Nutcracker syndrome (NS) is a condition in which two arteries compress the left renal vein (LRV), interfering with blood flow out of the left kidney. The condition has this name because the compression resembles a nutcracker cracking a nut.

NS does not always cause symptoms, but some people may experience left flank pain and blood and protein in the urine. Some cases of NS resolve on their own, while others may lead to complications such as kidney damage, anemia, and infertility.

This article describes NS, including its symptoms, causes, diagnosis, and treatment.

A walnut being crushed in a nutcracker, which nutcracker syndrome is named after.Share on Pinterest
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The kidneys are two bean-shaped organs located on either side of the lower spine. They are responsible for removing waste from the blood. Each kidney has a renal vein that carries filtered blood into the circulatory system.

The LRV carries blood from the left kidney to a large vein called the inferior vena cava (IVC). The IVC receives deoxygenated blood from the lower body and delivers it to the heart.

Before reaching the IVC, the LRV passes between two major abdominal arteries: the abdominal aorta and the superior mesenteric artery. In NS, there is not enough space for the LRV to pass between these two arteries. Instead, the arteries press on and compress the LRV, interfering with blood flow.

When NS occurs, blood can flow backward into other veins, causing an increase in pressure. This can lead to symptoms such as left flank pain and blood and protein in the urine.

There are two main types of NS: anterior and posterior. Anterior NS is more common and involves compression of the LRV between the abdominal aorta and another artery. Posterior NS is less common and involves compression of the LRV between the abdominal aorta and the spine. Some experts also recognize a mixed type, which involves various changes to the blood vessels.

NS is not life threatening. However, without treatment, the condition can cause serious complications, including long-term kidney damage.

The symptoms of NS can vary depending on the extent of LRV compression. Some people do not experience any symptoms.

When symptoms occur, they may include:

NS occurs as a result of compression of the LRV.

The following conditions can lead to LRV compression:

  • anatomic irregularities, such as a small pelvis or an unusually shaped aorta
  • injury
  • tumors
  • an aneurysm in the abdominal aorta
  • pregnancy

NS can affect people of any age or sex but is more common among females in their 30s and 40s.

Children may develop NS after rapid growth during puberty. However, NS in children typically causes only mild symptoms and often resolves without treatment.

When diagnosing NS, a doctor will ask about a person’s symptoms and medical history and perform a physical examination.

The doctor will then order urine tests to look for blood and protein in the urine, as well as blood tests to check blood cell counts and kidney function.

They may also order one of the following imaging tests to assess blood flow and look for any vascular blockages or abnormalities:

If a person experiences mild symptoms of NS, their doctor may recommend simply observing the symptoms to see whether they resolve on their own.

If symptoms do not improve after 6 months, the doctor may recommend medications such as low dose aspirin and angiotensin-converting enzyme (ACE) inhibitors. If symptoms persist, surgery may be necessary to relieve pressure on the LRV.

Surgical options for NS include:

  • Venous stenting: This involves inserting a small tube, or stent, into the LRV to keep it open.
  • Blood vessel surgery: This involves rerouting the blood vessels using vein grafts or by moving the compressed vessels.
  • Nephrectomy: This involves removing the affected kidney. It is an extreme option that is only appropriate when other treatment options have failed and evidence of kidney damage is present.

Most people who undergo surgery will need several weeks to recover. Individual recovery times depend on the severity of the condition and the type of surgery a person has.

People who undergo venous stenting typically recover much more quickly than those who undergo more complex procedures such as nephrectomy.

After surgery, doctors use a test called estimated glomerular filtration rate (eGFR) to monitor kidney function. People who undergo nephrectomy may find that their eGFR takes months to years to recover.

A person who has had surgery may need to take blood thinners or undergo additional surgeries.

NS can resolve spontaneously in some cases, particularly in children.

However, untreated NS can lead to the following complications:

A person may also experience complications after having surgery for NS, such as:

  • blocked blood flow due to stent migration or dislodgement
  • blood clots
  • infection
  • kidney damage

After surgery, a person will have regular follow-ups with their doctor. They may have blood, urine, and imaging tests every few months to check for any blockages or irregularities in the veins. People who have had a nephrectomy may require lifelong eGFR tests to monitor the functioning of their remaining kidney.

A person should consult their doctor if they experience any of the following symptoms after surgery for NS:

Nutcracker syndrome (NS) is a condition in which the left renal vein becomes compressed. This can restrict blood flow, which may lead to symptoms such as left flank pain and blood and protein in the urine.

NS sometimes resolves on its own, especially in children. However, persistent symptomatic NS can cause kidney damage and other complications, such as blood clots, anemia, and infertility.

Doctors typically diagnose NS using a combination of urine tests, blood tests, and imaging tests.

Treatment options include observation, medications, and surgery. Doctors typically recommend surgery only when other treatment options have failed and evidence of kidney damage is present.