pneumatic displacement, in which a bubble of perfluorocarbon gas is injected into the vitreous cavity. The patient's head is then positioned such that the bubble's buoyant force squeezes the subretinal blood out of the macula and into the inferior fundus.18 Some surgeons precede the gas bubble with an intravitreal injection of tissue plasminogen activator (TPA) in order to lyse the blood clot; whether or not the TPA reaches the blood clot in sufficient quantities to cause an appreciable lysing effect is controversial.19 There is histological evidence that this technique in some cases causes shearing of the photoreceptor outer segments during the pneumatic displacement procedure.20
Vitrectomy with surgical evacuation of submacular hemorrhage may be indicated when there is a reasonable chance of recovery of some degree of central vision (Fig. 7).21–26 In the eye in which blood that has been under the macula for more than 2 weeks, there is little possibility of visual recovery because of blood toxicity to the photoreceptors. Many authorities consider surgical evacuation of submacular blood when the blood has been present under the macula for 2 weeks or less, preferably less than 7 days. The technique involves a pars plana vitrectomy, followed by a small perforation near the edge of the blood to gain access to the subretinal space. TPA is usually employed to help lyse the blood, thus facilitating its removal with minimal damage to the photoreceptors. The blood is removed using a subretinal cannula; some models feature a double-barreled shaft that allows the injection of fluid into the subretinal space through one barrel and the removal of blood through the other barrel. Some authors note that the use of a bubble of perfluorocarbon liquid on the surface of macula helps express the blood from beneath the macula.
|Retinal arterial macroaneurysms are relatively large outpouchings of a retinal artery associated with systemic hypertension and atherosclerosis. They are often asymptomatic and require no treatment. However, if they produce exudation or hemorrhage that affects or threatens central visual acuity, treatment options include laser photocoagulation, Nd-YAG laser photodisruption, pneumatic displacement of subretinal hemorrhage, and vitrectomy with surgical evacuation of subretinal hemorrhage.|
19. Hassan AS, Johnson MW, Schneiderman TF, et al: Management of submacular hemorrhage with intravitreal tissue plasminogen activator injection and pneumatic displacement. Ophthalmology 106:1900, 1999.