Idiopathic Midaortic Syndrome: An Unusual Case of Acute Kidney Injury (AKI) in Secondary Hypertension With Renal Collaterals in an Adult.

Midaortic syndrome (MAS) is a rare vascular disorder characterized by segmental narrowing of the distal thoracic or abdominal aorta, accounting for only 0.5-2% of aortic coarctations. Adult-onset idiopathic MAS is particularly uncommon and typically presents with refractory secondary hypertension, whereas dialysis-dependent acute kidney injury (AKI) is an exceptionally rare manifestation. A 44-year-old man with a history of smoking and alcohol use presented with oliguria, vomiting, left flank pain, severe hypertension (210/110 mmHg), and advanced renal failure (serum creatinine 8.0 mg/dL). Laboratory investigations revealed mild proteinuria, microscopic hematuria, and thrombocytopenia, while autoimmune, infectious, and thrombotic evaluations were unremarkable. Renal biopsy demonstrated moderate acute tubular injury with minimal chronic changes. Despite initiation of hemodialysis and intensive antihypertensive therapy, the patient remained dialysis dependent. Careful re-examination identified diminished lower-limb pulses and a significant upper- to lower-limb blood pressure gradient. CT aortography demonstrated complete occlusion of the abdominal aorta distal to the superior mesenteric artery with extensive bilateral renal collateral circulation, consistent with idiopathic MAS. PET imaging excluded active large-vessel vasculitis, and the absence of significant atherosclerotic disease supported an idiopathic etiology. A repeat renal biopsy again showed acute tubular injury without significant fibrosis or hypertensive vascular changes. Given the preserved collateral renal perfusion, dialysis frequency was gradually reduced and ultimately discontinued. Over the subsequent two weeks, urine output increased to 1.5 L/day, accompanied by progressive recovery of renal function and resolution of volume overload. This case highlights that idiopathic MAS should be considered in adults presenting with refractory hypertension and unexplained dialysis-dependent AKI, particularly when pulse deficits or inter-limb blood pressure discrepancies are present. Extensive collateral renal circulation may preserve renal viability despite complete aortic occlusion. Recognition of this unique hemodynamic physiology may prevent unnecessary prolonged dialysis, as excessive ultrafiltration may compromise collateral-dependent renal perfusion and delay renal recovery.