Clinical description

Acquired retinal macroaneurysms are fusiform or round dilations of the retinal arterioles that occur in the posterior fundus within the first three orders of arteriolar bifurcation. Often they are located at the site of an arteriolar bifurcation or an arteriovenous crossing (Fig. 52.1). The supratemporal artery is the most commonly reported site of involvement because patients with such involvement are more likely to have visual impairment. Women make up the majority of reported cases. Most cases are unilateral, while 10% may be bilateral. Retinal macroaneurysm was estimated to occur in 1 in 9000 in the Beijing Eye Study.¹

Fig. 52.1 (A) A 62-year-old woman with hypertension had a subretinal hemorrhage associated with a macroaneurysm in her left supratemporal artery. (B) The fluorescein angiogram demonstrated hypofluorescence from blockage from the retinal hemorrhage and hyperfluorescence of the retinal macroaneurysm itself, apparent as a round dilation located at the arteriolar bifurcation.

Most commonly, retinal macroaneurysm affects patients in the sixth and seventh decades of life. Often associated are vascular problems such as hypertension and general arteriosclerotic cardiovascular disease, as noted by Robertson,² who first coined the term retinal macroaneurysm. Uncontrolled hypertension can present with a retinal artery macroaneurysm and its accompanying vitreous hemorrhage.³ Other investigators have confirmed this association with hypertension.⁴ Serum lipid and lipoprotein abnormalities have also been reported in patients with this condition.⁵ Systemic investigations for hypertension and cardiovascular disease should be conducted in patients who have a retinal arteriolar macroaneurysm.

Although a patient with a retinal arteriolar macroaneurysm may be asymptomatic if the macula is not involved (Fig. 52.2), the most common clinical symptom is decline in central visual acuity as a result of retinal edema, exudation, or hemorrhage.⁶ Bleeding from macroaneurysms can occur in the subretinal space, into the retina, beneath the internal limiting membrane, or into the vitreous. So-called hourglass hemorrhages are typical. Hemorrhage in the space beneath the retinal pigment epithelium may produce a dark lesion simulating an ocular tumor such as malignant melanoma,⁷ or a lesion associated with age-related macular degeneration. A complication of the vitreous hemorrhage also includes the development of angle closure glaucoma.⁸

Fig. 52.2 (A) The retinal hemorrhage superior to the optic disc, associated with a retinal macroaneurysm, caused no ocular symptoms. (B) Six months later, the retinal macroaneurysm is partially obstructed by the resolving retinal hemorrhage, with a surrounding ring of lipid. (C) Eight months later, the macroaneurysm has spontaneously involuted, with complete resolution of the hemorrhage and a decrease in the lipid.

The hemorrhage may also partially or completely obscure the aneurysm (Fig. 52.3). Occasionally, multiple macroaneurysms occur. Other retinal microvascular changes associated with macroaneurysms include widening of the periarterial capillary-free zone around the area of the aneurysm, capillary dilation and nonperfusion, microaneurysms, and artery-to-artery collaterals.

Fig. 52.3 (A) A preretinal hemorrhage partially obscures the retinal macroaneurysm. (B) The fluorescein angiogram shows the hyperfluorescence that corresponds to the hemorrhage and the hyperfluorescence of the retinal macroaneurysm. (C) At 20 months later, there is spontaneous resolution of the hemorrhage and the retinal macroaneurysm.

Diagnosis of retinal macroaneurysm

Fluorescein angiography initially may fail to demonstrate the macroaneurysm because of blockage by the surrounding hemorrhage. Dense hemorrhage in the retina can cause marked hypofluorescence. In such cases of dense hemorrhage, indocyanine green angiography may be useful because its absorption and emission peak in the near-infrared range allow the light to penetrate the hemorrhage to a greater extent than fluorescein angiography.⁹ A small case series using indocyanine green angiography has demonstrated these lesions to be pulsatile and contiguous with the arterial wall, pathognomonic of an insolated retinal artery macroaneurysm.¹⁰ The macroaneurysm typically fills in the early arterial phase of the angiogram. The appearance of the late phase of the fluorescein angiogram varies, ranging from little staining of the vessel wall to marked leakage. Leakage of surrounding dilated capillaries also may be seen. The lipid often present in the macular area fails to block fluorescein unless the amount of lipid is massive. Macular hole formation following rupture of a retinal arterial macroaneurysm has been reported.^11,12

Histopathologic studies of macroaneurysms have shown gross distension of the involved retinal arteriole. Surrounding this are fibroglial proliferation, dilated capillaries, extravasated blood, lipoidal exudates, and hemosiderin deposits.

Evaluation of the retinal structure with optical coherence tomography was conducted in a series of patients with retinal macroaneurysm.¹³ Although most of the retinal structure was intact at the initial exam, subretinal hemorrhage or extensive exudative changes from retinal macroaneurysm can cause the deterioration of the foveal outer photoreceptor layer with a poor visual outcome.

Natural course and treatment of retinal macroaneurysms

Several series have reported on the natural history and treatment response of macroaneurysms.^5,14,15 The yellow dye laser has been considered for treatment because of its theoretical advantages.¹⁶ Some investigators believe the visual prognosis is excellent in most patients who have macroaneurysms and do not have treatment because the lesions can thrombose and undergo spontaneous involution with clearing of the macular exudate.² However, the exudative process may progress in some patients and cause structural damage to the macula with loss of vision (Fig. 52.4).¹⁷ Moderate visual loss also may occur if bleeding causes secondary morphologic changes in the macula. No clear indication for treatment with laser photocoagulation has been established, and the beneficial effects of such treatments have not been proven.

Fig. 52.4 (A) The retinal macroaneurysm caused a progressive increase in the retinal hard exudate, resulting in a visual acuity decrease to 20/25 in the right eye over a period of 22 months. (B) The edema and lipid were threatening the macula. The patient was offered treatment.

Vitrectomy was performed for clearing the macular hemorrhage associated with the rupture of a macroaneurysm.¹⁸ The results of vitrectomy are variable depending on the location of the hemorrhage from the retinal macroaneurysms. The vision is particularly poor in those patients who have dense submacular hemorrhage.¹⁹

Pneumatic displacement with or without tissue plasminogen activator has also been used for the therapy of submacular hemorrhage associated with a macroaneurysms.²⁰ Yag laser has also been used to treat such premacular hemorrhage.²¹ The surgical excision of the retinal macroaneruysm with scissors and diathermy followed by the drainage of the submacular hemorrhage was also explored in 2 cases, with some improvement in vision.²²

Many investigators consider direct laser photocoagulation of the macroaneurysm if the lipid exudate coming from it threatens the fovea. Treatment when hemorrhage is present is fraught with difficulties. There is also the danger of occluding the retinal arteriole during treatment. This potential complication must always be considered when the distal portion of the arteriole being considered for treatment supplies the macula.

The differential diagnoses of retinal macroaneurysms include other retinal vascular abnormalities, including diabetic retinopathy, retinal telangiectasia, retinal capillary angioma, cavernous hemangioma, malignant melanoma,⁷ and the hemorrhagic pigment epithelial detachment of age-related macular degeneration.²³