Branch Retinal Artery Occlusion Differential Diagnosis: Key Distinctions for Accurate Diagnosis

INITIAL PRESENTATION: Recognizing BRAO

The sudden onset of visual disturbances can be alarming for patients and challenging for clinicians to diagnose accurately. Branch retinal artery occlusion (BRAO), while less common than central retinal artery occlusion (CRAO), is a critical condition that demands prompt recognition due to its implications for systemic vascular health, particularly stroke risk. A 61-year-old woman’s case vividly illustrates the typical presentation of symptomatic BRAO. She experienced a sudden blurring of vision in her right eye, accompanied by a significant constriction of her inferior visual field while showering. Although she denied weakness or numbness, her husband noted unsteadiness. Initial emergency room evaluation, including a CT angiogram, suggested right vertebral artery obstruction, leading to further investigation at a stroke center. This case underscores the importance of considering BRAO in patients presenting with acute visual loss, particularly those with vascular risk factors.

Her medical history, significant for transient ischemic attack (TIA), type 2 diabetes mellitus, and a history of smoking, placed her at increased risk for vascular events. Ocular examination revealed preserved visual acuity at 20/20-2 in the affected right eye, but with a notable relative afferent pupillary defect (RAPD) and a near-total inferior nasal visual field deficit. Funduscopy was crucial, revealing an embolus lodged in a branch of the superior retinal arcade, confirming BRAO. Fundus photography (Figure 1), visual field testing (Figure 2), and optical coherence tomography (OCT) (Figure 3) further documented the retinal findings and visual field defect. The initial differential diagnosis considered a range of conditions including central retinal artery occlusion (CRAO), arteritic and non-arteritic anterior ischemic optic neuropathy (AAION and NAION), and acute retinal necrosis. This highlights the necessity for a comprehensive differential diagnosis in cases of acute vision loss.

BRANCH RETINAL ARTERY OCCLUSION DIFFERENTIAL DIAGNOSIS: Distinguishing Key Conditions

When faced with a patient presenting with acute, painless vision loss, particularly monocular, a clinician must systematically consider various potential diagnoses. The differential diagnosis for branch retinal artery occlusion (BRAO) includes several critical conditions that, while sharing some overlapping symptoms, possess distinct characteristics crucial for accurate differentiation. These primarily include central retinal artery occlusion (CRAO), arteritic anterior ischemic optic neuropathy (AAION), non-arteritic anterior ischemic optic neuropathy (NAION), and acute retinal necrosis (ARN). Understanding the nuances of each condition is paramount for timely and appropriate management.

Central Retinal Artery Occlusion (CRAO) vs. BRAO

Both CRAO and BRAO are caused by blockages in the retinal arteries, predominantly due to emboli. However, the location and extent of the occlusion differ significantly, leading to variations in clinical presentation.

Vessel Occlusion: CRAO involves the main central retinal artery, causing widespread retinal ischemia. BRAO, conversely, affects a branch of the central retinal artery, resulting in ischemia localized to the area supplied by that specific branch.
Visual Acuity Impact: CRAO typically leads to profound vision loss, often to the level of counting fingers or worse. In contrast, BRAO often spares central vision if the macula is not directly affected, and visual acuity may be relatively preserved (20/40 or better in many cases), as seen in the presented case. The visual field defect in BRAO is typically sectoral or altitudinal, corresponding to the affected arterial branch, whereas CRAO causes a more global visual field constriction.
Fundoscopic Findings: In both CRAO and BRAO, retinal whitening (opacification) is a key finding due to retinal edema in the ischemic area. However, in CRAO, this whitening is often diffuse and involves the posterior pole, sometimes with a “cherry-red spot” in the macula due to the preserved choroidal circulation contrasting with the pale, ischemic retina. In BRAO, the retinal whitening is sectorial, confined to the distribution of the occluded branch artery. Emboli, such as Hollenhorst plaques (cholesterol emboli), platelet-fibrin emboli, or calcific emboli, may be visible in both conditions, pinpointing the site of occlusion.

Arteritic Anterior Ischemic Optic Neuropathy (AAION) vs. BRAO

AAION is a form of optic neuropathy caused by inflammation and occlusion of the posterior ciliary arteries, often associated with giant cell arteritis (GCA). Distinguishing AAION from BRAO is critical because GCA requires immediate high-dose steroid treatment to prevent irreversible vision loss and systemic complications.

Pathophysiology: AAION is inflammatory and affects the optic nerve head primarily, while BRAO is embolic or thrombotic and affects the retinal arteries.
Age and Systemic Symptoms: AAION, especially due to GCA, is more common in older individuals (typically over 50 years) and may present with systemic symptoms like headache, scalp tenderness, jaw claudication, and muscle aches (polymyalgia rheumatica). BRAO, while more common in older adults with vascular risk factors, does not typically present with these systemic inflammatory symptoms.
Visual Loss Characteristics: Both AAION and BRAO cause sudden vision loss. In AAION, vision loss can range from mild to severe and is often altitudinal. BRAO also causes sudden vision loss, but as discussed, it’s often less severe than CRAO and sectoral.
Optic Disc Appearance: In AAION, the optic disc is often swollen and pale (“chalky white”) acutely. In BRAO, the optic disc may be normal, although optic atrophy can develop later in both conditions. The key differentiating fundoscopic finding in BRAO is the retinal whitening and potential visible embolus in a retinal artery, which are not features of AAION.
ESR and CRP: Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are strong indicators of GCA and AAION, and should be checked urgently in suspected cases of AAION, particularly in older patients. These inflammatory markers are not typically elevated in BRAO.

Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION) vs. BRAO

NAION is the more common form of anterior ischemic optic neuropathy and is not associated with systemic arteritis. Differentiating NAION from BRAO is important for prognosis and management.

Pathophysiology: NAION is thought to be caused by hypoperfusion of the optic nerve head, often in the setting of “disc at risk” (small cup-to-disc ratio). BRAO, again, is due to retinal artery occlusion.
Risk Factors: NAION is associated with vascular risk factors similar to BRAO (hypertension, diabetes, hyperlipidemia) but also with sleep apnea and certain medications like amiodarone and phosphodiesterase-5 inhibitors.
Visual Field Defect: NAION often presents with an altitudinal visual field defect, similar to some presentations of BRAO. However, NAION defects are more commonly inferior altitudinal, while BRAO defects are dictated by the branch artery involved.
Optic Disc Appearance: In acute NAION, optic disc edema is a hallmark finding, though it may be subtle. In BRAO, the optic disc is typically normal initially, unless there is concomitant optic nerve involvement, which is not typical of isolated BRAO. The retinal whitening and potential embolus seen in BRAO are absent in NAION.
RAPD: Both NAION and BRAO can present with a relative afferent pupillary defect (RAPD) in the affected eye. RAPD is therefore not a differentiating factor between these two conditions.

Acute Retinal Necrosis (ARN) vs. BRAO

Acute retinal necrosis (ARN) is a viral retinitis, usually caused by herpes simplex virus or varicella-zoster virus, that can cause retinal ischemia and vision loss. While less likely to be initially confused with BRAO, considering ARN in the differential is important, particularly if there are inflammatory signs.

Etiology: ARN is infectious and inflammatory, while BRAO is vascular and embolic/thrombotic.
Associated Symptoms: ARN is often associated with pain in or around the eye, anterior uveitis (cells and flare in the anterior chamber), and vitritis (inflammatory cells in the vitreous). BRAO is typically painless and without anterior segment inflammation or significant vitritis initially.
Fundoscopic Findings: In ARN, retinal necrosis appears as peripheral retinal whitening with indistinct borders, often progressing posteriorly. Vascular occlusions can occur in ARN as a secondary phenomenon due to inflammation, but the primary finding is retinal necrosis and inflammation, not an arterial embolus. BRAO is characterized by sectorial retinal whitening along an arterial distribution and a potential visible embolus.
Progression and Bilaterality: ARN can be rapidly progressive and can become bilateral, especially in immunocompromised individuals. BRAO is typically a singular, acute event, and bilateral simultaneous BRAO is very rare.

CLINICAL COURSE AND MANAGEMENT IMPLICATIONS

In the presented case, the diagnosis of BRAO was confirmed by the fundoscopic finding of an embolus and sectorial retinal whitening, supported by visual field testing and OCT. Because the symptom onset was greater than 18 hours prior to evaluation, acute ophthalmic interventions to dislodge the embolus were not initiated, as the window for potential benefit is limited to within the first few hours of onset. The patient was appropriately started on secondary stroke prevention measures including aspirin, clopidogrel, and atorvastatin. The recommendation for stent-assisted angioplasty by interventional neurology reflects the systemic vascular implications of symptomatic BRAO, particularly in the context of significant carotid stenosis.

The crucial takeaway for clinicians is that symptomatic BRAO is a stroke equivalent. Prompt referral to a stroke center for comprehensive vascular evaluation is essential to identify and manage underlying carotid artery disease, cardiac emboligenic sources, and other systemic vascular risk factors. While immediate ophthalmic treatments for BRAO are of limited proven efficacy, aggressive management of systemic vascular risk factors and secondary stroke prevention are paramount to reduce the risk of future stroke and cardiovascular events. Recognizing the differential diagnoses of acute vision loss, and accurately distinguishing BRAO from conditions like CRAO, AAION, NAION, and ARN, is the first critical step in ensuring appropriate and timely patient care, extending beyond ocular health to encompass overall systemic well-being.

References

(References are identical to the original article and are thus omitted here for brevity, but would be included in a complete, rewritten article.)