Unilateral multicystic dysplastic kidney (MCDK) has a prevalence of 1 in 4000 births. Contralateral renal abnormalities are present in 30 to 40 percent-most frequently vesicoureteral relux or ureteropelvic junction obstruction (Schreuder, 2009). Nonrenal anomalies have been reported in 25 percent of cases, and cystic dysplasia may occur as a component of many genetic syndromes (Lazebnik, 1999; Schreuder, 2009). If MCDK is isolated and unilateral, the prognosis is generally good.
FIGURE 10-43 Renal agenesis. A.oln this coronal image of the fetal abdomen, color Doppler shows the course of the abdominal aorta. The ultrasound beam is perpendicular to the aorta, demonstrating absence of the renal arteries bilaterally. B. This coronal image of a fetus with unilateral renal agenesis shows the adrenal gland (arrowheads) filling the renal fossa, termed the "lying-down" adrenal sign. The adrenal gland has a hypoechoic cortex and hyperechoic medulla.
FIGURE 10-44 Multicystic dysplastic kidneys. Coronal view of the fetal abdomen demonstrates markedly enlarged kidneys containing multiple cysts of varying sizes that do not communicate with a renal pelvis.
FIGURE 10-45 Posterior urethral valve. In this 19-week fetus with severe bladder outlet obstruction, the bladder is dilated and thickwalled, with dilatation of the proximal urethra that resembles a "keyhole." Adjacent to the bladder is an enlarged kidney with evidence of cystic dysplasia, conferring a poor prognosis.
Bilateral MCDK is found in approximately 1 in 12,000 births. It is associated with severely decreased amnionic luid volume starting early in gestation. his leads to Potter sequence and a poor prognosis (Lazebnik, 1999).
Of the hereditary polycystic diseases, only the infantile form of autosomal recessive poyystic kidney disease (APD) may be reliably diagnosed prenatally. ARPKD is a chronic, progressive disease of the kidneys and liver that results in cystic dilatation of the renal collecting ducts and in congenital hepatic ibrosis (Turkbey, 2009). he carrier frequency of a disease-causing mutation in the PHDI gene approximates 1 in 70, and the disease prevalence is 1 in 20,000 (Zerres, 1998). he phenotypic variability of ARPKD ranges from lethal pulmonary hypoplasia at birth to presentation in late childhood or even adulthood with predominantly hepatic manifestations. Sonographically, infantile ARPKD displays abnormally large kidneys that ill and distend the fetal abdomen and have a solid, ground-glass texture. Severe oligohydramnios confers a poor prognosis.
Autosomal dominant poyystic kidney disease ADPD), which is far more common, usually does not manifest until adulthood (Chap. 53, p. 1031). Even so, some fetuses with AD PKD have mild renal enlargement and enhanced renal echogenicity in the setting of normal amnionic luid volume. he diferential diagnosis for these findings includes several genetic syndromes, aneuploidy, or normal variant.