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Unilateral Renal Agenesis

Definition and Epidemiology

Definition:

Unilateral renal agenesis is the complete absence of renal development on one side, with a normal or compensatorily hypertrophied contralateral kidney.

Epidemiology:

The incidence is 1:1100 to 1:5000. Unilateral renal agenesis is slightly more common on the left side and occurs more often in males.

Etiology

Unilateral renal agenesis results from a developmental disorder of the urogenital ridge, which affects the ureteric bud, mesonephric duct (Wolffian duct), and, depending on its timing and extent, sometimes also the paramesonephric duct (Müllerian duct). Associated malformations of the internal genital organs are common; see the following section.

Pathology and Symptoms

Many affected individuals are asymptomatic, and the diagnosis is often made prenatally or incidentally during ultrasonography. The contralateral kidney frequently shows compensatory hypertrophy. Associated malformations of the urinary tract or genital organs and the long-term consequences of hyperfiltration in the solitary kidney are clinically relevant. Function and structural integrity of the solitary contralateral kidney are decisive for prognosis.

Malformations of the Upper Urinary Tract

The ureter is often completely absent; alternatively, it may be rudimentary and/or insert ectopically. Pathological findings of the contralateral side, such as vesicoureteral reflux, megaureter, duplex ureter, or ureteropelvic junction obstruction, are more common.

Male Genital Organs

In men, ipsilateral malformations of the Wolffian duct system may be present, including aplasia or hypoplasia of parts of the epididymis, vas deferens, seminal vesicle, or ejaculatory duct. If the seminal vesicle is present but obstructed, Zinner syndrome may develop: renal agenesis with an ipsilateral seminal vesicle cyst.

Female Genital Organs

In women, associated Müllerian duct anomalies should be actively investigated, such as a unicornuate uterus with an absent fallopian tube or complex malformations with vaginal septa, an obstructed hemivagina, and hematocolpos (OHVIRA syndrome).

Other Organ Malformations

In addition to urogenital malformations, extrarenal anomalies may occur, particularly cardiovascular, gastrointestinal, musculoskeletal, or central nervous system malformations. In patients with confirmed unilateral renal agenesis, syndromic associations should therefore be considered.

Diagnosis

If a kidney is not visualized on ultrasonography, abdominal MRI is useful to confirm the diagnosis and to identify possible pelvic masses.

Therapy and Follow-up

Long-term follow-up of the congenital solitary kidney is essential and should include ultrasonography, blood pressure monitoring, urine testing for proteinuria, and serial assessments of kidney function. Surgical treatment is required for symptomatic or large pelvic masses.

References

  Deutsche Version: Unilaterale Nierenagenesie

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