Nutcracker Syndrome Symptoms: Flank Pain, Blood in Urine and Pelvic Congestion

Nutcracker syndrome symptoms happen when the vein draining the left kidney is squeezed and blood backs up behind the narrowing. The pressure can push blood into the urine, cause an ache in the left side, and force blood down other veins into the pelvis or scrotum. This page goes through each symptom, who tends to get them, how doctors tell a real problem from a harmless scan finding, and when to seek help. For the condition itself and its treatment, see our main guide to nutcracker syndrome.

Why the symptoms happen

The left renal (kidney) vein normally passes between the aorta and another artery, the superior mesenteric artery, on its way to the main vein in the abdomen. If that gap is tight, pressure builds in the kidney vein. Blood then looks for other routes out, mainly down the left ovarian vein in women or the left testicular vein in men. Almost every symptom traces back to that raised pressure and those detours.

The main symptoms of nutcracker syndrome

Blood in the urine (haematuria)

This is the most common sign. Tiny, fragile veins around the kidney can leak into the urine-collecting system. The blood may be:

• Visible, turning urine pink, red or cola-coloured, sometimes after exercise
• Microscopic, found only on a urine dipstick or lab test

It can come and go. Repeated bleeding over a long time can occasionally cause anaemia, leaving you tired and pale.

Left flank pain

An ache in the left flank, the side of the back just below the ribs, is the other classic symptom. It may spread to the left side of the tummy or towards the groin, and often gets worse when standing, walking or exercising.

Protein in the urine on standing

Some people, mostly children, teenagers and young adults, leak protein into their urine when upright but not when lying down. This is called orthostatic proteinuria. It usually causes no symptoms and is found on a routine urine test. Doctors may compare a first-morning sample with a daytime one.

Pelvic congestion in women

When blood is forced down the left ovarian vein, the pelvic veins can widen. This causes pelvic congestion syndrome symptoms such as a dull, dragging pelvic ache, painful periods, pain during or after sex, and varicose veins around the vulva or upper thigh.

A varicocele in men

In men, backed-up blood can widen the veins around the left testicle, forming a varicocele. It may feel like a soft “bag of worms” above the testicle, or cause a dragging ache. A varicocele that appears only on the left side in a young man is a common reason doctors look at the kidney vein.

Less common symptoms

Some people report tiredness, dizziness or a fast heartbeat on standing. The link with nutcracker syndrome is less clear, and these symptoms have many other causes.

Nutcracker syndrome in females

Nutcracker syndrome appears to be somewhat more common in women, and it is most often diagnosed in teenagers and young adults, especially people who are tall and slim or who have recently lost weight. In women, pelvic symptoms may be the main problem rather than blood in the urine. Pain may get worse before a period. Hormones are thought to play a part, but this is not fully understood.

Nutcracker syndrome pain after eating

Pain after meals is not a typical nutcracker symptom. It is more characteristic of SMA syndrome, where the same artery presses on part of the bowel, causing fullness, nausea, vomiting and weight loss after eating. The two can occur together, because both are linked to a narrow angle between the arteries. Read more in how nutcracker and SMA syndrome differ.

Nutcracker syndrome vs normal: the overdiagnosis problem

A narrowed left kidney vein is a fairly common scan finding. In one study of 1,000 routine abdominal CT scans, about 4% showed the narrowing, and most of those people had no related symptoms. Doctors call a narrowing without symptoms nutcracker phenomenon. It is not a disease and does not need treatment.

Nutcracker syndrome should only be diagnosed when:

• Your symptoms fit
• Tests show a real narrowing with signs of backed-up pressure
• More common causes have been ruled out

What else could cause these symptoms?

Blood in the urine always needs checking. Possible causes include urine infection, kidney stones, kidney inflammation (glomerulonephritis), an enlarged prostate in men and, especially in people over about 40, cancers of the kidney or bladder. Left flank pain can also come from kidney stones, infection, muscle strain or spine problems. Pelvic pain has many causes, including endometriosis. See our wider guide to pelvic venous disorders for how vein problems fit together.

How it is confirmed: ultrasound, CT and venogram

Nutcracker syndrome ultrasound

Doppler ultrasound is usually the first scan. It is painless, quick and uses no radiation. The sonographer looks at the left renal vein as it passes under the artery and measures:

• Blood speed. In nutcracker syndrome, blood speeds up sharply through the narrowing. A rise of roughly four to five times compared with the speed near the kidney is a commonly used cut-off.
• Vein width. The vein is usually much wider before the narrowing than at it.

These nutcracker syndrome ultrasound criteria differ a little between centres. Results can change with body position and breathing, and ultrasound is harder in people with more abdominal fat or gas.

CT and MRI

CT or MR scans show the angle between the aorta and the artery, how flattened the vein is, and whether there are swollen veins around the kidney or a widened ovarian vein. They also look for other causes of symptoms.

Venogram with pressure measurement

A venogram passes a thin tube into the kidney vein to measure the pressure difference across the narrowing. It is the most direct test but is invasive, so it is usually saved for unclear cases or when treatment is being planned.

Children and teenagers often improve as they grow, so many people are watched rather than treated. Our guide to nutcracker syndrome treatment explains the options. A Singapore vascular surgeon’s overview of pelvic congestion syndrome describes how kidney vein compression is considered when pelvic veins are assessed.

When to see a doctor

See a doctor if you notice blood in your urine, even once, if a urine test shows blood or protein, or if you have ongoing pain in your left side or back. Also see a doctor about a dull pelvic ache or a swollen vein above the testicle. You can use our pelvic symptom check to organise your thoughts before an appointment.

Get urgent medical help if you pass large amounts of blood or clots in your urine, cannot pass urine, have severe flank pain with fever or vomiting, or feel faint. In Singapore, call 995 in an emergency.

This article is general information, not personal medical advice. Please speak to a doctor about your own symptoms. How we create our content.