Retinal Arterio-Arterial Collaterals in Susac Syndrome: A Case Report

Background : Susac syndrome (SS) is a rare autoimmune endotheliopathy characterized by the clinical triad of encephalopathy, branch retinal artery occlusion (BRAO), and sensorineural hearing loss. The development of retinal arterial collaterals in this condition is infrequently documented, and long-term angiographic findings during recurrence are not well characterized. Case Presentation : A 35-year-old Chinese woman presented with acute, painless monocular vision loss in the right eye (RE). Multimodal imaging revealed BRAO with retinal edema and notably, pre-existing retinal arterio-arterial (A-A) collaterals in the temporal retina. Fluorescein angiography (FA) demonstrated characteristic arterial wall hyperfluorescence (AWH) in both eyes. Cranial magnetic resonance imaging (MRI) showed rounded hyperintense lesions in the cerebral white matter, and audiometry confirmed bilateral low-frequency sensorineural hearing loss, fulfilling the classic diagnostic triad for SS. The patient responded favorably to high-dose intravenous corticosteroids. After a four-year period of quiescence, she experienced a disease relapse manifesting as recurrent vision loss in the RE and headache. Notably, while cranial MRI remained stable, repeat FA revealed new areas of AWH in the RE and the complete resolution of the previously noted A-A collaterals. Conclusions : This case highlights two rare angiographic observations in SS: the presence of established A-A collaterals at initial diagnosis and their subsequent regression with disease recurrence, alongside new AWH in the absence of radiographic progression. Our findings underscore the critical role of FA as a sensitive biomarker for detecting subclinical disease reactivation in SS, even when neuroimaging is unremarkable. Long-term ophthalmic follow-up with serial FA is essential for monitoring disease activity and guiding management in these patients.