A 58-year-old man with poorly controlled hypertension presents with sudden painless loss of superior visual field in the right eye. Fundoscopy reveals the pattern shown in the diagram, with the structure marked **A** (sectoral flame-shaped hemorrhages along venous distribution) confined to the superotemporal quadrant. Which of the following best explains why the superotemporal quadrant is most frequently involved in this condition?

Explanation

## Why "Highest density of arteriovenous crossings in the superotemporal region" is right The clinical anchor states that the superotemporal quadrant is involved in 60–70% of BRVO cases specifically because this region has the HIGHEST density of arteriovenous (AV) crossings. At these crossings, the artery and vein share a common adventitial sheath. Atherosclerotic thickening of the artery compresses the underlying vein at these sites, leading to turbulent flow, endothelial damage, and thrombus formation. The anatomical predisposition to AV crossing compression in the superotemporal region directly explains the sectoral flame-shaped hemorrhages marked **A** in this patient's fundus. ## Why each distractor is wrong - **Greater arterial perfusion pressure in the superotemporal quadrant**: While systemic hypertension is the single most important risk factor (present in 65% of BRVO cases), the specific anatomical reason for superotemporal predominance is not differential perfusion pressure but rather the density of AV crossings. Perfusion pressure is systemic, not region-specific. - **Preferential atherosclerotic plaque deposition in superotemporal vessels**: Although atherosclerotic thickening of the artery is the mechanism of vein compression, there is no evidence that atherosclerosis preferentially deposits in the superotemporal region. The high frequency in this quadrant is explained by the higher number of AV crossing sites, not selective atherosclerotic targeting. - **Anatomically longer venous drainage pathway in the superotemporal quadrant**: The superotemporal quadrant does not have a longer drainage pathway than other regions. The anatomical difference is the density of AV crossings, not the length of venous drainage. **High-Yield:** BRVO superotemporal predominance (60–70%) = highest density of AV crossings in this region; artery compresses vein at shared adventitial sheath → turbulent flow → thrombosis. [cite: AAO BCSC Section 12: Retina and Vitreous]