Imaging in Autosomal Dominant Polycystic Kidney Disease
- Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD more...
Adult polycystic kidney disease, which affects approximately 1 in 1000 people, is transmitted as an autosomal dominant trait. Cysts arise from the nephrons and collecting tubules; microdissection reveals that the cysts communicate directly with the nephrons and collecting tubules. Islands of normal parenchymal renal tissue are interspaced between the cysts. For examples of polycystic kidney disease, see the images below.
Patients present with hypertension and progressive renal failure after their third decade of life. Autosomal dominant polycystic kidney disease (ADPKD) is uncommon in children and is rarely seen in neonates.
Between 29% and 73% of patients with the disorder have associated hepatic cysts, 9% have associated pancreatic cysts, and 5% have associated splenic cysts; pulmonary cysts occur but are uncommon. These extrarenal manifestations are not found in neonates and children.[1, 2, 3, 4, 5, 6, 7, 8]
Gardner and Evan showed that individuals older than age 40 years with a family history of ADPKD but without renal cysts are unlikely to develop the disease. Others have shown that when screening for evidence of ADPKD, if the kidney shows no signs of cysts or parenchymal abnormality in a patient by age 19 years, that individual is extremely unlikely to be affected.
Ultrasonography is the procedure of choice in the workup of patients with ADPKD, and it is an ideal modality for screening patients' families (see the images below). Plain radiographs offer limited information. Plain radiographic findings are normal in the early stages of ADPKD, but with enlargement of the kidneys, soft-tissue masses displace the intra-abdominal organs.
In studies in young children, intravenous urography and nephrotomography were shown to be slightly more sensitive than ultrasonography.
Computed tomography (CT) scanning is as sensitive as ultrasonography in the detection of cystic disease, although problems may arise with smaller cysts. CT scanning appears to be more specific than ultrasonography in differentiating an obstructed renal pelvis from a parapelvic cyst. It also seems to be superior to ultrasonographic images in helping to assess retroperitoneal rupture of a cyst and perinephric extension of blood or pus from an infected cyst.[9, 10] Magnetic resonance imaging (MRI) is especially useful for examining patients who are allergic to iodinated contrast media and those with compromised renal function who are at risk for iodinated contrast–induced renal failure. MRI also has advantages for patients in whom hemorrhagic cysts are considered and is probably superior to other modalities in characterizing complicated cysts.[11, 12, 13, 14]
Radionuclide studies have a complementary role in the assessment of renal function in ADPKD. These studies do not have the added hazard of patient exposure to iodinated contrast material.
Limitations of techniques
Nephromegaly, which can be detected on plain radiographs, may result from causes other than ADPKD. Similarly, curvilinear calcification is not specific for ADPKD and may be found in other types of cysts, as well as in tumors and granulomas. Simple renal cysts with nongenetic origins may be similar to ADPKD lesions. Also, cysts associated with ADPKD cannot always be differentiated from multiple simple cysts and cysts associated with von Hippel–Lindau disease or tuberous sclerosis. Such findings apply to intravenous urography (seen in the image below), ultrasonography, CT scanning, MRI, and angiography.
The role of angiography in the diagnosis of ADPKD is limited. Although angiography has a high degree of accuracy in diagnosing ADPKD, its specificity is low.
Plain radiographic findings are normal in the early stages of autosomal dominant polycystic kidney disease (ADPKD); however, with enlargement of the kidneys, soft-tissue masses that displace intra-abdominal organs may be seen.
Renal enlargement is often asymmetrical, and usually, normal renal outlines cannot be traced.
Cysts may calcify in a curvilinear, ringlike, or amorphous manner, as seen in the image below. The presence of renal calculi may signify urinary tract infection.
In younger, asymptomatic patients, the kidneys may be smoothly enlarged, with normal collecting systems depicted by intravenous urography; eventually, however, the renal contour becomes lobulated.
Nephrogram findings may have a characteristic Swiss cheese appearance resulting from numerous, smoothly marginated radiolucencies distributed throughout the renal cortex and medulla.
The pelvocaliceal systems demonstrate bilateral, diffuse irregularity and splaying. The collecting system may be elongated, distorted, and attenuated. These changes are seen in the image below.
Large cysts may occasionally obstruct a calyx.
Occasionally, cysts may rupture into the collecting system and appear, on intravenous urography or retrograde pyelography, as a contrast material–filled cavity communicating with a calyx.
In ADPKD, the kidneys shrink with the onset of renal failure, after renal transplantation, or as a result of long-term hemodialysis.
Uncommonly, patients with well-developed renal cysts, even patients with chronic renal failure, have normal-sized kidneys.
Delayed, diffuse, nodular puddling of contrast material throughout the renal parenchyma has been reported in neonates with ADPKD. This phenomenon is said to be useful in differentiating ADPKD from autosomal recessive polycystic kidney disease (ARPKD). In ARPKD, the nephrogram usually shows striation, with persistent radiating opaque streaks on delayed images (sunburst nephrogram).
Retrograde pyelography may demonstrate normal findings when the cysts are small. With larger cysts, this modality may reveal splaying, effacement, and, uncommonly, dilatation of the calyces and the renal pelvis. Some cysts may fill with contrast material.
Degree of confidence
Plain abdominal radiographs have low specificity and generally are not recommended in the workup of patients with ADPKD.
Differentiating between multiple simple renal cysts and the cysts of ADPKD may be difficult with intravenous urography.
Detectable on plain radiographs, nephromegaly may result from causes other than ADPKD. Similarly, curvilinear calcification may occur in simple renal cysts and tumors. Simple renal cysts with nongenetic origins can resemble ADPKD cysts, as can lesions arising from von Hippel–Lindau disease or tuberous sclerosis.
On CT scans, the cysts in autosomal dominant polycystic kidney disease (ADPKD) are fairly well-defined, round or oval masses with low attenuation values similar to those of water (see the images below).
After the intravenous administration of iodinated contrast material, cysts do not enhance but instead stand out prominently against normally enhancing background renal tissue.
Obstruction of a calyx or, rarely, the renal pelvis may occur. In the early disease stages, renal size may be normal and the reniform shape of the kidneys is well maintained.
With advancing disease, the size and number of cysts increase and the renal outline may become scalloped, with the cyst projecting beyond the renal outline.
With end-stage renal disease, unenhanced CT scans may depict curvilinear or amorphous calcification within the walls of the cyst. Renal calculi are well depicted on CT scans.
Acute hemorrhage into a cyst is shown as a high-attenuation mass on unenhanced scans in patients presenting with acute flank pain. These hemorrhagic cysts are usually subcapsular. With time, the hemorrhage resolves and the attenuation of the cystic contents is reduced.
Spontaneous hemorrhage into the retroperitoneum is a known complication that is demonstrated readily on CT scans.
Infected cysts usually have thick, irregular walls that often calcify. The attenuation value of an infected cyst is slightly higher than that of water; the value may vary within the cyst because of the presence of debris.
Localized thickening of the Gerota fascia may be associated with cyst infection and renal abscess.
Degree of confidence
CT scanning is a sensitive modality for examining cystic kidney disease. However, problems may arise with smaller cysts, which may not be easily differentiated from small, solid masses. Occasionally, differentiation of chronically infected cysts from a necrotic tumor also may be difficult.
CT scanning appears to be more specific than ultrasonography in differentiating an obstructed renal pelvis from a parapelvic cyst on the basis of contrast excretion pattern. It is also useful in helping assess retroperitoneal rupture of a cyst and perinephric extension of blood or pus from an infected cyst.
As with images derived from intravenous urography, CT scans of lesions associated with ADPKD can resemble CT scans of simple renal cysts of nongenetic etiology, as well as CT scans of cysts associated with either von Hippel–Lindau disease or tuberous sclerosis.
Magnetic Resonance Imaging
Renal cysts show a homogeneous, low to intermediate signal intensity on T1-weighted images and a homogeneous, high signal intensity on T2-weighted images.
Cysts have thin, imperceptible walls. Renal cysts do not enhance with gadolinium-based contrast material.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.
As they do when imaged in other modalities, kidneys affected by autosomal dominant polycystic kidney disease (ADPKD) appear large on MRI scans and have irregular, distorted contours.
Uncomplicated cysts resemble simple cysts.
MRI can be used to help characterize renal cysts that are equivocal with other imaging modalities; such cysts include hyperintense cysts, hemorrhagic cysts, and cysts with calcification or septa.
Cysts complicated by hemorrhage may look hyperintense on all image sequences, but appearances may depend on the age of the hemorrhage.
Layering may be present with a recent intracystic bleed.
Cysts complicated by infection or those with high protein content may present with an intermediate signal intensity on T1-weighted or T2-weighted images.[12, 13, 14]
Degree of confidence
MRI of the kidneys is becoming a useful technique for characterization of renal masses and can be used in addition to or instead of CT scanning. MRI is especially useful in patients who are allergic to iodinated contrast media and in those with compromised renal function who are at risk for iodinated contrast–induced renal failure. MRI has the added advantage of multiplanar imaging and does not require the use of ionizing radiation. Moreover, MRI is probably superior to other modalities in characterizing complicated cysts.
As with images derived from intravenous urography and CT scanning, MRI scans of simple renal cysts of nongenetic etiology, as well as those of cysts associated with either von Hippel–Lindau disease or tuberous sclerosis, can resemble scans of lesions associated with ADPKD.
Ultrasonography is a valuable screening test for patients in whom polycystic disease is suspected (see the image below).[16, 17]
Most children with autosomal dominant polycystic kidney disease (ADPKD) have normal ultrasonographic findings at birth.
In neonates who are severely affected, the kidneys are large and echogenic, with loss of corticomedullary differentiation indistinguishable from that of ARPKD.
When cysts are seen, they vary in size (as seen in the images below) and are scattered throughout the cortex, including in medullar and subcapsular locations. By contrast, the peripheral cortex is spared in patients with mild ARPKD.
Sequential examinations usually demonstrate an increase in cyst size and number over a period of years, resulting in calyceal distortion and irregularity of the renal outline.
Cysts may have irregular walls and may show internal echoes if complications of hemorrhage or infection are present.
Surviving islands of renal parenchyma may be seen between cysts. Calcification of cyst walls may be seen later in life.
Cysts of the liver, pancreas, and spleen may help to confirm the diagnosis of ADPKD (see the images below).
ADPKD is a rare occurrence in the fetus. The kidneys may be enlarged as a result of cystic dilatation of tubules and glomeruli, and this is associated with increased echogenicity mimicking autosomal recessive disease. Occasionally, the cortical cysts are large enough to be detected on ultrasonographic images; this can confirm the diagnosis when seen in the fetus of a parent with the disease. Since renal function in utero is adequate, oligohydramnios is not present.
Degree of confidence
Ultrasonography is the procedure of choice in the workup of patients with ADPKD. It is also an ideal modality for screening the family of patients with known disease and for routine follow-up in patients.
Ultrasonographic technology has improved tremendously, and, with state-of-the-art ultrasonographic machines, cysts that are a few millimeters in size can be depicted.
Renal cysts similar to those associated with ADPKD can occur as simple renal cysts without genetic etiology or can arise in von Hippel–Lindau disease, in acquired uremic cystic disease (in which kidneys are small, with no renal function), in patients on hemodialysis, or in patients who have had renal transplantation.
In ARPKD, the kidneys are hyperechoic and enlarged, but the cysts are too small to be depicted on ultrasonographic images; however, discrete macroscopic cysts (usually < 1 cm) occasionally are seen in patients with ARPKD.
Technetium-99m (99m Tc) mercaptotriglycylglycine or other radionuclides are employed in isotope renography, which is a useful procedure for assessing renal function and avoiding the nephrotoxic effects of iodinated contrast media. On analog images, cysts are demonstrated as photon-deficient masses.
Similarly, uptake of99m Tc dimercaptosuccinic acid shows the cysts as multiple photon-deficient masses.
Hepatic and splenic cysts also are photopenic on scans using99m Tc sulfur colloid. Infected cysts, when scanned with granulocytes labeled with99m Tc hexamethylpropyleneamine oxime, may demonstrate increased activity. Similarly, they may be avid for gallium-67 citrate.
Degree of confidence
Although isotopic renography is an excellent modality for assessing absolute and relative renal function, its role in the diagnosis of autosomal dominant polycystic kidney disease is limited.
Multiple photon-deficient renal masses may occur with simple cysts, granulomas, abscesses, and multiple tumors.
Angiographic criteria for cystic renal disease are well established. In the arterial phase, intrarenal arterial branches are stretched and displaced around the cysts, as seen in the image below.
The cysts are seen as sharply defined, radiolucent masses. The cyst walls appear thin and smooth, and an acute angle is characteristic between the cyst and the normal renal cortex, forming a beak (as seen in the image below). In the nephrogram phase, avascular areas of varying sizes are demonstrated, giving rise to a Swiss cheese appearance, as on an intravenous urogram.
Hemorrhagic and infected cysts may have abnormal vessels simulating the neovascularity of a neoplasm. Hepatic and splenic cysts appear as avascular masses on a flush aortogram or on selective visceral angiography (see the image below).
Degree of confidence
Angiography has a high degree of sensitivity in the diagnosis of autosomal dominant polycystic kidney disease (ADPKD), but its specificity is low.
Differentiation from simple renal cysts is not always possible; avascular tumors also may pose problems. Renal sinus fibrolipomatosis may superficially resemble cysts associated with ADPKD.
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