Genito-urinary Imaging
Figure 5: Potter Type II (Multicystic Dysplastic Kidney Disease) AB C
A: Unilateral medullary cystic kidney disease. Scan at 33 weeks of gestation shows left fetal kidney replaced by multiple cysts of varying size; B: Normal right fetal kidney in the same patient; C: Post-natal scan confirming the pre-natal findings involving the left kidney.
Multicystic dysplastic kidney is the most common type of renal dysplasia, is usually sporadic, and has an incidence of one in 10,000 for bilateral disease, with a male to female ratio of 2:1. It is common in the infants of women with diabetes. There is an association with Meckel-Gruber and Apert syndromes.4
Different classifications exist, including: unilateral (pelvoinfundibular atresia) or bilateral (urethral atresia or severe bladder outlet obstruction); Potter’s IIa (large kidney with multiple cysts due to ureteropelvic junction obstruction) or Potter’s IIb (small echogenic or normal-size kidney related to distal ureter or urethral obstruction); and hydronephrotic or non-hydronephrotic. In the latter, the hydronephrotic classification has a large central cyst (dilated pelvis) with additional communicating cysts and a late onset (beyond the 10th week of gestation), while the non-hydronephrotic classification has an atretic/small renal pelvis, and calyces and cysts with loss of reniform structure, and an early onset (eight to 10 weeks of gestation).
Unilateral, bilateral, and segmental forms have been described. The unilateral form of MCKD is the most common, seen in 80–90 % of cases.4
of cases,4
horseshoe kidney (5–9 %), ureteral anomalies (5 %), and renal hypoplasia/agenesis (11 %).6
The unilateral form has been reported with
cardiovascular, gastrointestinal, and central nervous system anomalies, as well as with diaphragmatic hernia. Bilateral MCKD is seen in 20 % of cases and is often associated with oligohydramnios and pulmonary hypoplasia. Bilateral MCKD or unilateral MCKD with contralateral renal agenesis are uniformly fatal.6 focal infundibulum obstruction.
The segmental form of MCKD is caused by
On imaging of MCKD, a cystic mass resembling a cluster of grapes can be seen in the lumbar region (see Figure 5). Cystic changes are usually not visible until after 20 weeks of gestation.4
Potter Type III
Potter type III corresponds to autosomal dominant (or adult-type) PKD,6 the most common form of PKD, which ultimately results in end-stage renal insufficiency. It is not commonly diagnosed on pre-natal sonography, although it is probably already present at birth.6 collecting tubules and nephrons intermix with abnormal tissue.6
Normal There is
bilateral asymmetric renal enlargement with associated nodular renal contours on sonography.6 may appear normal.6
Prior to 20 weeks of gestation, the kidneys
Repeat sonography in the third trimester may show enlarged kidneys, enlarged echogenic kidneys, or multiple renal cysts.6
Potter Type IV
Potter type IV corresponds to cystic renal dysplasia resulting from urethral obstruction; alternatively, it can occur secondary to ureteropelvic or ureterovesical obstruction owing to elevated urinary tract pressures.6
The severity of disease correlates with the degree and duration of obstruction. Renal dysplasia with urinoma, ascites, and oligohydramnios indicate poor prognosis.3
It is associated with contralateral renal anomalies in 20–50 % including ureteropelvic junction obstruction (7–27 %),
are sonographically evident and they may appear normal on screening examination.4
If detected on imaging, there is typically increased renal parenchymal echogenicity and renal cortical cysts in the presence of obstructive uropathy.6
A dilated thick-walled urinary bladder may help
differentiate Potter type IV cystic renal disease from Potter type II.6 Overall, the degree of pathology correlates with the timing and severity of obstruction. If early and complete obstruction occurs, the pathology simulates that seen in Potter types II or III renal cystic disease. If late or mild obstruction occurs, sonography may reveal pelvicaliceal system dilatation without cystic changes.6
Conclusion No normal renal
parenchyma or reniform shape is seen. In bilateral MCKD, there may be marked oligohydramnios and lack of visualization of the bladder on prolonged examination.
1. Mandell J, Blyth BR, Peters CA, et al., Structural genitourinary defects detected in utero, Radiology, 1991;178:193–6.
2. Anderson N, Boswell O, Duff G, Prenatal sonography for the detection of fetal anomalies: results of a prospective study and comparison with prior series, AJR Am J Roentgenol, 1995;165:943–50.
Fetal genito-urinary abnormalities can be detected in utero. Pre-natal sonography can be especially useful when such abnormalities are not otherwise suspected. Detection of anomalies aids in management and intervention decisions. Detection of more than one fetal anomaly may prompt early amniocentesis.2
Appropriate actions can then be taken to improve survival or reduce morbidity. n
3. Zhou Q, Cardoza JD, Barth R, Prenatal sonography of congenital renal malformations, AJR Am J Roentgenol, 1999;173:1371–6.
4. Rouse GA, Kaminsky CK, Saaty HP, Current concepts in sonographic diagnosis of fetal renal disease, RadioGraphics, 1988;8:119–32.
5. Arger PH, Coleman BG, Mintz MC, et al., Routine fetal genitourinary tract screening, Radiology, 1985;156:485–9.
6. Fong KW, Rahmani MR, Rose TH, et al., Fetal renal cystic disease: sonographic–pathologic correlation, AJR Am J Roentgenol, 1986;146:767–73.
Not all dysplastic kidneys
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