Horseshoe kidney, also known as ren arcuatus (in Latin), renal fusion or super kidney, is a congenital disorder affecting about 1 in 500 people that is more common in men, often asymptomatic, and usually diagnosed incidentally. In this disorder, the patient's kidneys fuse to form a horseshoe-shape during development in the womb. The fused part is the isthmus of the horseshoe kidney. The abnormal anatomy can affect kidney drainage resulting in increased frequency of kidney stones and urinary tract infections as well as increase risk of certain renal cancers.

Signs and symptoms

thumb|Axial CT image of the abdomen showing a horseshoe kidney.

Although often asymptomatic, the most common presenting symptom of patients with a horseshoe kidney is abdominal or flank pain. However, presentation is often non-specific.

  • Kidney infections – associated with vesicoureteral reflux (present in approximately 50% of all patients with renal fusion) which is an abnormal reflux of urine back into the ureters that increases risk of urinary tract infections. It is estimated 36% of patients with horseshoe kidneys will develop kidney stones.
  • Kidney cancer – increased frequency of certain renal cancers such as transitional cell tumors, Wilms tumors, and carcinoid tumors.
  • Neurological abnormalities - encephalocoele, myelomeningocele, spina bifida. Impairment of a developing embryo's nephrogenic cell migration or abnormal migration of the kidneys due to fetal structural abnormalities is another potential factor. However, this is present in only 40% of cases, and, in 20% of cases, the fused kidney remains in the pelvis. Additionally, during normal development, the kidneys undergo a 90 degree medial rotation while ascending. However, due to the renal fusion, this rotation is impaired resulting in abnormal placement of the ureters. This in turn can lead to urinary stasis and drainage issues.

Diagnosis

Horseshoe kidneys are commonly diagnosed incidentally on abdominal imaging. The diagnosis can be made with many different imaging modalities such as ultrasound, intravenous pyelogram, CT, and MRI.

  • Position of fused kidneys are lower than normal with incomplete medial rotation

Treatment

Symphysiotomy, which involves separating the fused isthmus in order to release the kidneys, used to be a recommended treatment for this condition but has fallen out of favor due to complications and minimal benefit. Furthermore, kidneys can remain in their original abnormal location after the surgery. Instead, management focuses on treating the sequelae should the patient become symptomatic.

While treatment typically does not differ from that of patients with normal kidney anatomy, kidney stones can warrant a different approach. Extracorporeal shockwave lithotripsy, a possible treatment for kidney stones, can be less effective in patients with horseshoe kidneys due to the abnormal anatomy causing difficulties with localizing the energy to the stones. Also, due to the kidney obstruction that can commonly occur with this renal fusion, clearance of the resulting stone fragments can also be impaired.

  • Turner Syndrome: 14-20%
  • Down syndrome: <1%

Notable cases

  • Mel Gibson is affected with this condition.
  • Sam Kinison, an American comedian, also had this condition.

References