The nutcracker syndrome (NCS) results most commonly from the compression of the left

renal vein The renal veins are large-calibre veins that drain blood filtered by the kidneys into the inferior vena cava. There is one renal vein draining each kidney. Because the inferior vena cava is on the right half of the body, the left renal vein is lo ...

(LRV) between the

abdominal aorta In human anatomy, the abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta (of the thorax). Structure The abdominal aorta begins at the level of the diaphr ...

(AA) and

superior mesenteric artery In human anatomy, the superior mesenteric artery (SMA) is an artery which arises from the anterior surface of the abdominal aorta, just inferior to the origin of the celiac trunk, and supplies blood to the intestine from the lower part of the du ...

(SMA), although other variants exist. The name derives from the fact that, in the

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divid ...

and/or

transverse plane The transverse plane (also known as the horizontal plane, axial plane and transaxial plane) is an anatomical plane that divides the body into superior and inferior sections. It is perpendicular to the coronal and sagittal planes. List of cli ...

, the SMA and AA (with some imagination) appear to be a

nutcracker A nutcracker is a tool designed to open nuts by cracking their shells. There are many designs, including levers, screws, and ratchets. The lever version is also used for cracking lobster and crab shells. A decorative version portrays a person w ...

crushing a nut (the renal vein). Furthermore, the venous return from the left gonadal vein returning to the left renal vein is blocked, thus causing testicular pain (colloquially referred to as "nut pain"). There is a wide spectrum of clinical presentations and diagnostic criteria are not well defined, which frequently results in delayed or incorrect diagnosis. The first clinical report of Nutcracker phenomenon appeared in 1950. This condition is not to be confused with superior mesenteric artery syndrome, which is the compression of the third portion of the duodenum by the SMA and the AA.

Signs and symptoms

The signs and symptoms of NCS are all derived from the outflow obstruction of the left renal vein. The compression causes renal vein hypertension, leading to

hematuria Hematuria or haematuria is defined as the presence of blood or red blood cells in the urine. “Gross hematuria” occurs when urine appears red, brown, or tea-colored due to the presence of blood. Hematuria may also be subtle and only detectable w ...

(which can lead to

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

) and

abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Common causes of pain in the abdomen include gastroenteritis and irritable bowel syndrome. About 15% of people have a m ...

(classically left flank or

pelvic pain Pelvic pain is pain in the area of the pelvis. Acute pain is more common than chronic pain. If the pain lasts for more than six months, it is deemed to be chronic pelvic pain. It can affect both the male and female pelvis. Common causes in include ...

). The abdominal pain may improve or worsen depending on positioning. Patients may also have orthostatic proteinuria, or the presence of protein in their urine depending on how they sit or stand. Since the left gonadal vein drains via the left

, it can also result in left

testicular A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosteron ...

pain in men or left lower quadrant pain in women, especially during intercourse and during menstruation. Occasionally, the gonadal vein swelling may lead to ovarian vein syndrome in women.

Nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...

and

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenter ...

can result due to compression of the splanchnic veins. An unusual manifestation of NCS includes

varicocele varicocele is an abnormal enlargement of the pampiniform venous plexus in the scrotum. This plexus of veins drains blood from the testicles back to the heart. The vessels originate in the abdomen and course down through the inguinal canal as p ...

formation and

varicose veins Varicose veins, also known as varicoses, are a medical condition in which superficial veins become enlarged and twisted. These veins typically develop in the legs, just under the skin. Varicose veins usually cause few symptoms. However, some indiv ...

in the lower limbs. Another clinical study has shown that nutcracker syndrome is a frequent finding in varicocele-affected patients and possibly, nutcracker syndrome should be routinely excluded as a possible cause of varicocele and pelvic congestion. In women, the hypertension in the left gonadal vein can also cause increased pain during menses.

Cause

In normal anatomy, the LRV travels between the SMA and the AA. Occasionally, the LRV travels behind the AA and in front of the spinal column. NCS is divided based on how the LRV travels, with anterior NCS being entrapment by the SMA and AA and posterior NCS being compression by the AA and spinal column. NCS can also be due to other causes such as compression by pancreatic cancer, retroperitoneal tumors, and abdominal aortic aneurysms. Although other subtypes exist, these causes are more uncommon in comparison to entrapment by the SMA and the AA. Patients with NCS have a tendency to have a tall and lean stature, as this can lead to a narrower gap between the SMA and the AA for the LRV.

Diagnosis

Nutcracker syndrome is diagnosed through imaging such as doppler ultrasound (DUS), computed tomography (CT), magnetic resonance imaging (MRI), and venography. The selection of the imaging modality is a step-wise process. DUS is the initial choice after clinical suspicion based on symptoms. CT and MRI are used to follow up afterwards, and if further confirmation is necessary, venography is used to confirm.

Doppler Ultrasound

Although its ability to detect renal vein compression is dependent on how a patient is positioned during imaging, DUS is recommended as an initial screening tool as it has a high sensitivity (69–90%) and specificity (89–100%). DUS measures the anteroposterior diameter, and a peak systolic velocity at least four times as fast as an uncompressed vein is indicative of NCS.

CT and MRI

CT and MRI can be used afterward to confirm compression by the AA and SMA with comprehensive measurements of the abdominal vasculature. A "beak sign" can often be seen in CT scans due to the LRV compression. However, CT and MRI cannot demonstrate the flow within the compressed vein. These two modalities can be used to confirm other evidence for NCS such as back-up of blood flow into the ovarian veins.

Venography

If further confirmation is necessary, venography is used as the gold standard test in diagnosing nutcracker syndrome. A renocaval pullback mean gradient of >3 mmHg is considered diagnostic. Although this method continues to be the gold standard, values in unaffected individuals may be vary considerably, leading to some measurements in NCS patients to be similar to those in normal individuals. This may be partly due to compensatory mechanisms in the vasculature as a result of the increased blood pressure. The invasive nature of the procedure is another consideration in comparison to DUS and CT/MRI as imaging modalities.

Differential diagnosis

Pelvic congestion syndrome Pelvic congestion syndrome, also known as pelvic vein incompetence, is a long term condition believed to be due to enlarged veins in the lower abdomen. The condition may cause chronic pain, such as a constant dull ache, which can be worsened by ...

* Renal stones * May-Thurner Syndrome *

Genitourinary The genitourinary system, or urogenital system, are the organs of the reproductive system and the urinary system. These are grouped together because of their proximity to each other, their common embryological origin and the use of common pathw ...

malignancy * Loin pain hematuria syndrome

Treatment

Treatment depends on the severity and symptoms. In addition to conservative measures, more invasive therapies include endovascular stenting, renal vein re-implantation, and gonadal vein embolization. The decision between conservative and surgical management is dependent on the severity of the symptoms. Conservative management is used if the patient is a child and the hematuria is mild. In contrast, more severe symptoms such as reduced renal function, flank pain, and anemia are managed with surgical interventions.

Conservative management

Conservative management is advised in children as further growth may lead to an increase in tissue at the fork between the SMA and AA, providing room for the LRV to pass blood without obstruction. Treatment in this case involves weight gain to build more adipose tissue, decreasing the compression. Venous blood may also be directed towards veins formed as a result of the higher blood pressure, which may contribute to symptomatic relief for individuals as they age. 75% of adolescent patients have been found to have their symptoms resolved after two years. Medications that decrease blood pressure such as

ACE inhibitor Angiotensin-converting-enzyme inhibitors (ACE inhibitors) are a class of medication used primarily for the treatment of high blood pressure and heart failure. They work by causing relaxation of blood vessels as well as a decrease in blood volum ...

s can also be used to reduce the proteinuria.

Surgical management

Open and laparoscopic procedures

There are several different procedures available to manage NCS include: * LRV transposition: The LRV is moved higher in the abdomen and re-implanted to the inferior vena cava (IVC) so that it is no longer being compressed. * Gonadal vein transposition: The gonadal veins are connected to the (IVC) to reduce the amount of blood backed up in the pelvis. * Renocaval bypass with saphenous vein: a segment of the great saphenous vein is used as a second connection between the LRV and the IVC to alleviate pressure build up. * Renal autotransplantation: transfer of a kidney from its original location into the body to another location to prevent venous compression. LRV transposition is the most common procedure done followed by renal autotransplantation and LRV bypass. In all cases for open procedures, data is limited for long term follow-up. With respect to LRV transposition, most patients stated improvement of symptoms 70 months following the procedure. Laparoscopic procedures involve laparoscopic spleno-renal venous bypass and laparoscopic LRV-IVC transposition. They are uncommon in comparison to open procedures, but the outcomes of such procedures are similar to those of open procedures. Although robotic surgery is possible, data on robotic procedures is limited concerning outcomes and cost-effectiveness.

Endovascular procedures

Endovascular interventions involve the use of stents to improve blood flow in the area of LRV impingement. Following catheterization, venography is done to visualize the vasculature and can provide confirmatory diagnosis of NCS prior to stenting. Following stenting, 97% of patients have had improvement of symptoms by sixth months following the procedure, and long term follow-up showed no recurrence of symptoms after 66 months. Although less invasive, risks involved include incorrect placement of the stent as well as stent dislodging and migration to the right atrium. Furthermore, patients must be on anticoagulation therapy after stenting for three months.

Gallery

File:NutCracker1.PNG, Compression of the

left renal vein The renal veins are large-calibre veins that drain blood filtered by the kidneys into the inferior vena cava. There is one renal vein draining each kidney. Because the inferior vena cava is on the right half of the body, the left renal vein is lo ...

(marked by the arrow) between the

(above) and the aorta (below) due to nutcracker syndrome File:NutCracker2.PNG,

Thrombosis Thrombosis (from Ancient Greek "clotting") is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (th ...

in the left renal vein associated with dilation File:Renal Nutcracker Syndrome.webm, Summary video explaining signs and symptoms as well as etiology of nutcracker syndrome File:Nutcracker - tool (PSF).png, alt=Drawing of a simple, hand-held nutcracker, A

. The legs of this nutcracker, with some imagination, could represent the two arteries, squeezing whatever is stuck between them.

References

External links

* {{Urologic disease Kidney diseases Syndromes Vascular diseases