A 5-year-old boy presents with leukocoria detected on routine examination. Fundoscopy reveals yellow subretinal exudates and bulbous, dilated, tortuous vessels in the temporal periphery. The structure marked **B** in the diagram shows the characteristic appearance of Coats disease with telangiectasia and exudation. Which of the following best describes the underlying pathophysiological mechanism responsible for the progressive exudation seen in this condition?
A. Retinal pigment epithelium dysfunction leading to impaired phagocytosis of photoreceptor outer segments
B. Breakdown of the blood-retinal barrier due to abnormal endothelial cells in retinal vessels
C. Persistent fetal vasculature with incomplete regression of hyaloid artery branches
Vitreous hemorrhage from fragile neovascular membranes at the vitreoretinal interface
D.
Explanation
Why "Breakdown of the blood-retinal barrier due to abnormal endothelial cells in retinal vessels" is right
Coats disease is fundamentally characterized by a breakdown of the blood-retinal barrier at the level of abnormal endothelial cells in retinal vessels. This defect allows lipid and protein leakage from the telangiectatic and aneurysmal vessels, resulting in the progressive intra-retinal and subretinal lipid exudation that defines the disease. Somatic mutations in the NDP gene (encoding Norrin, which signals through FZD4/LRP5) have been implicated in some cases, further supporting the endothelial dysfunction mechanism. This is the pathophysiological cornerstone of Coats disease and directly explains why the exudates are rich in cholesterol (visible as cholesterol clefts on OCT).
Why each distractor is wrong
Retinal pigment epithelium dysfunction leading to impaired phagocytosis of photoreceptor outer segments: This mechanism is characteristic of age-related macular degeneration and inherited retinal dystrophies, not Coats disease. RPE dysfunction does not explain the vascular telangiectasias or the acute exudative process seen in Coats disease.
Vitreous hemorrhage from fragile neovascular membranes at the vitreoretinal interface: While vitreous hemorrhage can occur as a late complication of Coats disease, it is not the primary mechanism of exudation. The exudation in Coats disease originates from the retinal vasculature itself, not from neovascular membranes, and the yellow subretinal exudate is lipid-rich, not hemorrhagic.
Persistent fetal vasculature with incomplete regression of hyaloid artery branches: This describes the pathophysiology of familial exudative vitreoretinopathy (FEVR, marked C in the diagram) and retinopathy of prematurity (ROP, marked A), not Coats disease. While FEVR and Coats disease can both present with exudation, FEVR is hereditary and associated with mutations in genes encoding Wnt signaling components, whereas Coats disease is idiopathic and nonhereditary.
High-YieldNEET PG
Coats disease = idiopathic, nonhereditary, unilateral (>90%), male-predominant (M:F 10:1) retinal vascular disorder with blood-retinal barrier breakdown at abnormal endothelial cells → lipid exudation; presents as painless leukocoria in first decade (mean age 5 years); telangiectasias and "light-bulb" aneurysms in temporal periphery; yellow subretinal exudate with cholesterol clefts on OCT; treated with laser photocoagulation ± cryotherapy ± anti-VEGF.
AAO BCSC Section 6 — Pediatric Ophthalmology 2023; Shields JA et al, Curr Opin Ophthalmol 2001
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