**3.3. Horseshoe kidney**

Definition: the kidneys are fused in their lower poles, with equal amount of renal tissue bilaterally. The fused portion may be renal parenchyma or fibrous tissue.

Incidence: 1:400.

Pathology: the fusion takes place before the ascent of the kidney which is partially impeded by the emergency of the inferior mesenteric arteries, causing also alteration of the kidneys' axis.

Ultrasound findings: on the standard axial scan, we can see renal tissue in front of the descending aorta. On coronal sections we can see the kidneys fused in the region of the inferior poles (other variants are possible but extremely rare). We also notice a medial rotation of the inferior poles and a lower position than normal kidneys.

Differential diagnosis: includes empty renal fossa (see above), but also severe oligoamnios may suggest pathology due to lack of visibility.

Differential diagnosis: empty renal fossa (see above).

vesicoureteral reflux so postnatal monitoring is recommended.

• Postnatal evaluation of genital organs—uterine anomalies may be associated.

**4. Autosomal recessive polycystic kidney disease (Potter type I)**

microcysts) [3], absent bladder, and oligoamnios (present from 16 weeks).

• Trisomy 13 (holoprosencephaly, polydactyly, facial anomalies).

uation of the spine should be conducted.

aly caused by a gene disorder. Incidence: 1:20,000–1:45,000.

associated with liver fibrosis [4].

fluid and a normal bladder.

Differential diagnosis:

• May be associated with renal anomalies, spina bifida, and sacral agenesis, so attentive eval-

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• As all renal development variants, it may be associated with infections, obstructions, and

Definition: autosomal recessive polycystic kidney disease (ARPKD) is a bilateral renal anom-

Pathology: the PKHD1 gene on chromosome p21 [6] is generally accepted as a primary cause though the specific mechanism is not completely understood. Mutations are specific for individual families. The anomaly is characterized by convoluted tubes and collecting ducts often

Ultrasound findings: ARPKD is characterized by kidney enlargement (>2SD above the mean for that gestational age) [4], increased echogenicity (resulting from the interference of the

• Autosomal dominant polycystic kidney disease (ADPKD)—normal quantity of amniotic

Clinical facts:

**Figure 4.** Horseshoe kidney.

Clinical facts:


#### **3.4. Crossed renal ectopia**

Definition: both kidneys are on the same side of the abdomen; a significant number (95%) are fused.

Incidence: 1:7000.

Ultrasound findings: at the anatomy scan, we notice one empty renal fossa and one abnormally large, frequently bilobed contralateral kidney. Statistically, it is more likely to find the kidney/kidneys on the right side. Color Doppler study shows two renal arteries on the same side (one in the normal position and one lower).

**Figure 4.** Horseshoe kidney.

Differential diagnosis: empty renal fossa (see above).

Clinical facts:

**3.3. Horseshoe kidney**

276 Congenital Anomalies - From the Embryo to the Neonate

Incidence: 1:400.

Clinical facts:

syndrome or trisomy 18.

• Recurrence risk—low in isolated forms.

• Careful anatomy scan to exclude other anomalies.

side (one in the normal position and one lower).

• Prognosis is considered good in isolated forms (**Figure 4**).

digital syndrome).

is recommended.

**3.4. Crossed renal ectopia**

fused.

Incidence: 1:7000.

axis.

Definition: the kidneys are fused in their lower poles, with equal amount of renal tissue bilat-

Pathology: the fusion takes place before the ascent of the kidney which is partially impeded by the emergency of the inferior mesenteric arteries, causing also alteration of the kidneys'

Ultrasound findings: on the standard axial scan, we can see renal tissue in front of the descending aorta. On coronal sections we can see the kidneys fused in the region of the inferior poles (other variants are possible but extremely rare). We also notice a medial rotation of the inferior

Differential diagnosis: includes empty renal fossa (see above), but also severe oligoamnios

• Risk of chromosomal anomalies—horseshoe kidney may be found in fetuses with Turner's

• Risk of nonchromosomal syndrome (caudal regression syndrome, otocephaly, Oro-facial

• Karyotyping should be offered (especially if other anomalies or soft markers are present). • Postnatal monitoring for vesicoureteral reflux, hydronephrosis, and urinary tract infections

Definition: both kidneys are on the same side of the abdomen; a significant number (95%) are

Ultrasound findings: at the anatomy scan, we notice one empty renal fossa and one abnormally large, frequently bilobed contralateral kidney. Statistically, it is more likely to find the kidney/kidneys on the right side. Color Doppler study shows two renal arteries on the same

erally. The fused portion may be renal parenchyma or fibrous tissue.

• It is frequently associated with hydronephrosis and genital anomalies.

• 33% of cases have CNS and cardiac or skeletal malformations [5].

poles and a lower position than normal kidneys.

may suggest pathology due to lack of visibility.

