What is a horseshoe kidney?
A horseshoe kidney, also called renal fusion, is when two kidneys are fused or joined together. They form a shape like a horseshoe. A horseshoe kidney is also in a different location compared to two typical kidneys. It’s located lower in the tummy and closer to the front of your body.
But they work normally. In other words, someone with a horseshoe kidney has two working kidneys that have grown together (in a U-shape). Both kidneys have their own blood vessels and ureter.
A horseshoe kidney usually does not cause any problems, or symptoms. Some people experience urinary tract infections (UTIs), or pain when urinating, or kidney stones and blood in the urine.
How common is a horseshoe kidney?
It is not known as most people do not experience symptoms. The estimates vary widely – from 1 in 500 to 1 in 10,000 people. However horseshoe kidneys occur approximately twice as often in men than in women.
What causes horseshoe kidneys?
A horseshoe kidney is a congenital defect. This means that the horseshoe kidney is already present at birth.
In an unborn child, the kidneys develop in the pelvis. In the 5th and 6th week of pregnancy, the kidneys are very close together. If the undersides of the kidneys touch each other, a connection can grow. The connection is called a bridge. The fusion of the kidneys is called renal fusion. This is how a horseshoe kidney is created.
In the 7th or 8th week of pregnancy the kidneys move upwards. A horseshoe kidney also goes upwards, but usually less far. This is due to the part that has grown together. This ‘bridge’ between the kidneys gets caught under an artery.
The kidneys develop early in pregnancy.
It is not known why the kidneys of one foetus grow together and not of another.
Hereditary disorders
Sometimes a horseshoe kidney is part of another hereditary condition. Horseshoe kidneys occur in the following hereditary conditions:
Chromosomal conditions:
- Downs syndrome
- Turners syndrome
- Trisomy 13 (Patau syndrome)
- Trisomy 18 (Edwards syndrome)
- Williams syndrome.
Nonchromosomal conditions:
- Ellis-van Creveld syndrome
- Fanconi anaemia
- Goltz syndrome
- Kabuki syndrome
- Pallister-Hall syndrome
- VACTERL association
- Coffin Siris
- Goldenhar syndrome
- Meckel syndrome
- Roberts syndrome.
About 6 in 10 children with Turner syndrome have a horseshoe kidney. It is less common with other conditions.
Most of these conditions are rare or very rare. The kidneys usually also function normally for people with these syndromes. Children with these syndromes often have other problems, sometimes serious.
Symptoms of a horseshoe kidney
Most people with a horseshoe kidney have no symptoms. If people do experience symptoms from a horseshoe kidney, they may include:
- Abdominal (tummy) pain
- Nausea
- Kidney stones
- Urinary tract infections (UTIs), such as a bladder or kidney infection
- Abdominal (belly) pain
- Blood in the urine (haematuria)
- Pain when you pee.
Why infections? The urine cannot leave the kidney as easily. Bacteria then easily move from the urethra and bladder to the kidney. In a horseshoe kidney, the connection of the ureters to the bladder may also be different. This makes it easier for urine to flow back from the bladder into the ureter. This increases the risk of an infection.
Why stones? Because the urine remains stagnant for longer than normal, small crystals can clump together in the urine – eventually forming stones. Kidney stones cause pain and blood in the urine.
What are the complications of horseshoe kidney?
People with horseshoe kidney are more prone to developing:
- Vesicoureteral reflux (VUR), when urine flows backward from your bladder back toward your kidneys
- Ureteropelvic junction (UPJ) obstruction, when part of your kidney and urine drainage is blocked.
- Hydronephrosis, a collection of urine in the center of the kidneys, makes the kidneys swell.
- Renovascular hypertension, i.e. high blood pressure that happens when the arteries that carry blood to your kidneys narrow.
- Wilms tumour, a type of kidney tumor that happens in children
- Recurrent urinary tract infection, kidney stones and chronic hydronephrosis can cause permanent damage to the kidneys, leading to CKD. This is rare.
Increased risk of kidney cancer
As stated above, people with a horseshoe kidney may have a slightly higher risk of Wilms tumour, a form of kidney cancer. The risk is twice as high as in children without a horseshoe kidney. In the past, a horseshoe kidney was found remarkably often in children with Wilms tumour. But that does not mean that the horseshoe kidney is the cause of the cancer. Most children with a Wilms tumour recover completely. Wilms tumour is rare in adults.
Diagnosis of a horseshoe kidney
Children may be known to have a horseshoe kidney before birth. It can be seen on the 20-week ultrasound in pregnancy. You then know that your child will be born with a horseshoe kidney. After birth, your baby will receive an ultrasound so that the doctor can see whether the urine is flowing properly. If the doctor is unsure, an additional kidney scan may be necessary.
As an older child or adult, a horseshoe kidney can be found by chance – for example, if you have an ultrasound or CT scan due to another condition.
It may also happen if your doctor thinks you have a horseshoe kidney. For example, because you often have bladder infections or kidney stones. The doctor will then refer you to a urologist (kidney surgeon).
Treatment of a horseshoe kidney
There is no cure for horseshoe kidney. If you’re not having symptoms, you will not need any treatment.
If you’re having symptoms, your doctor can offer treatments to improve symptoms. For example, antibiotics can treat a bacterial infection.
Surgery can be needed to:
- Restore urine flow
- Correct vesicoureteral reflux
- Remove kidney stones.
Most people with a horseshoe kidney require no treatment.
Horseshoe kidney surgery
Severe and recurring complaints sometimes require surgery.
Operation to split the horseshoe kidney
For example, occasionally splitting the horseshoe kidney is necessary. The bridge between the kidneys is cut. The operation is possible as keyhole surgery (laparoscopic).
Other things about a horseshoe kidney
Donate a horseshoe kidney
Do you want to be an organ donor after your death? A horseshoe kidney is suitable as a donor kidney. Usually a horseshoe kidney is split so that two kidney patients can be helped. Sometimes a horseshoe kidney is placed entirely in 1 recipient.
Last Reviewed on 7 October 2023