Renal ectopic and fusion anomalies
- Norman D Rosenblum, MD, FRCP
Norman D Rosenblum, MD, FRCP
- Professor of Pediatrics
- University of Toronto
- Section Editors
- Tej K Mattoo, MD, DCH, FRCP
Tej K Mattoo, MD, DCH, FRCP
- Section Editor — Pediatric Nephrology
- Professor of Pediatrics
- Wayne State University School of Medicine
- Laurence S Baskin, MD, FAAP
Laurence S Baskin, MD, FAAP
- Section Editor — Pediatric Urology
- Frank Hinman, Jr, MD, Distinguished Professorship in Pediatric Urology
- Chief Pediatric Urology
- Professor of Urology and Pediatrics
- UCSF Benioff Children's Hospital
Renal ectopy and fusion are common congenital anomalies of the kidney and urinary tract (CAKUT), and result from disruption of the normal embryologic migration of the kidneys. Although children with these anomalies are generally asymptomatic, some children develop symptoms due to complications, such as infection, renal calculi, and urinary obstruction.
Ectopic and fusion anomalies of the kidney with their associated complications will be reviewed here. An overview and the evaluation of congenital anomalies of the kidney and urinary tract, including radiological investigations, are found separately. (See "Overview of congenital anomalies of the kidney and urinary tract (CAKUT)" and "Evaluation of congenital anomalies of the kidney and urinary tract (CAKUT)".)
Normal embryologic development of the kidney occurs in three stages; pronephros, mesonephros, and metanephros. The last stage, the metanephros forms the permanent kidney and is first detected at five to six weeks of gestation (figure 1). The metanephros is composed of the metanephric mesenchyme and ureteral bud (caudal portion of the mesonephric duct).
The metanephros is initially positioned in the pelvis opposite the sacral somites. Rapid caudal growth results in the migration of the developing kidney from the pelvis to the retroperitoneal renal fossa, which lies on either side of the spine opposite the second lumbar vertebra. As each kidney ascends, it rotates through 90 degrees such that the renal hilum is directed medially as the kidney reaches its final position. Migration and rotation are completed by the eighth week of gestation.
The ascending kidney derives its vascular supply locally from neighboring vessels. As the kidneys reach their permanent position, renal arteries and veins develop and provide vascular support. As a result, ectopic kidneys usually contain numerous small vessels and reflect the continuous changes in blood supply of the developing kidneys during the course of renal ascent.
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