What causes the Page kidney appearance on CT of the abdomen?
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Answer:
Page kidney is the combination of a chronic subcapsular collection compressing the renal parenchyma and secondary hypertension. On CT the kidney is deformed and flattened by a crescentic subcapsular collection that indents the parenchyma rather than displacing the kidney, which is the feature that distinguishes a subcapsular from a perinephric collection, since a perinephric haematoma spreads within Gerota fascia and does not compress the renal contour. The usual causes are blunt trauma, including sporting injury, renal biopsy, extracorporeal shock wave lithotripsy, anticoagulation, a ruptured cyst or angiomyolipoma, and it is a recognised complication after renal transplantation, where the low-pressure iliac fossa position and immunosuppression contribute. Attenuation of the collection depends on its age, and MRI is useful for dating haemorrhage and for characterising a chronic organised collection or a urinoma. The clinical importance is that the hypertension is renin-mediated and potentially curable: recognition should prompt renin-angiotensin blockade and consideration of drainage, capsulectomy or, occasionally, nephrectomy in a chronically non-functioning kidney, while in the transplant setting prompt decompression can rescue graft function. The differential includes renal artery stenosis, which also causes renin-mediated hypertension but with a different vascular appearance, and renal vein thrombosis.
Why is it called so?
The condition is named after Irvin Page, who produced hypertension experimentally by wrapping kidneys in cellophane and compressing them.
Pathophysiology
Blood or fluid trapped between the renal capsule and the parenchyma cannot expand outward because the capsule is inelastic, so pressure is transmitted inward and compresses the renal cortex. The compressed parenchyma is rendered ischaemic, which reduces perfusion pressure sensed at the juxtaglomerular apparatus and triggers renin release. Angiotensin II generation causes vasoconstriction and aldosterone-mediated sodium retention, so systemic blood pressure rises, exactly reproducing the two-kidney one-clip Goldblatt mechanism. If the compression persists, the affected kidney becomes progressively atrophic and fibrotic, which is why early decompression can normalise blood pressure whereas long-standing cases may not respond.
Alternative names: Page phenomenon; subcapsular haematoma with hypertension
Other associated named signs: Rim nephrogram of chronic compression and the flattened kidney sign of a subcapsular collection
References
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