Renal artery stenosis

What it is

Renal artery stenosis is narrowing of the renal arteries causing reduced renal perfusion and RAAS activation. That makes it one of the renal causes of secondary hypertension, and the same fall in perfusion also places it among the causes of prerenal acute kidney injury.

Causes and risk

Renal artery stenosis is the most common cause of secondary hypertension in adults 65 years of age and older, while under 40 years of age the most common causes are thyroid dysfunction, fibromuscular dysplasia and renal parenchymal disease. Fibromuscular dysplasia is 90% women in adults.

It heads the short list of causes of secondary hypertension that is worth keeping whole: renal artery stenosis, renal failure, hyperthyroidism, pheochromocytoma, hyperaldosteronism, Cushing syndrome and obstructive sleep apnoea. The two indications to evaluate for secondary hypertension at all are age under 40 and resistant hypertension.

How it presents

• New-onset or worsening hypertension, a bruit over the renal artery, and asymmetric kidney size.
• Signs that should raise the question of secondary hypertension in general are severe hypertension, resistant hypertension, target organ damage disproportionate to the degree of hypertension, hypertensive emergency, abrupt onset, onset at less than 30 years of age, onset of diastolic hypertension at more than 65 years of age, exacerbation of previously controlled hypertension, drug-induced hypertension, and unprovoked or significant hypokalemia.
• Renovascular hypertension from renal artery stenosis is one of the differential diagnoses of hypertension with hypokalemia, alongside primary hyperaldosteronism, renin secreting tumors, CAH and Cushing's.
• In fibromuscular dysplasia, renal artery stenosis gives secondary hypertension and flank pain, and examination may find a subauricular systolic bruit and an abdominal bruit.

In the table of secondary hypertension the clues that name renovascular disease are four: severe hypertension, 180 mm Hg systolic or more and/or 120 mm Hg diastolic, after age 55; possible recurrent flash pulmonary edema or resistant heart failure; an unexplained rise in serum creatinine; and an abdominal bruit. Those four are what separate it from the others in the same table, since renal parenchymal disease shows an elevated serum creatinine with an abnormal urinalysis, proteinuria and red blood cell casts; primary aldosteronism shows easily provoked hypokalemia with slight hypernatremia; and pheochromocytoma shows paroxysmal elevated blood pressure with tachycardia, pounding headaches, palpitations and diaphoresis. So an older patient with resistant hypertension, an abdominal bruit and a creatinine that rose for no clear reason is renovascular disease.

It is as useful to know where renal artery stenosis is offered and is not the answer. In a 12 year old boy with episodic headache at the back of the head, flushing, sweaty palms, hyperpigmented macules on chest and back, a heart rate of 104 beats/min and a blood pressure of 146/92 mmHg, with no bruits heard on abdominal examination, the diagnosis is pheochromocytoma and catecholamine production, not renal artery stenosis. In a 30 year old woman on no medications with intense fatigue, a blood pressure of 155/95 mm Hg, a sodium of 146 mmol/L and a potassium of 2.3 mmol/L, the answer is primary aldosteronism and not bilateral renal artery stenosis. And in a 24 year old man with lethargy and intermittent muscle spasms since childhood, a normal examination, a blood pressure of 132/76, a potassium of 2.4 mmol/L and an Mg of 0.32 mmol/L, the answer is Gitelman's syndrome, since the blood pressure is not raised at all.