Imaging in Autosomal Recessive Polycystic Kidney Disease

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Autosomal recessive polycystic kidney disease (ARPKD) is the most common heritable cystic renal disease occurring in infancy and childhood. It is distinct from autosomal dominant polycystic kidney disease (ADPKD), which tends to occur in an older population. The clinical spectrum shows a wide variability, ranging from perinatal death to a milder progressive form, which may not be diagnosed until adolescence. ^{[1, 2]} See the images below.

Ultrasonography is the primary radiographic modality for the evaluation of autosomal recessive polycystic kidney disease (ARPKD), especially during the perinatal and neonatal periods. ^[3] Intravenous urography is less commonly used to evaluate the kidneys. In older children, CT and MRI are often used to evaluate liver disease. ^{[4, 5]}

In the neonate, plain abdominal radiographs may demonstrate bilateral flank masses due to nephromegaly; these masses may cause the bowel to become displaced centrally (see the image below).

In severe cases, perinatal chest radiographs show Potter syndrome with hypoplastic thoraces and an elevated diaphragm. Occasionally, pneumothoraces or pneumomediastinum is observed. In the older child, hepatomegaly, splenomegaly, and nephromegaly are seen on plain abdominal radiographs.

In the neonate, intravenous urograms reveal decreased excretion of contrast material, nephromegaly, and characteristic striated nephrograms due to dilated collecting tubules (see the image below). Contrast material may remain in the dilated tubules for days without visible excretion into the renal calyces. In more severe cases, renal excretion may be absent. Intravenous urography is rarely used in the very young infant.

In the older child, intravenous urography demonstrates more rapid excretion and a striated nephrogram. On follow-up excretory urograms, kidneys that were initially enlarged are seen to be smaller or even of normal size. One should remember that intravenous contrast material is nephrotoxic in patients with renal failure.

Esophagraphic results can confirm the presence of varices in patients with portal hypertension.

The demonstration of organomegaly on plain images is a nonspecific finding. Plain radiographs are also insensitive for the detection of renal calcification in patients with ARPKD.

In one study of patients with ARPKD, plain radiographs demonstrated only one seventh of the renal calcifications that were demonstrated on CT scans. Occasionally, renal function in neonates is so poor that their kidneys cannot be visualized with intravenous urography.

In the perinatal period, nonenhanced CT scans demonstrate nephromegaly with renal attenuation values approximating that of water. This feature is secondary to the water-containing, dilated, collecting tubules (see the image below). After the administration of contrast material, striated nephrograms are observed; these are due to the stasis of contrast medium in dilated tubules with diminished excretion.

In one study, 7 of 9 children aged 9-15 years had had CT scans that demonstrated renal calcifications. These calcifications were always bilateral and diffuse but tended to be more significant in ARPKD patients with moderate to severe renal failure.

CT examination may also demonstrate hepatic duct ectasia, varices, and splenomegaly.

One should remember that intravenous contrast material is nephrotoxic in patients with renal failure.

CT is generally not required in the very young infant. Intrahepatic bile ducts may appear either dilated or normal on CT examinations of patients with ARPKD.

MRI may be used to characterize the findings of autosomal recessive polycystic kidney disease (ARPKD) in utero, possibly with better detail than sonography. Fetal MRI demonstrates nephromegaly with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. This finding is attributed to the fluid-filled, ectatic collecting ducts.

Renal MRIs of children with ARPKD may demonstrate nephromegaly with reniform-shaped kidneys and a homogeneous parenchymal signal pattern without pyelocaliectasis. The renal parenchyma has high signal intensity with T2-weighted sequences and usually has low signal intensity with T1-weighted sequences. In rapid acquisition with relaxation enhancement (RARE) magnetic resonance urography, hyperintense linear structures are seen radiating in the cortex and medulla. They represent dilated collecting ducts. Small subcapsular renal cysts may be seen. In a series of 8 children with ARPKD, MRIs failed to demonstrate hepatic fibrosis or bile duct dilatation. ^{[6, 7, 8, 9, 10, 11]}

An unfavorable fetal position, a large maternal size, and oligohydramnios are some of the factors that can limit obstetric MRI.

Magnetic resonance cholangiography is more sensitive than sonography in the detection of biliary dilatation in children with ARPKD.

Ultrasonography is often the first imaging modality used to diagnose cases of autosomal recessive polycystic kidney disease (ARPKD). The diagnosis may be suspected because of enlarged, echogenic kidneys on an obstetric sonogram, on a newborn’s sonogram obtained to evaluate abdominal masses or renal insufficiency, or on an older child’s sonogram obtained to evaluate portal hypertension.

The small size of a newborn or child facilitates the use of high-frequency ultrasound transducers that have outstanding resolution. The ability to perform imaging studies without the risk of sedation, intravenous contrast material, or ionizing radiation is an advantage of sonography. Images can be obtained in a number of planes to facilitate interpretation. In some circumstances, Doppler ultrasonography is used to evaluate blood flow.

Prenatal sonography may demonstrate echogenic, enlarged kidneys, oligohydramnios, or an empty urinary bladder in severe cases of ARPKD; however, these findings are not demonstrable in all cases (see the images below). Severely affected fetuses with oligohydramnios often have pulmonary hypoplasia, abnormal facies, and high mortality due to pulmonary insufficiency (Potter syndrome).

In the neonate with ARPKD, sonograms usually show symmetric nephromegaly without contour-deforming masses (see the images below). There may be fetal lobation, which is a normal finding. The kidneys are often diffusely echogenic. This has been attributed to reflection of the ultrasound waves from the many acoustic interfaces of dilated medullary collecting ducts, or perhaps to increased acoustic interfaces from interstitial edema. Frequently, there is loss of the differences in echogenicity that distinguishes the renal cortex from the renal medulla).

In less severe cases, a sonolucent rim of cortical tissue may be present. This rim has variously been attributed to compressed cortical tissue without duct ectasia, to perirenal fluid, and to elongated thin wall cysts in the peripheral cortex (see the image below).

Discrete, small sonolucent cysts and, less frequently, larger cysts may occasionally be seen on sonograms of patients with ARPKD (see the images below).

These cysts are more likely to be demonstrated with modern high-resolution equipment (see the image below). A rare but interesting case was reported in which the sonogram demonstrated focal sonolucent macrocysts that contained radiating septations. These corresponded pathologically to radially oriented, dilated collecting tubules.

In premature infants with severe ARPKD, the increased echogenicity may be localized to the pyramids, mimicking medullary nephrocalcinosis (see the images below). Because liver involvement tends to be less severe in newborns, the livers of newborns with ARPKD usually appear normal on ultrasonography; however, increased hepatic echogenicity or early bile duct ectasia on sonography has been reported. Long-term imaging demonstrates the emergence of hepatic fibrosis and portal hypertension and has been reported to show the development of splenomegaly, often with varices.

In children and neonates, renal sonography may show increased echogenicity in the kidneys, particularly in the pyramids, loss of corticomedullary junction differentiation, mild to moderate nephromegaly, and (occasionally) dilated cystic-appearing collecting ducts. There are some published data regarding the patterns of serial renal growth and the changing patterns of renal echogenicity in children with ARPKD. One study of long-term survivors reported that renal size tends to peak at 1-2 years of age and then decreases until age 4-5 years, with the echogenicity returning to normal. Another group found little change in the nephromegaly over time and that diffuse hyperechoic foci correlated with the onset of renal failure. Renal calculi may be seen with sonography. Microcalcification in ARPKD is caused by the precipitation of calcium within dilated collecting ducts. This is attributed to decreased urinary citrate excretion and abnormally alkaline urine.

Patients presenting in childhood often have portal hypertension. Long-term survivors with ARPKD develop portal hypertension secondary to hepatic fibrosis. The sonogram may show hepatosplenomegaly, echogenic livers, and ectatic bile ducts that contain nodular protrusions or bridge formation across the ductal lumen (see the images). Increased through-transmission of the ultrasound beam is seen beyond the dilated bile-filled ducts. Choledocholithiasis and complicating cholangitis may develop.

Sonography of patients with portal hypertension may reveal collateral veins, and Doppler sonography demonstrates the velocity and direction of blood flow within the portal vein. Color-flow Doppler provides qualitative information, and duplex Doppler provides quantitative information about portal venous flow. Rarely, areas of intrahepatic duct ectasia with a central echogenic do may be seen in tpatients with ARPKD; such findings are characteristic of Caroli disease. Caroli disease has been associated with ARPKD. ^{[9, 12, 13, 14, 15, 16, 17, 18, 19, 20]}

Ultrasonography is highly operator dependent, and its utility often depends on the skill of the person performing the study and not just the individual interpreting the final images.

On renal sonography, small foci of intense echogenicity, with or without acoustic shadowing, have been attributed to either microcalcifications or reflections from the walls of multiple tiny cysts (see the image below). Renal calcifications occur in ARPKD but are more frequently seen with CT than sonography.

In utero, autosomal recessive polycystic kidney disease (ARPKD) is usually not diagnosed with obstetric sonography before the second half of pregnancy; however, ARPKD is uncommonly suspected on the basis of sonographic results during the early second trimester.

Autosomal dominant polycystic kidney disease (ADPKD) and glomerulocystic kidney disease can present in newborns with bilaterally enlarged echogenic kidneys that are indistinguishable from ARPKD. In these cases, the family history may suggest ARPKD. In approximately 10% of ADPKD cases, there is asymmetric renal involvement; is is very uncommon in ARPKD. Other conditions that have echogenic nephromegaly include bilateral renal vein thrombosis, congenital nephrotic syndrome, and diffuse cystic renal dysplasia that are seen in syndromes such as Meckel syndrome, Goldston syndrome, Zellweger syndrome, and Jeune syndrome.

Obstetric ultrasonographic findings in ARPKD are not always demonstrable in the second trimester of pregnancy.

Sonographic examinations are highly operator dependent, and the findings, when demonstrated, may be nonspecific.

In the newborn with severe autosomal recessive polycystic kidney disease (ARPKD) involvement, renal scintigraphy shows enlarged reniform kidneys with poor function. In older children, hepatobiliary scintigraphy can demonstrate cholestasis and intrahepatic duct dilatation. Technetium-99m (^99m Tc) iminodiacetic acid (HIDA) hepatobiliary scintigraphy may demonstrate enlargement of the left lobe of the liver; delay in maximal hepatocyte uptake; delayed excretion of radionuclide into the biliary tree, which is often dilated; and delayed excretion into the bowel. ^{[19, 21, 22]}

Technetium-99m DMSA renal scintigraphic findings are not specific and are variable. Reported patterns include both nonspecific discordant focal defects throughout the kidneys, particularly at the poles, and homogeneous renal uptake. In very young infants renal^99m Tc mercaptoacetyltriglycine (MAG3) may show enlarged poorly functioning kidneys, even when the kidneys cannot be demonstrated by excretory urography.

In a small minority of patients with ARPKD, results of renal or hepatobiliary nuclear medicine imaging studies are normal.

Angiography is not usually required for patients with autosomal recessive polycystic kidney disease.

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Ben Y Young, MD Clinical Assistant Instructor, Staff Physician, Department of Radiology, Stony Brook University Hospital

Ben Y Young, MD is a member of the following medical societies: American College of Radiology

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

Eugene C Lin, MD Attending Radiologist, Teaching Coordinator for Cardiac Imaging, Radiology Residency Program, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine

Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, Society of Nuclear Medicine and Molecular Imaging

Disclosure: Nothing to disclose.

John L Haddad, MD Clinical Associate Professor, Department of Radiology, Weill Medical College of Cornell University; Director of Body MRI, Department of Radiology, Methodist Hospital in Houston

John L Haddad, MD is a member of the following medical societies: American College of Radiology, American Medical Association, and Radiological Society of North America

Disclosure: Nothing to disclose.

Steven Perlmutter, MD, FACR Associate Professor of Clinical Radiology, The School of Medicine at Stony Brook University; Medical Director of Radiology, Peconic Bay Medical Center

Steven Perlmutter, MD, FACR is a member of the following medical societies: American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Association of Program Directors in Radiology, Association of University Radiologists, Medical Society of the State of New York, Radiological Society of North America, Society of Breast Imaging, Society of Nuclear Medicine, andSociety of Uroradiology

Disclosure: Nothing to disclose.

Thomas H Smith, MD Associate Professor, Departments of Radiology and Pediatrics, The School of Medicine at Stony Brook University

Disclosure: Nothing to disclose.

Imaging in Autosomal Recessive Polycystic Kidney Disease

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