Autosomal Recessive Polycystic Kidney Disease Imaging

Introduction:

Autosomal recessive polycystic kidney disease (ARPKD) is a common genetic kidney disease that affects infants and children in the ratio of 1:6,000 to 1:55,000 births. It differs from the autosomal dominant polycystic kidney (ADPKD), which affects older people.

It is characterized by the presence of bilateral, reniform enlargement of the kidneys, which occurs secondary to dilatation of the collecting tubules. Congenital hepatic fibrosis is usually associated with ARPKD, but it remains asymptomatic. Caroli disease (a genetic disorder in which the bile ducts become enlarged) is also associated with ARPKD.

What Are the Symptoms of Autosomal Recessive Polycystic Kidney Disease?

Prenatal Symptoms:

• Oligohydramnios (a condition in which amniotic fluid level is decreased).

• Nephromegaly on fetal ultrasound.

• Defective lung function.

After Birth:

• Nephromegaly (enlarged kidneys) due to cysts.

• Hypertension (abnormally increased blood pressure).

• Growth problems.

• Splenomegaly (enlarged spleen) with decreased red blood cell, platelet, and white blood cell count.

• Breathing problems.

• Polyuria (increased urine production).

• Polydipsia (increased thirst).

• Potters syndrome (lack of amniotic fluid causes deformities of the face, limbs, and ears).

• Portal hypertension (a condition in which the pressure of the portal venous system increases).

• Feeding problems.

• Chronic kidney disease (CKD).

What Are the Guidelines for Imaging Autosomal Recessive Polycystic Kidney Disease?

According to the international working group, there are few guidelines for imaging ARPKD in children. They are-

• Ultrasonography is the most effective imaging tool used to diagnose ARPKD. But additional supporting information such as an ultrasound of the parents, clinical examination, family history, and genetic analysis is required to confirm the diagnosis.

• MRI and MR cholangiopancreatography should be taken in patients with complications of liver disease.

• Annual abdominal ultrasonography is suggested in children with known ARPKD to monitor the signs of portal hypertension.

• In infants with progressive disease, kidney size should be monitored based on their clinical needs.

What Are the Imaging Techniques Used in the Diagnosis of Autosomal Recessive Polycystic Kidney Disease?

Abdominal Radiography:

• The plain abdominal radiography of children in ARPKD shows bilateral flank masses occur due to nephromegaly and centrally displaced bowel (due to the mass).

• Abdominal radiography is insensitive for the diagnosis of renal calcification in ARPKD patients.

• Organomegaly in plain radiography is considered to be a nonspecific finding.

• Plain radiography shows only one-seventh of the renal calcification that appears in computed tomography (CT) scan.

• Perinatal chest radiography shows potter syndrome in severe cases with an elevated diaphragm and hypoplastic thoraces.

• Pneumothorax (collection of air between the lung and the chest wall) or pneumomediastinum are rarely seen in children with ARPKD.

• Splenomegaly (enlarged spleen), hepatomegaly (enlarged liver), and nephromegaly (enlarged kidneys) are seen in older children on plain abdominal radiography.

• Intravenous urograms of neonates show nephromegaly, decreased excretion of contrast material, and dilated collecting tubules.

• The contrast material used in intravenous urogram may remain in the dilated tubules for a few days without excreting into the renal calyces. However, in severe cases, renal excretion is absent.

• Intravenous urography is rarely used in neonates.

• Intravenous urography shows striated nephrogram and rapid excretion in older children. In the excretory urogram during the follow-up, the kidney that was enlarged is seen as small or normal in size.

• The intravenous contrast agent may cause nephrotoxicity in renal failure patients.

• The varices in portal hypertension are confirmed with esophagram.

Computed Tomography (CT) Scan:

• During the perinatal period, a non-enhanced CT scan shows nephromegaly with attenuation values similar to water. Nephromegaly is secondary to dilated, water-containing collecting tubules.

• Striated nephrograms are shown in CT scans after contrast administration. Striated nephrograms are due to the stasis of contrast material in dilated tubules with reduced excretion.

• CT scan is usually not required in young infants. Intrahepatic bile ducts might appear normal or dilated in ARPKD patients on a computed tomography scan.

• In some patients, the renal classification may be bilateral and defuse with moderate to severe kidney failure. Splenomegaly, varices, hepatic duct ectasia may also be seen.

• Intravenous contrast agents cause nephrotoxicity in patients with kidney failure.

Magnetic Resonance Imaging (MRI):

• In fetal MRI, nephromegaly appears as a low signal intensity area on T1 weighted images, and high signal intensity areas on T2 weighted images.

• In ARPKD children, MRI shows nephromegaly with homogenous parenchymal signal without pyelocaliectasis and reniform-shaped kidneys.

• The parenchymal tissues of the kidney show high signal intensity on T2 weighted images, and low signal intensity on T1 weighted images.

• In rapid acquisition with relaxation enhancement (RARE) magnetic resonance urography, hyperintense structures appear radiating in the medulla and cortex, which represents enlarged collecting ducts. In addition, subcapsular renal may also be seen.

• Large maternal size oligohydramnios and unfavorable fetal position are some limiting factors in obstetric MRI.

Ultrasonography:

• Ultrasonography is the first choice of imaging modality in diagnosing autosomal recessive polycystic kidney disease (ARPKD).

• ARPKD appears as enlarged, hyperechoic kidneys on obstetric ultrasound. Newborn ultrasound is performed to evaluate the renal insufficiency or abdominal mass, and in older children, it is used to evaluate portal hypertension.

• Ultrasound with high-frequency transducers can be used in newborns or children that provide high resolution of the resulting images.

• Prenatal ultrasound detects oligohydramnios, enlarged echogenic kidneys, and empty bladder in the severe stage of ARPKD. Sometimes, a fetus with oligohydramnios is associated with abnormal facial appearance, pulmonary insufficiency, and pulmonary hypoplasia.

• Ultrasound elastography of the left liver lobe is an effective biomarker that shows pulmonary hypertension and liver fibrosis in children with ARPKD.

• Ultrasound shows nephromegaly and diffusely echogenic kidneys in neonates affected by autosomal recessive polycystic kidney disease. The echogenicity of kidneys is due to the reflection of the ultrasound waves from dilated collecting tubules or from interstitial edema.

• It is difficult to distinguish the renal cortex from the medulla due to the diffuse echogenic pattern.

• Small or large, discrete lucent cysts are seen in children with autosomal recessive polycystic kidney disease.

Conclusion:

Magnetic resonance imaging is used to visualize the findings of autosomal recessive polycystic kidney disease better than sonography. Magnetic resonance cholangiography is more effective in diagnosing biliary dilatation in ARPKD than ultrasound. However, ultrasound poses fewer advantages, such as lack of sedation, ionizing radiation, and intravenous contrast agents. Doppler ultrasound helps detect blood flow. Renal scintigraphy shows enlarged kidneys with poor renal function in children with ARPKD. Technetium-99m iminodiacetic acid hepatobiliary scintigraphy shows an enlarged left liver lobe, delayed hepatocyte uptake, and delayed excretion of radioactive substances into the biliary tree.