**3.1. Unilateral agenesis**

Definition: one kidney does not form resulting one present kidney and one renal artery.

Incidence: 1:1000 [2].

Pathology: failure of development of only one ureteric bud with normal development on the other side.

**3.2. Pelvic kidney**

Incidence: 1:700–1:1200 [2–4].

happens between 6 and 10 weeks of gestational age.

kidney can have vascularization from the iliac arteries.

Differential diagnosis: empty renal fossa (see above).

• May be a family group so parents should be scanned.

• Pelvic kidney should be the first thing to search in an empty renal fossa.

• May be associated with genital, gastrointestinal, or cardiac anomalies.

• Visualization can sometimes be difficult due to bowel loops or interposed iliac wing.

• Risk of chromosomal anomalies is low and so is the risk of nonchromosomal syndromes.

• Vesicoureteral reflux is frequently present so postnatal ultrasound monitoring is recom-

kidney.

Clinical facts:

mended (**Figure 3**).

**Figure 3.** Pelvic kidney.

Definition: the presence of one kidney in the pelvis; the most common location for ectopic

Renal Anomalies

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Pathology: the kidney forms normally but fails to ascend to the lumbar area. This normally

Ultrasound findings: the first thing we notice is an empty renal fossa; careful scanning reveals the kidney adjacent to the bladder. The normally positioned kidney shows no compensatory hypertrophy. Amniotic fluid is within a normal range. The use of color Doppler can be helpful—sometimes, you can follow the renal artery to the ectopic kidney, but sometimes a pelvic

Ultrasound findings: we notice an empty renal fossa on axial view; this view should be completed with longitudinal and coronal views. The contralateral kidney is increased in size (>95 percentile)—compensatory hypertrophy. The use of color Doppler shows only one renal artery. Some structures may mimic the second kidney—one is the adrenal gland, and the other is the colon.

Differential diagnosis: an empty renal fossa may be present in:


Clinical facts:


**Figure 2.** Unilateral renal agenesis.
