A 48-year-old woman presented with hyperreninemic hypertension and renal dysfunction and was diagnosed with hydronephrosis-related Page kidney. The pathophysiology was “renal tamponade”, in which the kidney was compressed by the renal pelvis and Gerota’s fascia, resulting in intrarenal microvascular ischemia. Ureteral stent placement promptly improved the hyperreninemic hypertension and renal dysfunction, and additional perirenal fluid drainage gradually improved these conditions. These observations indicated the following three points. First, renal compression-induced renin–angiotensin–aldosterone system upregulation plays an important role in the pathogenesis of Page kidney. Second, physicians should consider perirenal fluid drainage as a therapeutic option in addition to ureteral stenting in patients with hydronephrosis-related Page kidney. Third, bilateral perirenal subcapsular hematomas in this case could be caused by hydronephrosis. Hydronephrosis-induced intrarenal pressure elevation possibly caused chronic perirenal subcapsular hemorrhage at the vulnerable sites of the renal cortex and peeling of the renal capsule from the cortex, resulting in the bilateral massive subcapsular hematomas and Page kidney.
