Renovascular Hypertension Causes and Diagnosis

Renovascular hypertension is a type of secondary hypertension caused by abnormal changes in the regular blood flow to the kidneys. While renovascular hypertension is sometimes discovered right away in patients who are known to have kidney problems, it is more commonly diagnosed after a period of observation and testing. Because of how the kidneys work, renovascular hypertension usually gets worse if it isn't treated.

Causes 

Medium-sized arteries called the renal arteries supply the kidneys with a constant flow of blood that must be filtered and returned to the body’s normal circulation. Because the filtering functions of the kidney are mainly powered by the force of the blood pressure, the kidneys are very good at sensing changes in blood pressure. If the kidneys sense that blood pressure is dropping too low to power normal blood filtration, they respond by releasing hormones that act to raise blood pressure.

If the flow of blood through the renal arteries decreases for any reason, the kidneys can be tricked into thinking that blood pressure is too low. For example, a disease called renal artery stenosis can cause the renal arteries to narrow, which decreases the amount of blood that flows into the kidneys. The kidneys detect this decrease and release the hormone renin in an attempt to raise blood pressure and restore normal blood flow.

Problems arise when, as in renal artery stenosis, the decrease in blood flow is not actually caused by low blood pressure. In these cases, the kidneys end up raising blood pressure to very high levels in order to push more blood through the narrowed renal arteries.

Diagnosis

In patients who are known to have blood vessel or kidney problems, suddenly developing high blood pressure is a strong signal that renovascular hypertension might be to blame. Usually, though, the diagnosis requires careful investigation and several tests. Some signs that suggest renovascular hypertension are:

• Very high blood pressure in people younger than 30
• Sudden onset of very high blood pressure in people older than 55
• Blood pressure that does not respond to drug treatment
• Blood pressure that stops responding to previously effective treatments

Blood tests are usually done in suspected cases of renovascular hypertension, but the only sure way to diagnose the problem is to actually see a narrowing of the renal arteries. This is usually done with a non-invasive procedure such as an MRI or CT scan, but sometimes more invasive measures are required. In these cases, a small catheter is threaded through the groin into the renal artery itself, and small amounts of dye are released from the catheter tip. Pictures are taken that show the course the dye follows; this will reveal any narrow spots in the artery.

Treatment

Treating renovascular hypertension is not the same as treating traditional high blood pressure. Because one of the hallmarks of the disease is its failure to respond to traditional drug treatments, the usual treatment methods are not effective. The high blood pressure component of renovascular hypertension is actually a symptom of the underlying disease — a narrowed renal artery — which must ultimately be treated.

Treatment options vary depending on what is causing the renal artery to narrow, but the goals are the same in each case — to widen the artery itself and restore normal blood flow to the kidney. The actual way this is accomplished depends on exactly what is causing the artery to narrow in the first place. In older people, the narrowing is usually the result of fatty deposits similar to those that can cause heart attacks. The first step in treatment is usually to try medicines that dissolve these deposits. If this is unsuccessful, more invasive options might be required, including physically expanding the vessel back to its normal size with a type of surgical procedure called stenting.

In some cases, the narrowing is due to conditions that are more difficult to manage. Certain diseases can make the walls of the blood vessels thicken, which can cause the vessel to narrow. This cannot be treated with medicine, so stenting — or even more invasive types of surgery — is usually needed. The exact treatment options in these cases depend on many factors that can vary from patient to patient, so definitive treatment plans are usually fairly patient specific.

Treating renovascular hypertension is more difficult than treating other, more "normal" types of high blood pressure, and though the success rate is high, it carries more risks and potential complications. Working with a doctor to develop an appropriate treatment plan is an important step to combating this serious disease.