Paul B. Greenberg, MD · Adam Martidis, MD

Introduction

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Retinal arterial macroaneuryms (RAMs) are acquired vascular dilatations located mainly at the arterial bifurcations on the first three orders of the arterial tree (Slide 1A and Slide 1B). RAMs occur most commonly in women between the ages of 60 and 80 years. Many patients with RAMs have hypertension, generalized atherosclerotic disease, and serum lipid abnormalities. Visual loss typically stems from hemorrhage in various layers of the retina and vitreous, or macular exudation and edema. The most effective treatment for RAMs still remains to be elucidated.

Pathophysiology

The pathogenesis of an RAM is incompletely understood. With aging, the arterial walls become less elastic as both the medial muscle fibers and intima are gradually replaced by collagen. This decrease in elasticity renders the arterioles more susceptible

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to dilatation from elevated hydrostatic pressure. Hypertensive patients who have elevated hydrostatic pressure, decreased autoregulation, and hyaline degeneration of the arterial walls are at particular risk. Although these processes predispose patients to the formation of RAMs, the cause of the focal arteriolar wall disease remains unclear. Proposed inciting factors include an embolic event or occlusive disease with localized thrombosis.

Clinical Features

Most symptomatic patients with an RAM present with acute loss of vision. Up to 86% of patients will present with one RAM; the rest of patients present with two or more (Slide 2). Most RAMs have a round,

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saccular, or fusiform appearance and occur in the superior temporal quadrant. One-third of cases will have vitreous hemorrhage and/or macular exudate, edema, and hemorrhage; 10% will have visible retinal emboli. Often, retinal exudates form a circinate pattern around the RAM (Slide 3A and Slide 3B). Hemorrhages can occur in the vitreous cavity or subhyaloid, subinternal limiting membrane, and intraretinal and subretinal spaces (Slide 4A and Slide 4B). The term hourglass hemorrhage has been used to describe simultaneous preretinal and subretinal hemorrhages. An RAM can grow as large as 2 disc diameters, though it will generally rupture before reaching this size. Ten percent of RAMs are pulsatile at the time of presentation, though the clinical significance of this finding is unclear.

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Differential Diagnosis

The differential diagnosis of an RAM includes tumors, such as retinal capillary hemangioma, retinal cavernous hemangioma or malignant melanoma, ocular granuloma, retinal telangiectasia, retinal vein occlusion (including venous macroaneurysms), diabetic retinopathy, and age-related macular degeneration. Although characteristic ophthalmoscopic and angiographic findings will typically distinguish RAM from these other lesions, the presence of extensive hemorrhage can make the diagnosis more challenging.

Diagnostic Testing

When not obscured by hemorrhage, fluorescein angiography demonstrates uniform filling of the RAM. Leakage may occur proximal to or at the site of an RAM. The involved arteriole is typically narrowed and areas of capillary abnormalities and nonperfusion are often adjacent to an RAM. Cystoid macular edema can also be seen. Indocyanine green (ICG) angiography can be useful in identifying RAMs associated with hemorrhages that obscure visualization by ophthalmoscopy or fluorescein angiography. An ICG stain transmits 57% of light and a sodium fluorescein stain transmits 4% through a 100-µm layer of blood. In addition, the higher protein binding capacity of ICG (98%) compared to fluorescein (60%) results in less dye leakage and consequently more well-defined images.

Natural History

After remaining stationary for long periods, most RAMs eventually undergo thrombosis, fibrosis, and spontaneous involution. Visual prognosis can vary depending upon the location and size of macular hemorrhages, exudation, and edema, though many eyes will return to the baseline visual acuity. Brown and colleagues retrospectively analyzed 26 untreated eyes with RAMs for 3 years and found that compared to baseline, 50% of eyes had improved by two or more lines of visual acuity, 35% remained unchanged, and 15% had decreased visual acuity. Structural damage from chronic macular edema and exudate is the most common cause of poor vision in eyes with RAMs.

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Most vitreous, preretinal and intraretinal hemorrhages will resolve over several months (Slide 5A and Slide 5B), though secondary epiretinal membranes can leave patients with residual metamorphopsia or distortion. Subretinal hemorrhages pose a greater visual threat. Animal studies have suggested that irreversible damage to photoreceptor and retinal pigment epithelial cells can occur after 2 weeks, leading to permanent loss of central vision. In Brown’s natural history study, subretinal hemorrhage was a significant risk factor for visual acuity of 20/80 or worse.

Treatment

The treatment of RAMs remains controversial. Many experts have advocated focal laser photocoagulation for visual acuity loss secondary to macular edema and exudation. This usually consists of direct photocoagulation of the RAM and/or perianeurysmal area. However, the benefits of the laser treatment are unclear. Brown and colleagues found no treatment benefit in eyes that received direct photocoagulation of RAMs compared to a matched control group. In addition, several eyes developed arteriolar occlusions after receiving photocoagulation. The investigators recommended observation for most patients. It is unclear if perianeurysmal laser treatment alone would be more efficacious.

The management of large hemorrhages is also complicated by the lack of randomized, controlled studies. Photodisruption with Nd:YAG lasers for RAMs with preretinal hemorrhages may be considered in cases requiring more rapid visual rehabilitation. Visual recovery usually occurs within 1 week, though the technique is not effective in eyes with subretinal hemorrhage. For these cases, pneumatic displacement (e.g., with perfluoropropane gas) or pars plana vitrectomy with or without tissue plasminogen activator (tPA) may be clinically useful, especially in the first 2 weeks of visual loss.

References

Brown DM, Sobol WM, Folk JC, et al. Retinal arterial macroaneurysms: Long-term visual outcome. Br J Ophthalmol. 1994;78:534-538.

Gomez-Ulla F, Gonzalez F, Torreiro MG, et al. Indocyanine green angiography in isolated primary retinal arterial macroaneurysms. Acta Ophthalmol Scand. 1998;76:671-674.

Humayun M, Lewis H, Flynn HW, et al. Management of submacular hemorrhage associated with retinal arterial macroaneurysms. Am J Ophthalmol. 1998;126:358-361.

Iijima H, Satoh S, Tsukahara S. Nd:YAG laser photodisruption for preretinal hemorrhage due to retinal macroaneurysm. Retina. 1998;18:430-434.

Kyoko O-M, Hayano M, Futagami S, et al. Spontaneous involution of a large retinal arterial macroaneurysm. Acta Ophthalmol Scand. 2000;78:114-117.

Ohji M, Saito Y, Hayashi A, et al. Pneumatic displacement of subretinal hemorrhage without tissue plasminogen activator. Arch Ophthalmol. 1998;116:1326-1332.

Rabb MF, Gagliano DA, Teske MP. Retinal arterial macroaneurysms. Surv Ophthalmol. 1988;33:73-96.

Zhao P, Hayashi H, Oshima K, et al. Vitrectomy for macular hemorrhage associated with retinal arterial macroaneurysm. Ophthalmology. 2000;107;613-617.