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1
Question:

A newborn undergoes an abdominal ultrasound that shows kidneys of normal size, structure, and location.  The patient does not appear to be in distress, and physical examination reveals no abnormalities.  If this patient were to be diagnosed with renal disease later in life, it would most likely be which of the following?

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Explanation:

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Autosomal dominant polycystic kidney disease

Pathologic features

  • Mutations in PKD-1 or PKD-2 cause tubular cell proliferation & fluid secretion
  • Cyst formation occurs at any point in the nephron, but <5% of nephrons are affected
  • Microscopic cysts present at birth progressively enlarge over the decades
  • Enlarged cysts compress the renal parenchyma, causing atrophy & fibrosis

Clinical features

  • Frequently clinically silent, with 50% of patients going undiagnosed
  • Symptoms are variable & include flank pain, hematuria & hypertension
  • Renal failure slowly progresses over 10-20 years, with end-stage renal disease often occurring by age 70
  • Extrarenal manifestations include liver cysts & cerebral aneurysms

Autosomal dominant polycystic kidney disease (ADPKD), like many autosomal dominant diseases, manifests later in life (eg, age 40-50).  Microscopic cysts are present at birth but are too small to be detected by abdominal ultrasound.  Over the years, the cysts enlarge, compression of the renal parenchyma occurs, and patients become symptomatic (eg, flank pain, hypertension).

In contrast, autosomal recessive polycystic kidney disease (ARPKD) presents at birth or during the first year of life with bilateral flank masses.  Cysts are formed by dilated distal tubules and collecting ducts.  Abdominal ultrasonography demonstrates enlarged kidneys at birth and often shows cysts, which are visualized if they are >1 cm in diameter (Choice B).

(Choice C)  The abnormal fusion of kidneys at their poles (usually the lower poles) is called horseshoe kidney.  The isthmus of renal tissue is anterior to the great vessels and is easily detected on abdominal ultrasound.

(Choice D)  Multicystic dysplastic kidney is characterized by the presence of multiple renal cysts of varying sizes and the absence of a normal pelvicalyceal system.  The condition is associated with ureteral or ureteropelvic atresia, with the affected kidney essentially rendered nonfunctional.  Abdominal ultrasound of the fetus or newborn is typically diagnostic.

(Choice E)  A number of fetal renal abnormalities (eg, bilateral renal agenesis, ARPKD) can cause a decrease in fetal urine production and oligohydramnios.  The combination of abnormalities that ensues, called Potter sequence, includes pulmonary hypoplasia, Potter facies (flattened nose, recessed chin, prominent epicanthal folds, and low-set ears), limb deformities, and cardiovascular abnormalities.  Renal defects that lead to Potter sequence are usually profound and easily seen on ultrasound.

Educational objective:
Autosomal dominant polycystic kidney disease typically manifests in patients age 40-50 with enlarged kidneys, flank pain, and hypertension.  In newborns, the kidneys are of normal size, and the cysts are too small to be detected on abdominal ultrasonography.  As the cysts enlarge, they compress the renal parenchyma and cause symptoms.