Renal artery stenosis is a condition characterized by the narrowing of one or both renal arteries, the blood vessels supplying blood to the kidneys. This narrowing can significantly reduce blood flow, potentially impairing kidney function. Understanding its underlying causes is important for addressing the condition.
Atherosclerosis: The Leading Cause
Atherosclerosis is the most frequent cause of renal artery stenosis, accounting for approximately 90% of cases, particularly in older adults. This systemic disease involves plaque buildup within arterial walls. Plaque consists of fats, cholesterol, immune cells, and other circulating substances.
When atherosclerosis affects the renal arteries, these plaques accumulate, leading to gradual narrowing and stiffening of the vessel. This restricts blood flow to the kidney. The diminished blood flow can activate hormonal systems, such as the renin-angiotensin-aldosterone system, which attempts to raise blood pressure to compensate for the perceived low blood volume to the kidney.
Several factors increase the likelihood of developing atherosclerosis, thus contributing to renal artery stenosis. High blood pressure, elevated cholesterol levels (especially LDL cholesterol), and diabetes are significant risk factors. Smoking also severely damages artery walls, accelerating plaque formation.
Age is another non-modifiable risk factor, with plaque buildup worsening over time; men generally see an increased risk after age 45 and women after age 55. Obesity, a sedentary lifestyle, and a family history of early cardiovascular disease further contribute to atherosclerosis risk. These factors collectively promote arterial damage that can manifest as renal artery stenosis.
Fibromuscular Dysplasia
Fibromuscular dysplasia (FMD) is the second most common cause of renal artery stenosis, distinct from atherosclerosis. This condition involves abnormal cell growth within artery walls, leading to narrowing or bulging. Unlike atherosclerosis, FMD is not caused by plaque buildup or inflammation.
The abnormal cell growth in FMD can create a characteristic “string-of-beads” appearance in imaging studies, where narrowed segments alternate with wider, dilated areas. This structural irregularity impedes normal blood flow to the kidneys. FMD commonly affects medium-sized arteries throughout the body, though the renal arteries are frequently involved.
FMD is more common in younger individuals, particularly women aged 30 to 50 years. While the exact cause of FMD remains unclear, smoking and genetic factors are proposed as potential contributors. The condition can lead to high blood pressure, and in some cases, may involve other arteries such as those supplying the brain, potentially causing headaches or stroke.
Other Conditions Contributing to Narrowing
Beyond atherosclerosis and fibromuscular dysplasia, several less common conditions can contribute to renal artery narrowing. Vasculitis, the inflammation of blood vessels, is one such cause. Specific types, like polyarteritis nodosa and Takayasu’s arteritis, can directly affect the renal arteries, leading to stenosis or even occlusion. This inflammation can disrupt blood flow and potentially damage kidney tissue.
Neurofibromatosis Type 1 (NF1), a genetic disorder, is another condition that can cause renal artery stenosis. In individuals with NF1, abnormal cell growth affects arterial walls, leading to narrowing, most commonly at the origin of the renal artery. NF1 is a notable cause of hypertension in children and young adults.
Previous radiation therapy to the abdominal area can also induce renal artery narrowing. Radiation can accelerate atherosclerosis development within the irradiated field, leading to stenosis many years after treatment. This is a recognized complication, though it is relatively rare.
Rarely, a dissection or aneurysm of the aorta, the body’s main artery, can extend into or compress the renal arteries. An aortic dissection involves a tear in the inner layer of the aorta, allowing blood to flow between the layers and potentially obstruct the openings of other arteries, including the renal arteries.
Finally, external compression of the renal artery by surrounding structures, though very rare, can also lead to stenosis. This might occur due to unusual anatomical bands, tumors, or other masses that physically press on the artery.