Nutcracker syndrome: symptoms, causes, diagnosis and treatment

The left kidney drains blood through the left renal vein, which passes between the aorta and one of its branches, the superior mesenteric artery (SMA), on its way to the inferior vena cava. In some people that gap is narrow, and the vein is squeezed. A case-based review explains that the earliest anatomical description, by Grant in 1937, likened the vein to a nut between the jaws of a nutcracker.

The same review separates the finding from the condition. The nutcracker phenomenon is the compression seen on imaging, which may be an incidental finding. Nutcracker syndrome is when symptoms arise from it. A second review adds that the majority of nutcracker phenomenon cases remain asymptomatic and undiagnosed, and are frequently found incidentally during imaging for other reasons.

The reviews also describe a less common posterior variant, in which a retro-aortic or circum-aortic renal vein is compressed between the aorta and the vertebral body.

The reviews describe the constellation as haematuria, flank or pelvic pain, orthostatic proteinuria (protein in the urine that appears when upright) and, in male patients, varicocele. A second review notes that the most frequent symptoms are left flank pain, varicocele, proteinuria and anaemia, and that the symptoms are non-specific and often presented in primary care.

The same review lists other possible symptoms including syncope, fever, orthostatic intolerance, painful periods, painful urination and pain during intercourse. It describes a renal presentation (haematuria, proteinuria and left flank pain) and a second group that includes varicocele, abdominal pain and pain during intercourse.

In severe cases, engorged pelvic veins may produce pelvic pain, fullness or discomfort, described in the case-based review as pelvic congestion syndrome.

In the commonest form, a narrow angle between the aorta and the SMA squeezes the vein. The case-based review says the normal aortomesenteric angle ranges between 40 and 90 degrees and varies with age and visceral fat. Less common causes of compression include a pancreatic tumour, enlarged lymph nodes, lordosis and low retroperitoneal and mesenteric fat.

The review explains that the raised pressure in the vein causes venous congestion and engorgement of small veins around the ureter and kidney pelvis, which can rupture and cause microscopic or macroscopic haematuria. It also describes how the pressure may lead to orthostatic proteinuria and pain.

Because there are no consensus criteria, the diagnosis is made by excluding other causes of blood in the urine and pain. The review says a history of haematuria and flank pain may prompt urine studies, such as urinalysis, microscopy, culture and cytology, and that Doppler ultrasonography, CT and MRI are all reasonable first-line radiological studies. It adds that variations of normal anatomy may be seen and should not immediately prompt a diagnosis.

Retrograde venography, sometimes with intravascular ultrasound, is described as the gold standard, with an elevated pressure gradient between the left renal vein and the vena cava confirming venous hypertension; a gradient of 3 mmHg or more is the standard reference point. The review reports that Doppler ultrasound has a sensitivity of 69% to 90% and specificity of 89% to 100%, but findings vary with technique and positioning.

The second review stresses that nutcracker syndrome is worth considering especially in the differential diagnosis of haematuria of unknown origin. Because the symptoms overlap with more common problems, the usual tests for blood in the urine come first.

Treatment can be conservative or surgical, depending on the severity of symptoms and the degree of vein compression, according to the second review. The case-based review cites a series of children and young people in which conservative treatment resolved symptoms in 16 of 21 (76%), with 5 needing surgery, and another series in which just over two-thirds improved on conservative treatment, with low-dose aspirin used in some.

Open surgical approaches include transposing the left renal vein, patch venoplasty, nephropexy, gonadal vein transposition and kidney autotransplantation. The review says endovascular stenting of the vein is becoming a preferred modality because it is minimally invasive, with series reporting symptoms improving or resolving in the large majority, and a main complication of stent migration, which is rare.

The choice between these depends on the severity of symptoms and the degree of vein compression, so decisions rest on specialist judgement.

Blood in the urine is the symptom most likely to bring someone to a doctor, and the NHS is clear about what to do. It says that if you think you have blood in your pee you need to get it checked, even if there is only a small amount or you are not sure it is blood, and to ask for an urgent GP appointment or get help from NHS 111.

The NHS adds that blood in your pee must be checked because it can be a sign of cancer, which may be easier to treat if found early. A GP will ask about your symptoms, may arrange a urine sample or blood test and may refer you to a specialist for tests, so the usual tests for blood in the urine come first, and nutcracker syndrome is considered when the common causes are excluded.

Visible blood in the urine should always be reported to a GP.

The reviews describe a condition that is rare, easily missed and with variable severity. Pain and the uncertainty of an unusual diagnosis can be wearing, and it is reasonable to ask for referral to a centre with experience of the condition if symptoms persist without an explanation.

No NHS or UK charity patient page on nutcracker syndrome was available when this guide was prepared. The information here is drawn from two published clinical reviews, written for clinicians. They are not UK guidelines, and practice in the UK may differ, so the details above should be discussed with your own specialist team.