Renal agenesis overview

# Overview
Renal agenesis is the congenital failure of embryonic kidney formation and may either be unilateral (congenital absence of one kidney with usually normal and hypertrophied contralateral solitary kidney) or bilateral (congenital absence of both kidneys which is incompatible with life). Renal agenesis may be isolated or associated with other anomalies and syndromes. Renal agenesis is diagnosed with routine screening with fetal ultrasound. Patients with unilateral renal agenesis (URA) have an increased risk for proteinuria, hypertension, and renal insufficiency. The mortality rate of bilateral renal agenesis (BRA) without prenatal therapy with serial amnioinfusion is 100%, however, further studies are required to assess the outcome, risks, and benefits of serial amnioinfusion.

# Classification
Renal agenesis may be classified as unilateral renal agenesis(URA) or bilateral renal agenesis (BRA). URA is the congenital absence of one kidney and BRA is the congenital absence of both kidneys which is incompatible with life. Renal agenesis may be isolated or associated with other anomalies and syndromes.

# Pathophysiology
Renal agenesis results from the failure of the ureteric bud to form the ureter, renal pelvis and the collecting duct system and the failure of the renal mesenchyme to form nephrons.

# Causes
Renal agenesis may be associated with CAKUT (congenital anomalies of the kidney and urinary tract) or extra-renal anomalies, genetic syndromes or chromosomal disorders, and sequences.

# Epidemiology and Demographics
The general incidence of unilateral renal agenesis (URA) has been reported to be approximately 1 in 2031 individuals. Males are more commonly affected by unilateral renal agenesis (URA) than females. The incidence of bilateral renal agenesis (BRA) is approximately 1 in every 3000 pregnancies. The mortality rate of bilateral renal agenesis (BRA) without prenatal therapy is 100%.

# Screening
Prenatal screening with ultrasound during pregnancy is routinely performed and this has led to an increase in the diagnosis of unilateral renal agenesis (URA).

# Natural History, Complications, and Prognosis
Complications of unilateral renal agenesis (URA) may include signs of renal injury such as: hypertension, microalbuminuria and chronic kidney disease. Prognosis of bilateral renal agenesis (BRA) is extremely poor, and the mortality rate is 100% without prenatal therapy with serial amnioinfusion.

# Diagnosis

## History
Maternal history during pregnancy for uncontrolled diabetes and treatment for hypertension may be important in unilateral renal disease (URA). Checking the family history of patients with URA for URA, CAKUT (congenital anomalies of the kidney and urinary tract), end stage renal disease (ESRD), and consanguinity may be important.

## Symptoms and Physical Examination
Follow up with checking of blood pressure (for hypertension) and urinalysis (for proteinuria and renal insufficiency) should be considered in patients with unilateral renal agenesis (URA). Checking for other contralateral congenital anomaly of kidney or urinary tract (CAKUT) such as VUR (vesicoureteral reflux) and PUJO (pelviureteric junction obstruction), extra-renal anomalies in different organs (such as cardiac, lung, gastrointestinal, genital, skeleton, and vertebral) , and associated syndromes and sequences (such as VACTERL, CHARGE and Trisomy 18) should be considered when URA is diagnosed.

## CT
Postnatal abdominal CT scan  in patients with unilateral renal agenesis (URA) shows no renal parenchyma.

## MRI
Prenatal MRI may be used for evaluating oligohydramnios, anhydramnios, fetal pulmonary hypoplasia and lung volumes. Postnatal MRI may be helpful in differentiating unilateral renal agenesis (URA) from multicystic dysplastic kidney (MCDK) or renal ectopia.

## Ultrasound
Renal agenesis is diagnosed with routine screening with fetal ultrasound. Renal ultrasonography shows no renal parenchyma in unilateral renal agenesis (URA). Ultrasound findings in bilateral renal agenesis (BRA) may include: absence of fetal kidneys in the renal fossa, empty bladder and anhydramnios after 16 weeks of gestation. Absence of renal arteries on color doppler ultrasonography indicates bilateral renal agenesis (BRA) and may be used as an additive diagnostic tool.

## Other Imaging Findings
Postnatal  renal scintigraphy in patients with unilateral renal agenesis (URA) shows no renal function and may be helpful in differentiating unilateral renal agenesis (URA) from multicystic dysplastic kidney (MCDK) or renal ectopia. 

## Other Diagnostic Studies
There are no other diagnostic studies associated with renal agenesis.

# Treatment

## Medical Therapy and Surgery
Patients with unilateral renal agenesis (URA may progress to renal insufficiency that may progress to end stage renal disease (ESRD) and therefore may require medical treatment  or renal replacement therapy. Early diagnosis of unilateral renal agenesis (URA) and immediate intervention is helpful in controlling the progression to renal insufficiency. The mortality rate of bilateral renal agenesis (BRA) without prenatal therapy with serial amnioinfusion, however is 100%, however, further studies are required to assess the outcome, risks and benefits of serial amnioinfusion, infancy dialysis  and  kidney transplantation.

## Primary Prevention
There are no established measures for the primary prevention of renal agenesis.

## Secondary Prevention
There are no established measures for the secondary prevention of renal agenesis.

## Cost-Effectiveness of Therapy
There is insufficient evidence about the cost-effectiveness of therapy in renal agenesis.

## Future or Investigational Therapies
Intervention with serial amnioinfusion in bilateral renal agenesis (BRA) requires further clinical trials, and further research is needed to assess the long-term outcome of infant dialysis and  renal transplantation.