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KEY POINTS
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Key Points

  • Developmental anomaly that occurs at 4 to 6 weeks of embryonic life.

  • Incidence of bilateral renal agenesis is 1 in 3000 livebirths;for unilateral renal agenesis it is 1 in 500–1300 livebirths and higher in twins.

  • Sonographic findings are severe oligohydramnios or anhydramnios occurring after 14 to 16 weeks in bilateral renal agenesis. In unilateral cases, the remaining kidney may be >95% in length for gestational age.

  • Syndromes associated with bilateral renal agenesis are sirenomelia, caudal regression, branchio-oto-renal, cerebro-oculo-facial, Fraser, and Rokitansky–Kuster–Hauser. DiGeorge syndrome is also associated with unilateral renal agenesis.

  • Consider amnioinfusion to obtain a karyotype.

  • Most hereditary cases are inherited as an autosomal dominant condition with variable expressivity.

  • Sonographic screening of the parental kidneys is recommended.

  • Outcome is uniformly fatal for bilateral renal agenesis.

  • For unilateral renal agenesis consider postnatal radionucleide scan, voiding cystourethrography, and prophylactic antibiotics.

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CONDITION
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Renal agenesis is the congenital absence of one or both kidneys as a result of the complete failure of the kidney to form. The sequence of renalagenesis, severe oligohydramnios, amnion nodosum, flattened face, low set and floppy ears, bilateral pulmonary hypoplasia, and perinatal death was first described by Potter in 1946.

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Renal agenesis is a developmental anomaly that occurs at 4 to 6 weeks of embryonic life (Kaffe et al., 1977). Normal renal embryogenesis requires that three events take place: the ureteric buds must arise bilaterally from mesonephric (wolffian) ducts; subsequently, bilateral metanephric blastema must form from mesoderm in the caudal region of the nephrogenic cord; and finally, ureteric buds must grow, contact, and invaginate the metanephric blastema, there by inducing differentiation of the blastema into two mature kidneys (Wax et al., 1994). Failure of the metanephros to develop results in complete absence of the kidney. This can be due to either nonexistence of the ureteral bud or failure of the ureteral bud to develop from the wolffian duct.

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In unilateral renal agenesis, there is complete absence of the kidney on one side, with compensatory hypertrophy on the contralateral side. Most cases of unilateral renal agenesis are due to lack of induction of the metanephric blastema by the ureteral bud, but some cases of absent kidney may be due to in utero regression of a multicystic dysplastic kidney (see Chapter 78) (Mesrobian et al., 1993). In cases of unilateral renal agenesis, compensatory hypertrophy of the remaining kidney occurs prenatally (Zalel et al., 2002). This has been demonstrated by Hartshorne et al. (1991), who performed a retrospective analysis of 20 fetuses who died with unilateral renal agenesis. Total renal mass was measured and was shown to comprise 82.7% of the weight of both kidneys removed from control fetuses at the same gestational age. Had prenatal compensatory hypertrophy not occurred, the total renal masswould have been only 50% of control values (Hartshorne et al., 1991). It is ...

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