What is Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)?
Nutcracker syndrome, also known as left renal vein entrapment, is a condition where the left renal vein is squeezed, often between two large blood vessels, the aorta and the superior mesenteric artery. This squeezing leads to a build-up of blood in the left kidney and structures further down the vein. The symptoms of Nutcracker syndrome can vary and may include pain in the side of the body (flank), blood in the urine (hematuria), protein in the urine (proteinuria), a knot of swollen blood vessels in the scrotum (varicocele), varicose veins, painful menstrual periods (dysmenorrhea), and in less commonly, low blood pressure (hypotension) and quickened heart rate (tachycardia). Nutcracker syndrome can lead to serious health problems, such as long-term kidney disease and blood clots in the veins (venous thrombosis).
An anatomist named Grant first identified the compression of the left renal vein between the aorta and the superior mesenteric artery in 1937. In 1972, de Schepper gave it the name we use today. The term Nutcracker syndrome is used when a patient shows symptoms due to this abnormal compression, while the term Nutcracker phenomenon refers to this compression found on imaging but without any symptoms. The latter is considered a normal variant if found by chance on imaging.
Nutcracker syndrome can happen at any age but it usually peaks during a person’s 20s and 30s, which is the time when the spine’s bones have fully matured.
There are two main types of Nutcracker syndrome:
– The first and more common type is the anterior Nutcracker syndrome, where the left renal vein is squeezed between the aorta and the superior mesenteric artery.
– The second, less common type, is called posterior Nutcracker syndrome where the left renal vein is squeezed between the aorta and the spine.
The left renal vein can also be compressed by other conditions, such as cancer, swollen lymph nodes (lymphadenopathy), an exaggerated spinal curve (severe lordosis), abnormal intestinal positioning at birth (intestinal malrotation), pregnancy, and rapid weight loss.
What Causes Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)?
Nutcracker syndrome is a condition that occurs when the space between the aorta (the main and largest artery in the body) and the superior mesenteric artery (a large artery supplying blood to the intestines) narrows to less than 40°. This narrowing squeezes the left renal vein, a blood vessel that drains blood from the kidney. Normally, there is a 4 to 5 mm space between these vessels, maintained by fatty tissue and part of the intestine, the third section of the duodenum. People who are thinner are more likely to have symptoms of nutcracker syndrome, and gaining weight can sometimes relieve the condition.
Normally, the left renal vein passes in front of the aorta and drains into a large vein called the inferior vena cava. In people with nutcracker syndrome, the superior mesenteric artery’s starting point may be more to the side or lower than usual, which causes the angle to become too narrow.
The left renal vein results from an embryonic structure that usually degrades. Instead, if the wrong structure degrades or fails to do so, the left renal vein can be behind the aorta (retroaortic) or surrounding the aorta (circumaortic). This places the vein in a position where it can be squeezed between the aorta and the backbone.
Other unusual blood vessel formations have been linked to nutcracker syndrome, such as splitting and branching of the left renal vein. Less common causes of nutcracker syndrome include:
* Enlargement of the aorta (abdominal aortic aneurysm)
* Pressure from swollen lymph nodes or tumors near the renal vein
* Excessive inward curve of the lower spine (high-grade lordosis)
* Abnormal positioning of the intestines (intestinal malrotation)
* Pregnancy
* Significant weight loss in a short period
Another condition that has a similar cause is superior mesenteric artery syndrome. This condition is characterized by the duodenum (first part of the small intestine) being squeezed between the aorta and the superior mesenteric artery.
Risk Factors and Frequency for Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
The occurrence of nutcracker syndrome changes with age, but we don’t know exactly how common it is. This is mostly because nutcracker syndrome is often overlooked due to its non-specific symptoms, different ways it can appear clinically, and because there are no strict rules for diagnosis.
The age when people are diagnosed with nutcracker syndrome varies widely, starting from infancy up to the seventh decade of life. It tends to be especially common during two age ranges – the second to third decade of life and middle age. This might be explained by the fast growth of the spinal bones and increase in height during puberty, which might cause a narrowing of the space between aorta and superior mesenteric artery. This narrowing might be the reason why nutcracker syndrome occurs more frequently in these age groups.
- Nutcracker syndrome is equally common in men and women.
- However, men usually get diagnosed at a younger median age of 24 years, compared to women who get diagnosed at 29 years.
- Certain ethnic groups among children with nutcracker syndrome may be more prone to blood in their urine.
Nutcracker phenomenon might actually affect many people. According to some studies, over half of all people without symptoms have more than a 50% increase in the size of the left kidney vein on the side of the superior mesenteric artery. This is because the superior mesenteric artery compresses it, which is often seen as normal in people without symptoms.
Signs and Symptoms of Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
Nutcracker syndrome is a condition that can cause a variety of symptoms. The most common ones are unexplained, intermittent bleeding in urine, left-sided abdominal pain, and protein in the urine. Among patients, percentages of specific symptoms vary: 79% experience blood in urine, 38% experience left-side abdominal pain, 36% have enlarged veins in the scrotum (varicocele), 31% have protein in their urine, and 13% show signs of anemia. Women with this syndrome may additionally show signs related to enlarged veins in ovaries and uterus, including pelvic pain, pain during sexual intercourse, severe menstrual pain, and incontinence. If the pelvic veins are overcrowded, it could lead to chronic pelvic pain, particularly when standing. Patients described this type of pain as something they’ve experienced over a span of six months.
Those with nutcracker syndrome are often healthier individuals who are tall and slim. The physical examination might show abnormally large and twisted varicose veins in their lower body. Men may have varicoceles, or enlarged veins on the left side of their scrotum, which can be felt as lumps and cause testicular discomfort and a feeling of heaviness. These varicoceles are typically soft, obvious, can be compressed, and do not cause pain. They’re often described as a “bag of worms”. In women, the physical examination might reveal varices in the vulva or pelvis.
Testing for Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
Nutcracker syndrome is typically diagnosed by ruling out other medical conditions. Even though doctors may run lab tests, the results are not likely to provide a definite ‘yes’ or ‘no’ answer. If you have blood in your urine, your doctor will want to confirm this with a test and keep track of your hemoglobin levels. In cases where people have protein in their urine, a detailed investigation of the quantity of protein should be carried out.
A common first step in investigating this syndrome is a computed tomography (CT) scan. This can reveal the angle between the superior mesenteric artery and the aorta, and any present venous collaterals, if the radiologist is alert to these signs.
Some General Guidelines For Diagnosing Nutcracker Syndrome:
• Anyone suspected of having Nutcracker Syndrome should have a renal Doppler ultrasound. This includes young patients with unexplained instances of passing visible blood or blood cells in their urine, high levels of protein in their urine, and left flank pain. If the results can’t be clearly interpreted, it might be necessary to perform a CT or MRI.
• Scoping the bladder and ureters, although not absolutely necessary to diagnose Nutcracker Syndrome, might be helpful in ruling out other causes of blood in the urine.
• If you’re considering surgery, a contrast venogram, an x-ray of the veins with dye, might be useful to measure the size of vessels and possibly the pressure inside them.
Ultrasounds can be particularly useful, but require careful preparation and an expert operator to get accurate results. In children and pregnant people, who can’t be exposed to radiation, ultrasounds are the ideal way to investigate for Nutcracker Syndrome. Using an ultrasound machine, the doctor can measure the flow of blood and size of the vein, which can help in diagnosis.
CT scans are able to give detailed information about your kidney’s blood vessels without the need for any invasive procedures. However, these scans don’t provide information about the blood flow.
Magnetic Resonance Imaging (MRI) is another imaging technique that can provide detailed information about the anatomy of the blood vessels without exposing the patient to any radiation. This makes it an especially preferred choice for children and pregnant people.
In patients who may need surgery, contrast-enhanced venography (an x-ray of the veins with a dye) can provide direct information about blood flow and pressure in these veins. However, performing this test isn’t always necessary because it involves a minor surgical procedure.
A special type of ultrasound, known as intravascular ultrasound, can be performed at the same time as a venogram, to provide additional measurements. This can be particularly useful in cases where a stent (a tiny tube) might need to be inserted into the vein to relieve pressure.
Sometimes, a direct examination of the bladder and ureters might be necessary to rule out other causes of hematuria (blood in the urine). In patients with Nutcracker Syndrome, particularly those who are underweight, this procedure might reveal blood coming from the left ureter.
Treatment Options for Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
If you have nutcracker syndrome but do not experience any symptoms, you usually won’t need any treatment. The need for treatment depends on the symptoms you are experiencing. Possible treatments include non-surgical methods, placing a stent inside the blood vessel (endovascular stenting), and surgery.
For adult patients with mild symptoms, the European Society for Vascular Surgery suggests treating the condition without surgery for six months, and for two years in children aged 18 and under.
Conservative Treatment
Kids with nutcracker syndrome should be handled with as few medical treatments as possible. This is because symptoms often go away on their own as the child grows and bodies change. In fact, nearly 75% of pediatric patients diagnosed with nutcracker syndrome will experience complete resolution of their symptoms within two years of diagnosis.
For children who do have symptoms, doctors may suggest medicine known as angiotensin-converting enzyme (ACE) inhibitors. For patients with a specific condition known as orthostatic proteinuria, treatments like low-dose aspirin or ACE inhibitors can be beneficial. Patients may also use tight stockings to alleviate pelvic or lower back pain. Weight gain could help those who are underweight or have a normal weight but towards the lower end, to resolve the symptoms.
Surgical Treatment
If you’re an adult and you have severe pain and blood in your urine, your doctor might recommend surgery. Other reasons to consider surgery include issues with the nervous system, a high amount of protein in the urine, kidney failure, and varicocele, a condition where veins in the testicle become enlarged.
The surgeries that are typically performed include renal vein transposition, gonadal vein transposition, venous bypass, renal autotransplantation, and endovascular stenting. A nephrectomy, the removal of a kidney, is usually considered a last resort when other options can’t relieve the pressure in the veins.
There are some potential complications to these procedures including deep vein thrombosis (a blood clot), a buildup of gas in the stomach following surgery, and the buildup of blood in the cavity lining in the abdomen. Sometimes additional treatment might be required after the surgery.
For those with gonadal venous reflux, a condition where blood flows backwards into the veins, the gonadal vein transposition can help relieve pressure on the kidney.
If pressure needs to be reduced in the left renal vein, renal autotransplantation may be necessary. This involves moving the kidney to the opposite side of the body. However, this procedure can take a long time and involve more complicated surgery. There are methods for performing this procedure using laparoscopic or robotic techniques, but these can still take longer and may be more expensive.
Stenting is a procedure where a device is inserted into the renal vein to stop it from narrowing. This procedure was first introduced in 1996, and the results have been favorable. In some cases, this procedure can be combined with a balloon angioplasty if left renal vein narrowing continues after the stent is installed. Stent migration (moving out of place), causing damage to nearby structures, and bending are the most common complications of these procedures. However, a hybrid procedure can be used to suture the stent to the vein wall to reduce risk.
After these procedures, a 3 month course of anticoagulation (blood-thinning) therapy is recommended to help the stent become part of the vein wall. Patients are usually checked using ultrasound after 3 months and then once a year for 3 years, then every 3 to 5 years after that.
What else can Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment) be?
The main symptoms of Nutcracker Syndrome, which are blood in the urine (hematuria) and pain in the side of the body between the ribs and the hip (flank pain), can also be signs of other health problems. These can include cancer, kidney disease, pelvic congestion not related to Nutcracker Syndrome, kidney infections, and kidney stones. Nutcracker Syndrome can sometimes occur at the same time as other conditions like May-Thurner Syndrome, pregnancy, or IgA kidney disease, which can make it even more difficult to figure out the correct diagnosis.
Along with Nutcracker Syndrome, other conditions such as tumors in the space behind the lower abdominal organs (retroperitoneal tumors), a tear in the aorta (aortic dissection), swollen lymph nodes (lymphadenopathy), and Loin Pain Hematuria syndrome can cause compression of the left renal vein (the blood vessel carrying blood from the left kidney back to the heart).
The symptom of blood in the urine could be indicative of many other health problems not limited to injury, infection or cancer. Certain kidney conditions such as Thin Basement Membrane Disease (formerly known as Benign Familial Hematuria) and Benign Essential Hematuria can also cause blood to appear in the urine even without other symptoms.
What to expect with Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
Nutcracker syndrome gets better in about 75% of young patients who have it. Factors like gaining weight, growing, and the development of new pathways for blood flow (venous collaterals) can help with this improvement. However, if symptoms still persist, nutcracker syndrome could cause a blood clot in the left kidney vein and kidney injury.
There have been cases where patients with this condition have experienced blood in their urine severe enough to need a blood transfusion, which carries additional risks.
Possible Complications When Diagnosed with Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
If nutcracker syndrome is left untreated, it can gradually lead to kidney problems. In some cases, it can cause an unusual bulge, called a saccular aneurysm, to form in the left kidney vein. These aneurysms can rupture or cause blood clots, which can then disrupt the blood flow in the veins and lungs.
The poor blood flow from the left testicular or ovarian vein can result in complications. In men, it can lead to swollen veins in the scrotum (varicoceles), and in women, it can lead to pelvic congestion syndrome. Both conditions can cause infertility.
Additional reported complications include significant blood in urine and abnormal protein loss in the urine when standing. Moreover, patients with both nutcracker and May-Thurner syndromes may experience worsening of symptoms if only one syndrome is treated.
Related surgeries can bring about complications such as bleeding in the abdomen (retroperitoneal hematoma), delayed digestion (ileus), and blood clots in the deep veins. The veins can narrow again over time (restenosis), and the use of implants such as stents can lead to their displacement and migration to the vena cava, heart, or lungs.
In a 2016 study of 75 patients, stent migration was observed in five patients over a rough average of 55 months of monitoring. The researchers found that careful measurement of the left kidney vein, stent choice, stent placement, and early detection of complications helped to reduce such occurrences.
Main Potential Complications:
- Progressive kidney dysfunction
- Saccular aneurysm in the left kidney vein
- Varicoceles in men and pelvic congestion syndrome in women
- Infertility
- Blood in urine and abnormal protein loss in the urine when standing
- Complications from concurrent nutcracker and May-Thurner syndromes
- Retroperitoneal hematoma, ileus, and deep vein thrombosis from surgeries
- Vein narrowing (restenosis)
- Stent displacement and migration
Recovery from Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
Doctors suggest that patients undergoing treatment for nutcracker syndrome should be on blood-thinning therapy for three months. Those patients with a greater chance of forming blood clots might need to continue this therapy for a longer, possibly unlimited time. After treatment, patients should be checked again after a span of three months, and then once a year thereafter.
If the patient has no symptoms, their check-up schedules may be spaced out to every 3 to 5 years. However, if the symptoms return, patients should undergo computed tomography angiography (CTA) or direct contrast venography. These are imaging processes that help doctors visualize the veins in the body and understand any issues better.
Preventing Nutcracker Syndrome and Left Renal Vein Entrapment (Left Renal Vein Entrapment)
Patients should be informed about the potential problems that can occur if nutcracker syndrome is left untreated. This includes a conversation about the possible risk of not being able to have children for those who have pelvic congestion syndrome or varicoceles – enlarged veins in the scrotum. Family members don’t need to be screened because nutcracker syndrome cannot be passed down through families.
