What Is Nutcracker Syndrome?

Overview

Nutcracker syndrome is a rare condition that occurs when the left renal vein (which carries the blood away from the left kidney back to the heart) is compressed between the abdominal aorta and the superior mesenteric artery. This compression causes narrowing or obstruction of the left renal vein, leading to impaired blood flow from the left kidney to the inferior vena cava. As a result, the nearby veins can become swollen and implicate potential complications.

The name "nutcracker" refers to the compression of the renal vein between the two arteries, which resembles the action of a nutcracker crushing a nut. That said, the condition can lead to a variety of symptoms, including flank pain, abdominal pain, blood in the urine, varicocele in males (swelling of veins in the scrotum), and pelvic congestion syndrome.

Kidneys are the two bean-shaped organs present on either side of the spine, just below the rib cage. They are responsible for several essential functions in the body, including removing waste and excess fluids from the blood, regulating blood pressure, balancing electrolytes, producing hormones, activating vitamin D for healthy bone function, and much more.

Each of our kidneys typically contains one vein that takes filtered blood from the kidneys to the circulatory system. These are known as renal veins. Usually, each of them is present on the right side and on the left side. Although variations in them are possible.

Anatomically, your left renal vein leaves the left side of the kidney and passes through the inferior vena cava. The inferior vena cava is a particularly large vein that is responsible for collecting oxygen-poor blood from the other veins present in the lower body and then taking it back to the heart.

To reach the inferior vena cava, the left renal vein is supposed to travel through two major arteries in your abdomen known as the abdominal aorta and the superior mesenteric artery. Generally, there is enough space for the vein to travel through these two arteries.

However, in the case of nutcracker syndrome, the space between the abdominal aorta and the superior mesenteric artery is not sufficient.These major arteries can squeeze the left renal vein. This is referred to as anterior nutcracker syndrome, which is the most common condition, and compression generally occurs in front of the aorta.

In some cases, the compression may also happen behind the aorta, called the posterior nutcracker syndrome. Many researchers have also determined other variations of this condition, but they are mostly rare. In some instances, nutcracker syndrome is also known as left renal vein entrapment.¹

Causes of nutcracker syndrome

The exact cause of nutcracker syndrome is still debatable. Though, according to many researchers, the "nutcracker phenomenon'' occurs when there are changes in the blood vessel anatomy. These changes may happen in the womb when your blood vessels are forming, or they may occur due to growth spurts, especially in teenagers, or when someone loses lots of weight, as a change in body proportions can cause renal vein compression. Moreover, it is known that children are likely to experience fewer symptoms of the nutcracker syndrome in comparison to adults.

Signs and symptoms of nutcracker syndrome

The symptoms of nutcracker syndrome that individuals may observe include:

• Hematuria - blood in the urine
• Flank pain on the left side
• Headaches
• Feeling fatigued

Nutcracker's symptoms may also vary based on gender. For instance, people assigned male at birth (AMAB) can experience varicocele, which is an enlargement of the veins in their scrotum.

Females may experience any of the following nutcracker symptoms, such as:

• Pain during urination (dysuria)
• Pain during intercourse (dyspareunia)
• Feeling pain in the pelvic region

Healthcare providers may conduct diagnostic testing to evaluate some clinical signs of the nutcracker syndrome. This may include:

• Examining signs of anaemia (low red blood cell levels)
• The presence of microscopic amounts of blood in the urine, known as microhematuria
• Checking the levels of protein in the urine (proteinuria)

Management and treatment of nutcracker syndrome

Generally, treatment options for nutcracker syndrome greatly depend on the individual's age and the severity of the symptoms. In most cases, if the symptoms are mild, doctors will likely suggest observation. They may even begin exploring management options with a conservative approach. A study showed that around 75% of the time, symptoms resolve on their own, especially among children under the age of 18.¹

However, if the symptoms of the nutcracker persist or get worse, your health provider might recommend surgery.

Conservative approach

Conservative management is considered an appropriate approach for many people, especially for children who are under 18 years of age. If a child has nutcracker syndrome, the doctors may advise following a conservative approach for at least 2 years. This may involve paying attention to the situation and assisting the child to gain more weight. Gaining weight can help to expand the belly region, which in turn alleviates pressure on the renal vein. For people over 18 years, the health providers usually recommend following a conservative approach for about six months. Moreover, conservative management may also involve medications to aid in restoring kidney function; these may include:

• ACE inhibitors.
• Aspirin.

Surgical treatment

If the symptoms of nutcracker syndrome become severe, then it is possible that a conservative approach may not help. In such cases, doctors may recommend surgical treatments consisting of minimally invasive procedures. The major goal of the surgical intervention is to give an open, convenient pathway for blood to stream through the kidney toward the heart. Some surgical procedures for treating nutcracker's syndrome include:

Renal vein transposition

This type of surgery involves moving the renal vein from its normal position in the body and attaching it to a different location. During the renal vein transposition procedure, the doctors may make an incision in the abdomen region to access the renal vein, which is then carefully dissected and freed from the nearby tissues. The surgeon will identify a new location for the vein and create a new pathway for the vein so it can travel to that location. This may also involve rerouting the vein around other structures in the body.

After carefully establishing the new pathway, the surgeon will connect the renal vein to the new location, generally either the vena cava or the external iliac vein. Once the incision is closed, the patient is monitored for several days to rule out any further complications. In some cases, laparoscopic methods are also used as an alternative treatment option to open surgery.

Renal vein transposition is usually considered a safe and effective procedure for managing nutcracker syndrome. However, similar to any surgical procedure, there may be risks involved, like bleeding, infection, and damage to the surrounding tissues.

Stent

Stent insertion is another minimally invasive method to treat nutcracker syndrome. This involves using a small stent that is inserted into the left renal vein to make a space in the vein so the blood can easily flow through it.

Renal autotransplantation surgery

In this type of surgery, doctors remove the kidney and re-implant it in a different location, usually near your hip bone.

FAQs

How is nutcracker syndrome diagnosed?

During the diagnosis of nutcracker syndrome, healthcare providers may take some time to evaluate the condition to rule out any other possible complications. They may perform an initial physical examination and go through your medical history before recommending diagnostic tests to evaluate you further. 

The testing for diagnostic studies of nutcracker syndrome may consist of the following:

• Blood test
• Urinalysis
• Doppler ultrasound.
• Computed tomography (CT scan)
• Magnetic resonance imaging, or MRI
• Intravascular ultrasound (IVUS)
• Venogram

Can nutcracker syndrome be prevented?

There's no known way to prevent nutcracker syndrome, as its occurrence is unpredictable. Though nutcracker syndrome is not inherited, it usually resolves on its own (especially in children) or with medical intervention.

Who is at risk of nutcracker syndrome?

Nutcracker syndrome is a rare health condition that can affect both adults and children. Although the specifics of prevalence are still debatable and can affect anyone, it is most likely observed in females ages 30–40 who are usually tall and slim. Moreover, there are some other conditions that may increase the risks of developing nutcracker syndrome in individuals. This may include:

• Low body mass index (BMI)
• Enlarged lymph nodes in the abdomen
• Pancreatic tumors
• Observing tumors in the tissue lining of the abdominal wall
• A serious lower spinal curve
• An abnormal swelling (aneurysm) in the abdominal aorta
• Sudden changes in weight or height
• Nephroptosis -  a condition where the kidneys can drop into the pelvic region when a person stands up
• Pregnancy

How common is nutcracker syndrome?

Many researchers consider nutcracker syndrome a rare condition. Though the exact prevalence of nutcracker syndrome is still not fully understood, it is believed that its occurrence rate may vary among various age groups.

According to a study, the prevalence may likely reach its peak in the middle-aged group or develop in the first 10–29 years of age, due to vertebral body progression during the times of puberty, where the narrowing of the aorta and superior mesenteric artery is possible.²

When should I see a doctor?

It is advised to make an appointment with your health provider if you experience symptoms of nutcracker syndrome or if your condition worsens.

In the case of having surgery, it is best to follow your doctor's given instructions, take postoperative care, and keep your scheduled appointments in check to avoid any health complications.

Summary

Nutcracker syndrome or phenomenon is a rare condition that happens when the left renal vein is compressed between the abdominal aorta and the superior mesenteric artery, leading to the obstruction of the vein. The compression of the left renal vein causes impaired blood flow from the left kidney to the inferior vena cava.

Nutcracker syndrome can affect anyone of any age, but it is particularly more frequent among females in their third and fourth decades. The nutcracker syndrome may cause a range of symptoms like flank pain, abdominal pain, hematuria, proteinuria, varicocele, and pelvic complications.

The main cause of nutcracker syndrome is still not fully understood. However, with proper diagnosis and imaging tests followed by the right treatment options, such as conservative management consisting of pain control, and close monitoring, as well as surgical management for severe cases, it is possible to relieve the compression of the left renal vein and follow a healthy lifestyle.