1 Department of Renal Medicine and Transplantation, Guy's Hospital, London, 2 Department of Surgery, Guy's and St Thomas' NHS Trust, London, 3 Department of Nuclear Medicine, Guy's Hospital, London
Keywords: mid-aortic syndrome; renal ischaemia; collateral circulation; spontaneous reperfusion
Introduction
Mid-Aortic Syndrome is a rare condition affecting children and young adults. The term is a clinico-pathological definition referring to isolated disease of the abdominal aorta comprising significant proximal tubular narrowing with stenosis of the renal and visceral branches (1). The natural history of untreated symptomatic Mid-Aortic Syndrome is invariably death before the fourth decade (1). Uncontrollable hypertension and deteriorating renal function are the main indications for surgical intervention.
We report a case of acute renal failure in a patient with Mid-Aortic Syndrome following the development of renal artery thrombosis in the setting of reconstructive surgery. Unusually, following sixty days of anuria, spontaneous reperfusion of the thrombosed vessels occurred with recovery of dialysis independent renal function. This case illustrates the capacity of the kidney to adapt to prolonged ischaemia with maintenance of tissue viability and ultimate recovery of renal function.
Case
An 18-year-old woman presented with a 3-year history of progressive intermittent claudication. At presentation all lower limb pulses were weak. She was hypertensive (150/80 mmHg) and renal artery bruits were audible bilaterally.
Angiographic studies demonstrated a long tubular stenosis of the descending thoracic aorta with a further tight stenosis below the level of the coeliac axis (Figure 1). Duplex renal arteries were present bilaterally with ostial stenosis of all four vessels. The angiographic findings depicted mid aortic syndrome with unusual involvement of the descending thoracic aorta.
|
|
Over the following 24 hours the patient remained hypertensive (195/100 mmHg) and oliguria ensued with serum creatinine increasing to l88 µmol/l. Renal perfusion was absent on Doppler sonography. Emergency surgical intervention followed, demonstrating thrombosis of the proximal graft with occlusion of all four renal arteries. Thrombectomy of each occluded renal vessel was performed, successfully re-establishing blood flow.
Despite surgical intervention the patient remained oliguric and hypertensive with a rapidly rising serum creatinine (290 µmol/l). Angiography performed 24 hours later confirmed patency of the coeliac axis but revealed all renal arteries other than that supplying the lower pole of the left kidney had occluded. Prognosis for recovery of renal function was considered poor.
In the presence of worsening acidosis, persistent oliguria, and deranged liver function tests bicarbonate buffered continuous veno-veno haemo-diafiltration (CVVHDF) was commenced.
Adult respiratory distress syndrome followed an episode of aspiration, which necessitated a 6-week period of mechanical ventilation. The patient's clinical course was further complicated by patchy infarction of the right hepatic lobe and gastrointestinal bleeding secondary to severe erosive gastro duodenitis.
Following 60 days of CVVHDF, a small urine output was re established. This rapidly increased to 100 ml/hour under the influence of intravenous frusemide. Haemodiafiltration was ceased and the creatinine fell to 110 µmol/l at the time of discharge 78 days after the original surgical procedure.
Ten weeks following surgical intervention, renal 99Tc DMSA scan demonstrated loss of function consistent with infarction at the upper pole of the left kidney and the lower pole of the right kidney. Split function glomerular filtration rate was 12.9 ml/min for the right kidney and 12 ml/min for the left.
Doppler sonography performed one month after discharge showed a widely patent graft with flow detected in a single renal artery on the left and a single artery on the right, the remaining arteries apparently occluded.
6 months later magnetic resonance angiography demonstrated perfusion of a single renal artery on the right and two on the left. Significant scarring of both kidneys was also noted. Serum creatinine was 86 µmol/l with an associated increase in glomerular filtration rate to 35.9 ml/min. This remarkable recovery persists despite the need for high dose beta-blocker and calcium channel antagonist treatment for blood pressure control.
Discussion
In recent years there has been increasing appreciation of the importance of ischaemic renal disease as a significant cause of end stage renal failure. There have been a number of reports of successful outcome following delayed revascularization in patients with renal atherosclerosis (2), fibromuscular dysplasia (3) and Takayasu's arteritis (4). This case demonstrates remarkable capacity for recovery of renal function following prolonged ischaemia.
The potential for renal recovery following ischaemic injury is dependant on a number of variables including duration of hypoperfusion, the acuteness of the arterial occlusion, comorbidity and inherent ability of the kidney to augment structural and functional protective responses.
Ischaemic renal disease is characterised by a fall in glomerular filtration rate due to reduction in renal perfusion pressure below autoregulatory limits (<80 mmHg) which corresponds to a 70% reduction in arterial diameter (5).
Chronic underperfusion as in this case provides a window for adaptive responses which may protect renal tissue from acute infarction following complete occlusion of a renal artery. These adaptive responses preserve oxygen delivery, reduce oxygen demand and interfere at a cellular level with damage mechanisms resulting from oxygen deficit.
The most obvious structural adaptation is the development of collateral circulation allowing maintenance of parenchymal viability despite critical reduction in renal perfusion. Animal models have demonstrated that collateral circulation may be induced by gradual reduction of renal arterial luminal area (6). It has been shown with angiographic studies that 40% of patients with renal artery stenosis greater than 35% will develop renal artery collaterals (7). The collateral arterial supply derives from adrenal, lumbar, gonadal and peri-ureteric arteries. The development of a collateral network between the segmental and interlobular arteries is associated with improved maintenance of renal size and function. The establishment of a renal collateral circulation is positively influenced by a number of factors including the location and number of occluding arterial lesions, the rate of progression of obstruction, the availability of extra renal collateral arterial sources and the status of the aorta (7). In addition, the condition of the underlying kidney which will be significantly affected by the age of the patient is important in determining both the degree to which collateral circulation develops and the effectiveness of the newly established circulation in the preservation of renal function (7). As illustrated in this case, young age and the absence of co-morbidity provide the best circumstances for recovery of function following prolonged renal ischaemia.
The kidney at risk of chronic ischaemic injury also modifies its function to reduce its oxygen demand. This is achieved by limiting solute delivery to the tubule and decreasing epithelial transport activity. In the long term the chronically ischaemic kidney undergoes atrophy which involves loss of and reduction in size of tubular epithelial cells. This is a protective response to ischaemia and is reversible upon reperfusion of the kidney (8).
Although this case illustrates partial recovery of renal function following prolonged ischaemia, patchy infarction and significant residual scarring of both kidneys remained. The pattern of injury and the capacity of renal tubular cells to regenerate may be dictated by the mode of cell death (necrosis vs apoptosis) and whether the tubular basement membrane remains intact (9).
The clinical context is of importance in predicting the outcome of renal reperfusion. The patient in this case was young with no antecedent comorbidity, the ischaemic injury purely reflecting renal hypoperfusion. This contrasts with the more usual clinical situation of atheromatous renal artery disease in an elderly population, the outcome of revascularization being influenced by comorbidity in the form of diabetes mellitus, dyslipidaemia and essential hypertension.
Most case reports describing recovery of dialysis independent renal function following prolonged arterial occlusion involve a surgical revascularisation procedure. This case was unusual in that the occlusion occurred following the surgical revascularization with reperfusion of the kidneys being achieved by spontaneous autolysis of the thrombosed vessels.
In summary this case illustrates that even following prolonged renal ischaemia there are situations where recovery may be anticipated. This may be favourably influenced by a preceding period of subcritical hypoperfusion providing a window for the development of protective adaptive responses, young age and the lack of other co-morbid factors.
Notes
Correspondence and offprint requests to: Dr Rosemary Masterson, Department of Renal Medicine, Guy's Hospital, St Thomas' Street, London SE1 9RT, UK.
References