There are some conditions that render the renal parenchyma echogenic on ultrasound examination. While increased renal echogenicity can be a normal variant in children, it has been associated with nephrotic syndrome, glomerulonephritis, and renal dysplasia (Krensky et al., 1983; Brenbridge et al., 1986; Cramer et al., 1986; Kraus et al., 1990). Premature infants also have an increased incidence of increased renal echogenicity (Benacerraf, 1998). While increased echogenicity is a subjective assessment, kidneys that are brighter than liver are considered to be echogenic. This becomes a potential indicator of fetal disease because of the association of this finding with chromosomal abnormality, adult and infantile polycystic kidney disease, Pearlman syndrome, Beckwith–Wiedemann syndrome, and cytomegalovirus infection. The cause of the increased echogenicity of the kidney in these conditions is unknown.

Little data are available to estimate a true incidence of echogenic kidneys in the fetus, in either normal fetuses or those with underlying pathology. However, De La Vega and Torres (2005) in a retrospective review of prenatally diagnosed renal disease found 13 cases among 7714 sonographic studies for an incidence of 0.16% or 1.6 cases per 1000 sonograms (Han et al., 2003).

The kidneys should be considered to be echogenic if the reflectivity of the renal parenchyma is greater than the reflectivity of the liver (Figure 77-1). Once identified, it is important to note other possible associated findings that would aid in the differential diagnosis. It is important to look for other sonographic features that are associated with aneuploidy, especially trisomy 13, including ventriculomegaly, holoprosencephaly, agenesis of the corpus callosum, cleft lip or palate, cyclasia, or microphthalmia. Because of the association of echogenic kidneys with cytomegalovirus infection, attention should be paid to the presence of intracranial calcifications, echogenic bowel, ascites, hydrops, or cardiomegaly (Choong et al., 1993). If the possible renal abnormalities seen with echogenic kidneys (including severe obstructive uropathy at any level from the bladder outlet to the ureteropelvic junction) occur during the second trimester, they can result in increased echogenicity from renal dysplasia. The kidneys in adult and infantile polycystic kidney disease can also be echogenic, but they are usually much larger than normal and may lack normal renal architecture and have severe associated oligohydramnios (see Chapter 79).

As noted above, it is important to remember that increased renal echogenicity is a normal variant and there may be no underlying pathology. The differential diagnosis of echogenic kidneys includes cytomegalovirus infection, aneuploidy, particularly trisomy 13, other chromosomal abnormalities such as partial trisomy 10, adult and infantile forms of polycystic kidney disease, and renal dysplasia secondary to obstructive uropathy (see Table 77-1).