Page's kidney is a condition that occurs due to external renal compression, usually caused by a subcapsular haematoma, generating a renal compartmental syndrome with parenchymal damage and renal perfusion alteration. Classically associated with renal trauma, Page's kidney can also arise after invasive renal procedures, such as renal biopsies or percutaneous nephrostomies. Clinically, it can trigger hypertension due to activation of the renin-angiotensin system induced by hypoperfusion secondary to renal parenchymal compression and can also present with varying degrees of renal function impairment. Furthermore, severe acute renal failure may be found particularly in patients with solitary kidneys or renal transplants. We present two cases of Page's kidney after renal biopsy and their PoCUS ultrasound findings. We would like to highlight the reversed diastolic flow on Doppler ultrasound in this entity, a pattern we have found in all two cases.

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.

The compression of the renal parenchyma due to a subcapsular hematoma, also known as the "Page kidney," is a potentially serious but treatable complication of renal biopsy. Hypertension is very common and, in some cases, renal failure may be present. In kidney transplantation, it is a not well-described entity. Rapid intervention is essential to avoid irreversible damage of the graft and preserve its function. We report 2 cases of acute renal failure due to Page kidney in patients with renal transplant after a percutaneous biopsy with successful recovery after surgical treatment. In addition, we conducted a literature review in order to describe the clinical characteristics of this infrequent complication in patients with a history of renal transplant.

We report a rare case of allograft loss from acute Page kidney secondary to trauma that occurred 12 years after kidney transplantation. A 67-year-old Caucasian male with a past surgical history of kidney transplant presented to the emergency department at a local hospital with left lower abdominal tenderness. He recalled that his cat, which weighs 15 lbs, jumped on his abdomen 7 d prior. On physical examination, a small tender mass was noticed at the incisional site of the kidney transplant. He was producing a normal amount of urine without hematuria. His serum creatinine level was slightly elevated from his baseline. Computer tomography revealed a large subscapular hematoma around the transplant kidney. The patient was observed to have renal trauma grade II at the hospital over a period of three days, and he was finally transferred to a transplant center after his urine output significantly decreased. Doppler ultrasound demonstrated an extensive peri-allograft hypoechoic area and abnormal waveforms with absent arterial diastolic flow and a patent renal vein. Despite surgical decompression, the allograft failed to respond appropriately due to the delay in surgical intervention. This is the third reported case of allograft loss from acute Page kidney following kidney transplantation. This case reinforces that kidney care differs if the kidney is solitary or a transplant. Early recognition and aggressive treatments are mandatory, especially in a case with Doppler signs that are suggestive of compression.