Acute Tubular Necrosis - Hypotensive Kidneys

A 65-year-old man undergoes emergency repair of a ruptured abdominal aortic aneurysm. Intraoperatively, his mean arterial pressure drops to 50 mmHg and remains <55 mmHg for 6 hours. Postoperatively, he develops oliguria with serum creatinine rising from 1.0 to 3.2 mg/dL within 48 hours. Urinalysis shows muddy-brown granular casts and renal tubular epithelial cells; urine sodium is 45 mmol/L and FENa is 3.5%. At autopsy, both kidneys show the gross appearance depicted in the diagram. The structure marked **A** (pale, swollen cortex) reflects ischemic injury predominantly affecting which tubular segment?