Horseshoe or duplex kidney seen by chance on a scan

What the report means

Each kidney makes urine, which drains through a funnel inside the kidney and then down a tube called the ureter to the bladder. (MedlinePlus) A horseshoe kidney changes how the two kidneys sit; a duplex kidney changes how one kidney drains. Both belong to a group of differences in how the kidneys and urinary tract form before birth. (MedlinePlus Genetics)

Words a report may use (simplified)
Report wording	What it describes
Horseshoe kidney or renal fusion	The two kidneys are joined across the middle of the body, at the lower ends in over 90% (Nechita 2025)
Isthmus	The band joining the two kidneys; it is kidney tissue in about 85% and a fibrous band in the rest (Schiappacasse 2015)(Nechita 2025)
Malrotation or low-lying kidneys	The joined kidneys sit lower and turn differently from usual, so the funnels and ureters point forward or to the side (Muttarak 2012)(Nechita 2025)
Duplex kidney or duplicated collecting system	One kidney with two drainage systems, an upper and a lower part (moiety) (MedlinePlus Genetics)(Kozlov 2020)
Bifid pelvis or bifid ureter (incomplete duplication)	The two drainage systems join into one ureter before the bladder (Kozlov 2020)
Complete duplication	Two separate ureters run from one kidney to the bladder (Kozlov 2020)

How common they are

Horseshoe kidney. Estimates are about 0.25% of people, or 1 in 400 to 600, and anatomy studies give 0.15% to 0.48%. It is about twice as common in men. (Nechita 2025)(Muttarak 2012)(Schiappacasse 2015)
Duplex kidney. Estimates range from 0.2% to 2% of people, and women are affected about twice as often as men. (Kozlov 2020)
Found at any age. A horseshoe kidney may be found in young children with other differences, in young women checked for late periods linked with Turner syndrome, or by chance in adults on a scan for something else. (Nechita 2025) Duplex kidneys are now often seen on scans before birth, and most of the incomplete type are found by chance. (Oshiba 2025)

Why most cause no symptoms

A horseshoe kidney often causes no symptoms in adults. (Nechita 2025) Reviews put the share found by chance at about one-third, or up to 30%. (Muttarak 2012)(Schiappacasse 2015) Duplex kidneys are also often symptom-free. About 40% of people with a duplex kidney have been reported with problems, but the review authors say the true share is likely lower, because the people counted were mostly those who already sought care. (Kozlov 2020)

When symptoms happen, they are usually linked to a blockage, stones or infection. (Muttarak 2012)

What they can be linked with

Horseshoe kidney. The ureters pass in front of the joining band and take an unusual course, which makes blockage more likely. Studies report stones in 20% to 60%, infections in 27% to 41% and a narrowing where the funnel meets the ureter in about 35% of people with a horseshoe kidney, mostly in groups already seen in hospital. (Muttarak 2012)(Schiappacasse 2015) A horseshoe kidney is more easily hurt by a blow to the belly. (Schiappacasse 2015)
Duplex kidney. It is linked with a widened drainage system (hydronephrosis), urine flowing back up from the bladder (reflux), scarring and stones. (Kozlov 2020) A children's series lists more possible problems with complete duplication than with the incomplete type. (Oshiba 2025)
Growths. The most common kidney cancer occurs at about the same rate in a horseshoe kidney as in other kidneys, while some rarer tumours are reported more often. (Schiappacasse 2015)(Muttarak 2012)

These are results from groups of people, many already being seen for a kidney problem, not a forecast for one person.

If the same report says the drainage system is widened, see swollen kidney (hydronephrosis) seen by chance. Small round calcium spots low in the pelvis are covered on pelvic vein stones (phleboliths).

What comes next

Kidney function. NICE says to offer an eGFR blood test and a urine albumin test (ACR) to adults with structural renal tract disease or repeated kidney stones. (NICE NG203) Your doctor decides whether your finding counts. See kidney test results for what the numbers mean.
A closer look when needed. In a study of adults with kidney differences in shape or position, CT showed the anatomy and any complications best, and ultrasound also helped find a horseshoe kidney. (Muttarak 2012)
No set repeat schedule. None of the sources on this page sets a routine schedule of repeat scans for a horseshoe or duplex kidney found by chance without symptoms. Your doctor decides whether any further scan helps.
Earlier scans. Both are present from birth, so an older scan may already show it. Bring dates of earlier scans if you have them.

Your doctor decides which tests fit your report, your symptoms and your earlier results.

Who it applies to

Adults told that an ultrasound or CT done for another reason shows a horseshoe kidney or a duplex kidney. Findings in unborn babies and children follow a different path and are not covered here.

NHS, kidney infection: (NHS)

"Ask for an urgent GP appointment or get help from NHS 111 if" you think you may have a kidney infection and you "have a very high temperature, or feel hot, cold or shivery", "have pain in the lower tummy or in the back, just under the ribs", "have blood in your pee" or "have not had a pee all day".

Call 999 (in the US, call 911) or go to A&E now if "you are confused, drowsy or have difficulty speaking".

Routine age-based screening

No routine screening test looks for a horseshoe or duplex kidney. It ties in with checks that are part of age-based care:

Kidney tests. See kidney disease screening for who is tested and how often.
Other kidney findings. See swollen kidney (hydronephrosis), small or scarred kidney and small kidney mass found by chance.
All screenings by age. See screenings by age and gender.

Where they differ:

How common a horseshoe kidney is. Figures range from 0.15% to 0.48% in anatomy studies, with 0.25% (about 1 in 400 to 600) most often quoted. (Nechita 2025)(Muttarak 2012) Duplex kidney estimates are wider still, 0.2% to 2%. (Kozlov 2020)
How often there are no symptoms. One review says a horseshoe kidney often causes no symptoms in adults; imaging reviews put the share found by chance at about one-third, or up to 30%. (Nechita 2025)(Muttarak 2012)(Schiappacasse 2015) For duplex kidneys, the 40% with problems comes from people already seeking care and is likely an overestimate. (Kozlov 2020)
Cancer risk. One imaging review says the most common kidney cancer is no more frequent in a horseshoe kidney; another calls this debated. Both say some rarer tumours are reported more often. (Schiappacasse 2015)(Muttarak 2012)

Your doctor decides what your result means for you.

Questions people ask

What is a horseshoe kidney?

The two kidneys are joined, usually at their lower ends, by a band of tissue called the isthmus, so together they look like a horseshoe. It is the most common kind of fused kidney and is present from birth. (Nechita 2025) (Schiappacasse 2015)

What is a duplex kidney?

A kidney that has two drainage systems instead of one. MedlinePlus Genetics describes it as an extra ureter leading to the kidney. The two parts may join into one ureter (incomplete) or drain through two separate ureters into the bladder (complete). (MedlinePlus Genetics) (Kozlov 2020)

How common are they?

Horseshoe kidney is reported in about 0.25% of people, roughly 1 in 400 to 600, and about twice as often in men. Duplex kidney is estimated at 0.2% to 2% of people and is about twice as common in women. (Nechita 2025) (Muttarak 2012) (Kozlov 2020)

Do they cause symptoms?

Often not. Both are commonly found by chance on a scan done for another reason. When symptoms do occur, they are usually linked to a blockage, kidney stones or infection. (Nechita 2025) (Muttarak 2012) (Kozlov 2020)

When should I get urgent help?

The NHS says to ask for an urgent GP appointment or get help from NHS 111 for possible kidney infection signs such as a very high temperature, pain in the back just under the ribs or blood in your pee. It says to call 999 (in the US, call 911) or go to A&E if you are confused, drowsy or have difficulty speaking. (NHS)