A 45-year-old man presents with acute left flank pain radiating to the groin. Ultrasound of the abdomen shows left-sided hydronephrosis. The structure marked **A** in the diagram demonstrates severe dilation with blunted calyces and communicates with a markedly thinned renal parenchyma (structure **B**). This imaging appearance corresponds to SFU Grade 4 hydronephrosis. Which of the following best explains the pathophysiological mechanism underlying the parenchymal thinning observed in this grade?