Nutcracker syndrome

Definitions & Key takeaways

Nutcracker syndrome is a condition in which the left renal vein is squeezed between the superior mesenteric artery and the aorta, due to a narrow aortomesenteric angle. This results in increased pressure in the left renal vein, which can lead to hematuria and flank pain as well as a left-sided varicocele in people with testicles.

Nutcracker syndrome is diagnosed with imaging tests such as ultrasound or CT scan. The treatment may simply be weight gain, because as the mesenteric fat pad gets fatter, it widens the aortomesenteric angle, thus relieving the compression on the left renal vein. Sometimes surgery is the best treatment option to relieve the compression on the left renal vein.

Watch video only
Renal nutcracker syndrome is when the left renal vein, which drains blood from the left kidney gets squeezed between two large arteries: the superior mesenteric artery and abdominal aorta.
It’s kind of like the renal vein is the nut and the two arteries are the nutcracker. Now, blood heading toward the lower body exits the left ventricle, swoops around the aortic arch, and then flows downward through the descending aorta, which is a large, muscular blood vessel about as thick as a thumb.
The descending aorta runs along the back of the abdominal wall next to the spine, where it is called the abdominal aorta, until it splits into the common iliac arteries.
The abdominal aorta gives rise to many smaller arteries, including three unpaired arteries—the celiac artery, the superior mesenteric artery, and the inferior mesenteric artery—all three of these branch off the anterior wall and supply blood to the digestive tract.
It turns out that the renal vein which carries the blood returning from the kidney to the heart, passes right between the aorta and the superior mesenteric artery.
The angle formed between these two vessels is called the aortomesenteric angle and it’s usually around 45 degrees, with the renal vein cushioned by a bit of fat in the mesentery.
If that aortomesenteric angle is reduced, the arteries begin to pinch the left renal vein like a nutcracker, preventing blood from returning back to the heart.
This leads to a back of blood in the left kidney and renal hypertension. Over time, the high pressures can cause small breaks in the renal blood vessels, and a bit of blood can even get into the urine.
Also, the left testicular vein drains into the left renal vein, so in men blood ends up backing into the left testicle as well.
In young people, reduction of the aortomesenteric angle can happen due to normal growth as well as changes in body proportions.
As a result, sometimes the angle can widen just as easily as it narrowed. In adults, the most common cause is extreme weight loss as the result of severe or prolonged illness—like cancer, HIV/AIDS, drug use, and anorexia nervosa.
Regardless of the cause, nutcracker syndrome typically results in left flank pain and hematuria - or blood in the urine.
The backup of blood on the left can also cause a varicocele in men, which is engorgement of the testicular veins, in this case the left testicular veins.
Nutcracker syndrome can be diagnosed by imaging the left renal vein with something like an ultrasound, and then measuring the blood flow and the aortomesenteric angle, which can get as narrow as 6 degrees.
The main treatment is simply weight gain, because when the mesenteric fat pad gets fatter, it widens the aortomesenteric angle, relieving the left renal vein compression.
In severe situations, where gaining weight doesn’t do the trick - surgery may be needed to move the vein place a stent within the vein to keep it open.
All right, as a quick recap...nutcracker syndrome is when the left renal vein is squeezed between the superior mesenteric artery and the aorta, because the aortomesenteric angle gets too narrow.
This causes increased pressure in the left renal vein which can lead to hematuria and flank pain as well as a left sided varicocele in men.
Nutcracker syndrome can be corrected with weight gain, and sometimes if necessary, surgery.