Ectopic Kidney

An ectopic kidney is a congenital positional anomaly in which a kidney is located outside its usual position in the upper posterior abdominal wall. The abnormal position most commonly results from failure or alteration of the normal ascent of the developing kidney from the pelvis into the lumbar region.

The most common form is a pelvic kidney, in which the kidney remains within the pelvis. Ectopic kidneys may also occur at other levels along the normal pathway of renal ascent or, less commonly, cross to the opposite side of the body. Their abnormal position is frequently accompanied by variations in renal rotation, arterial supply, venous drainage, and ureteric anatomy.

Normal Development of the Permanent Kidney

The permanent kidneys develop from the metanephroi, which begin forming in the pelvic region during early embryonic development.

Each metanephros develops through interactions between a ureteric bud and the surrounding metanephric mesenchyme.

Initial Position of the Kidneys

The developing metanephric kidneys are initially located relatively close together within the pelvis.

As the embryo grows, the kidneys normally come to occupy progressively higher positions within the posterior abdominal region.

Renal Ascent

The apparent ascent of the kidneys occurs primarily as a consequence of differential growth of the embryonic body, particularly the regions inferior to the kidneys.

The kidneys gradually move from their initial pelvic position toward their definitive lumbar position.

Definitive Renal Position

Normally, the kidneys ultimately lie retroperitoneally on the posterior abdominal wall on either side of the vertebral column.

The right kidney is typically positioned slightly lower than the left because of its relationship to the liver.

Normal Renal Rotation

As the kidneys ascend, they also undergo rotation.

The renal hila initially face relatively anteriorly but normally rotate toward a more medial orientation as development proceeds.

Development of an Ectopic Kidney

An ectopic kidney develops when the normal process of renal ascent is interrupted or altered.

The final location depends on where the kidney remains during its developmental migration.

Pelvic Kidney

A pelvic kidney results when a developing kidney fails to ascend from the pelvis.

It may remain near the common iliac vessels, internal iliac vessels, pelvic brim, sacrum, or other pelvic structures depending on its exact position.

Pelvic Relationships

A pelvic kidney may lie anterior to the sacrum and below the normal lumbar renal position.

Its relationships to the bowel, reproductive organs, pelvic vessels, bladder, and other pelvic structures differ substantially from those of a normally positioned kidney.

Low Abdominal Kidney

Some ectopic kidneys ascend partially but fail to reach the usual renal fossa.

These kidneys may occupy a low abdominal or iliac position between the pelvis and the normal lumbar renal location.

Crossed Renal Ectopia

Crossed renal ectopia occurs when one kidney is located on the opposite side of the body from the side on which its ureter enters the bladder.

The ureter of the ectopic kidney typically crosses the midline before reaching its normal side of insertion into the urinary bladder.

Crossed Fused Renal Ectopia

In many cases of crossed renal ectopia, the ectopic kidney is fused with the normally positioned kidney on the opposite side.

This arrangement is called crossed fused renal ectopia.

Crossed Unfused Ectopia

Less commonly, the crossed kidney remains anatomically separate from the kidney on the side to which it has migrated.

This is known as crossed renal ectopia without fusion.

Ureter in Crossed Renal Ectopia

The course of the ureter is an important feature for determining the developmental side of a crossed ectopic kidney.

Although the kidney lies contralaterally, its ureter usually crosses the midline and enters the bladder on the side corresponding to the kidney's embryological origin.

Simple Renal Ectopia

In simple renal ectopia, the kidney remains on its normal side of the body but occupies an abnormal position.

A pelvic kidney is the most familiar example of this pattern.

Renal Malrotation

Ectopic kidneys frequently demonstrate malrotation.

Because renal ascent and rotation occur during overlapping periods of development, interruption of ascent can leave the renal hilum facing anteriorly or in another atypical direction.

Hilum Orientation

In a normally rotated kidney, the renal hilum faces predominantly medially.

In an ectopic kidney, the hilum may face anteriorly, laterally, or in another direction depending on the degree of developmental rotation.

Shape of an Ectopic Kidney

Ectopic kidneys may differ in shape from normally positioned kidneys.

Restricted space, abnormal rotation, fusion, and altered relationships with surrounding structures can influence renal morphology.

Renal Vascular Development

The arterial supply of the developing kidneys changes repeatedly during ascent.

As the kidneys move superiorly, they acquire new arterial branches from progressively higher levels of the aorta while many lower vessels normally regress.

Transient Renal Arteries

During normal ascent, multiple temporary arterial connections may form between the developing kidneys and nearby major arteries.

Persistence of some of these vessels accounts for many accessory and aberrant renal arteries encountered in adult anatomy.

Vascular Supply of a Pelvic Kidney

A pelvic kidney may retain arterial branches from vessels near its abnormal location.

Its blood supply may arise from the distal abdominal aorta, common iliac arteries, internal iliac arteries, external iliac arteries, or combinations of nearby vessels.

Multiple Renal Arteries

Ectopic kidneys commonly have multiple or atypically positioned renal arteries.

The number and origins of these vessels reflect the developmental level at which vascular connections persisted.

Renal Venous Variations

Venous drainage may also differ from the usual pattern.

An ectopic kidney can have multiple renal veins or venous channels draining into iliac veins, the inferior vena cava, or other nearby venous structures.

Surgical Importance of Vascular Variation

Abnormal renal vessels are particularly important during abdominal, pelvic, vascular, and urological surgery.

Unexpected arteries or veins can be injured if the ectopic kidney and its vascular anatomy are not recognized before intervention.

Ureter of an Ectopic Kidney

The ureter connects the ectopic kidney with the urinary bladder.

Because the kidney lies closer to the bladder than usual in pelvic ectopia, the ureter is often shorter than the ureter of a normally positioned kidney.

Ureteric Insertion

In simple renal ectopia, the ureter usually enters the bladder on the expected side.

The major abnormality is therefore the position of the kidney rather than necessarily the distal insertion of its ureter.

Urinary Drainage

An ectopic kidney may drain normally and remain clinically silent throughout life.

However, abnormal orientation of the renal pelvis and ureter can interfere with efficient urinary drainage in some individuals.

Ureteropelvic Junction

Abnormal rotation or positioning may alter the relationship between the renal pelvis and proximal ureter.

This can contribute to impaired drainage at or near the ureteropelvic junction in some ectopic kidneys.

Hydronephrosis

Hydronephrosis is dilation of the renal collecting system caused by impaired urinary drainage.

It may occur in an ectopic kidney when abnormal anatomy produces obstruction or interferes with normal urine flow.

Vesicoureteral Reflux

Vesicoureteral reflux is retrograde flow of urine from the bladder into the ureter and potentially the renal collecting system.

Some patients with renal ectopia have associated abnormalities of the urinary tract that increase the likelihood of reflux.

Urinary Tract Infection

Abnormal drainage, urinary stasis, reflux, or obstruction can predispose an affected individual to urinary tract infection.

Recurrent infections may therefore lead to investigation and discovery of a previously unrecognized ectopic kidney.

Renal Calculi

Urinary stasis can contribute to formation of renal calculi.

Abnormal renal position and collecting-system anatomy may also complicate the diagnosis and treatment of stones within an ectopic kidney.

Renal Function

An ectopic kidney can have normal or near-normal renal function.

Functional impairment is more likely when ectopia is associated with significant dysplasia, obstruction, reflux, recurrent infection, or other urinary tract abnormalities.

Asymptomatic Ectopic Kidney

Many ectopic kidneys produce no symptoms and are discovered incidentally during imaging, surgery, or investigation of an unrelated condition.

The presence of an ectopic kidney alone does not necessarily indicate impaired renal function.

Abdominal Examination

A low-lying ectopic kidney may occasionally be encountered as an unexpected abdominal or pelvic mass.

Its position must be distinguished from other retroperitoneal, abdominal, or pelvic structures.

Pelvic Examination

A pelvic kidney may occupy space near reproductive organs and other pelvic structures.

Recognition of this possibility is important when evaluating an unexpected pelvic mass or planning pelvic procedures.

Pregnancy

A pelvic kidney may have altered relationships with the enlarging uterus and pelvic birth canal.

The clinical importance depends on the kidney's exact position, size, mobility, and relationship to surrounding structures.

Trauma

Normally positioned kidneys receive partial protection from the lower ribs and surrounding posterior abdominal structures.

An ectopic kidney may have different protective relationships and may therefore be exposed to different patterns of injury.

Ultrasound

Ultrasound can identify the absence of a kidney from its expected renal fossa and may locate an ectopic kidney elsewhere in the abdomen or pelvis.

It can also assess renal size, collecting-system dilation, and some associated urinary abnormalities.

Prenatal Detection

Renal ectopia may be recognized during prenatal ultrasonography when a kidney is not visualized in its expected position.

Further imaging can help identify renal tissue within the pelvis or another abnormal location.

Computed Tomography

Computed tomography can define the position, orientation, collecting system, surrounding anatomical relationships, and vascular supply of an ectopic kidney.

This information can be particularly useful before surgical intervention.

Magnetic Resonance Imaging

Magnetic resonance imaging can also demonstrate renal position and relationships without ionizing radiation.

Magnetic resonance techniques may be useful when detailed anatomical evaluation is required.

Functional Imaging

Renal functional studies can evaluate the contribution of an ectopic kidney to overall renal function and assess urinary drainage.

Such information can be important when structural abnormalities or obstruction are present.

Differential Diagnosis of an Empty Renal Fossa

Failure to identify a kidney in its normal location does not by itself establish renal agenesis.

The possibility of an ectopic kidney should be considered and the abdomen and pelvis evaluated for renal tissue in an abnormal location.

Ectopic Kidney and Renal Agenesis

Feature	Ectopic Kidney	Renal Agenesis
Kidney formed	Yes	No kidney on affected side
Normal renal fossa	Empty	Empty
Renal tissue elsewhere	Present	Absent
Primary developmental problem	Abnormal position or ascent	Failure of renal development

Ectopic Kidney and Nephroptosis

An ectopic kidney should also be distinguished from nephroptosis, in which a normally developed kidney is unusually mobile and descends when the individual is upright.

An ectopic kidney occupies an abnormal position because of congenital development rather than acquired mobility.

Horseshoe Kidney

A horseshoe kidney also demonstrates abnormal renal ascent, but its mechanism differs from simple renal ectopia.

In a horseshoe kidney, fusion of the renal poles, usually the lower poles, creates an isthmus that limits normal ascent, classically through interaction with the inferior mesenteric artery.

Ectopic and Horseshoe Kidney Comparison

Feature	Ectopic Kidney	Horseshoe Kidney
Main abnormality	Abnormal renal position	Fusion of kidneys with abnormal ascent
Common location	Pelvis or low abdomen	Lower than normal lumbar position
Fusion	Not required	Present
Rotation	Often abnormal	Often abnormal
Vascular anatomy	Frequently variable	Frequently variable

Crossed Ectopia and Simple Ectopia

Feature	Simple Ectopia	Crossed Ectopia
Kidney side	Remains on side of origin	Located on opposite side
Ureter crosses midline	No	Usually yes
Fusion with opposite kidney	No	Common but not obligatory
Example	Pelvic kidney	Crossed fused renal ectopia

Associated Congenital Abnormalities

Renal ectopia can occur as an isolated anomaly or together with other congenital abnormalities.

Associated abnormalities may involve the urinary tract, reproductive system, vertebral column, or other developmental structures.

Relationship to Reproductive Development

The urinary and reproductive systems develop in close anatomical and embryological association.

Consequently, congenital abnormalities of renal development can occasionally coexist with abnormalities of reproductive tract development.

Surgical Considerations

The position and vascular anatomy of an ectopic kidney should be established before surgery in the relevant abdominal or pelvic region.

Multiple arteries, unusual veins, altered ureteric courses, and unexpected renal parenchyma can substantially change operative anatomy.

Vascular Procedures

Pelvic renal arteries may arise from vessels that are also important targets during vascular surgery.

Preoperative recognition of these branches can help preserve renal perfusion and prevent inadvertent vascular injury.

Pelvic Surgery

A pelvic kidney and its ureter can lie within operative fields used for colorectal, gynecological, urological, and vascular procedures.

Knowledge of the anomaly is therefore important even when the kidney itself is not the target of surgery.

Developmental Sequence

Developmental Event	Normal Result	Possible Abnormal Result
Metanephros forms in pelvis	Early permanent kidney	Kidney remains pelvic if ascent fails
Renal ascent	Kidney reaches lumbar region	Low abdominal or pelvic ectopia
Renal rotation	Hilum becomes medially directed	Malrotation
Changing vascular supply	Definitive renal arterial pattern develops	Persistent aberrant or accessory vessels

Key Anatomical Features

• An ectopic kidney occupies an abnormal congenital position.
• The abnormality usually results from altered renal ascent.
• The developing permanent kidneys initially form within the pelvic region.
• Pelvic kidney is the most common form of renal ectopia.
• A kidney may also remain in a low abdominal or iliac position.
• Crossed renal ectopia places a kidney on the side opposite its embryological origin.
• Crossed ectopic kidneys are frequently fused with the contralateral kidney.
• The ureter of a crossed ectopic kidney usually crosses the midline before entering the bladder.
• Ectopic kidneys frequently demonstrate abnormal rotation.
• The renal hilum may face anteriorly rather than medially.
• Renal arterial supply is frequently variable.
• Pelvic renal arteries may arise from the aorta or iliac vessels.
• Venous drainage may also be anomalous.
• A pelvic kidney generally has a shorter ureter than a normally positioned kidney.
• Many ectopic kidneys are asymptomatic and discovered incidentally.

Clinical Importance

Ectopic kidney is important because abnormal renal position changes the normal relationships of the kidney, ureter, and renal vessels. Although many ectopic kidneys function normally, malrotation and altered collecting-system anatomy can predispose some individuals to urinary obstruction, hydronephrosis, reflux, infection, or stone formation.

The vascular anatomy is particularly important. Because renal arteries develop sequentially during ascent, a kidney that remains at an abnormal level may retain vessels arising from nearby portions of the aorta or iliac arterial system. Multiple arteries and atypical venous drainage must therefore be considered before abdominal, pelvic, or vascular procedures.

Understanding ectopic kidney provides the anatomical and embryological foundation for studying renal ascent, renal rotation, pelvic kidney, crossed renal ectopia, crossed fused renal ectopia, renal vascular variation, hydronephrosis, ureteric abnormalities, and congenital anomalies of the urinary system.