Multicystic Dysplastic Kidney Imaging

Introduction:

Multicystic dysplastic kidney (MCDK) is a common congenital kidney disorder that can be detected in prenatal ultrasound. MCDK is characterized by the replacement of an entire kidney with irregularly arranged multiple cysts without normal parenchyma. The exact cause of MCDK is not known. The genetic mutation of the EYA1, SIX1, or PAX2 genes, intake of certain medication during pregnancy, or family history can cause blockage in the kidney along the path of the urinary flow during the development of the fetus in the womb. It is often unilateral and rarely bilateral.

What Are the Different Types of Multicystic Dysplastic Kidneys?

1) Unilateral MCDK :

• In unilateral MCDK, one of the fetus's kidneys fails to develop properly in the womb. It does not cause any problems in childbirth.

• Children with only one properly functioning kidney do not require treatment and do not have any complications.

• Sometimes the normal kidney increases in size to compensate for the missing kidney; however, they might be at risk of hypertension or urinary tract infection.

2) Bilateral MCDK:

• In bilateral MCDK, both the kidneys of the fetus fail to develop properly in the womb. Bilateral MCDK is rare; such children cannot survive as both kidneys lack function.

• In ultrasound, bilateral MCDK appears as multiple cysts of various sizes, and it resembles a bunch of grapes.

What Are the Imaging Techniques Used in the Diagnosis of Multicystic Dysplastic Kidneys?

Radiography:

• In kidney, ureter, and bladder (KUB) images, MCDK appears as a displaced bowel due to an enlarged kidney.

• In plain images, the calcification of the cystic wall has a ring-like appearance.

• The atretic or absent ureter can be demonstrated in retrograde pyelography.

Ultrasound:

• In patients with multicystic dysplastic kidneys, ultrasound shows a lack of normal surrounding renal parenchyma.

• High-resolution probes of the ultrasound show a small amount of echogenic dysplastic undifferentiated tissue.

• Bilateral MCDK is often associated with anhydramnios or oligohydramnios and results in prenatal death due to inadequate lung development.

• Unilateral MCDK is often associated with urogenital tract anomalies, and 15 percent of patients show extrarenal anomalies.

• The contralateral kidney should be assessed for dysplastic changes and congenital uropathies, which can affect the overall prognosis.

• Cystic and renal hyperechogenicity are the major findings of renal cystic disease in the fetus that resembles a glomerular cyst, renal cyst, or renal tubular dilation.

• Renal hyperechogenicity can be visualized only in the cortex, medulla, or the entire kidney.

• During the later gestational period, hyperechogenicity is confirmed by comparing the hyperechoic renal cortex with the liver, seminal vesicle, or testis.

Antenatal Ultrasound:

• The 20th-week antenatal ultrasound helps detect MCDK when the fetus is in the womb.

• Unilateral MCDK is suspected in antenatal ultrasound when one of the kidneys looks different from another normal kidney.

• This scan also measures the amniotic fluid level. Normally, the fetus's kidney makes urine and passes it into the amniotic fluid. In pregnant women with oligohydramnios (less amniotic fluid), the fetus's kidneys are not functioning well.

Magnetic Resonance Imaging Scan:

• A magnetic resonance imaging (MRI) scan shows the multicystic appearance of the multicystic dysplastic kidney (MCDK) with little or no parenchyma.

• T2-weighted images help visualize the cystic involvement, while T1 and T2-weighted images are used to delineate the outline of the kidney and determine total kidney volume.

• Contrast-enhanced T1-weighted images are used to detect tumors and hemorrhages, whereas diffusion-weighted MRI sequences help detect the tumors.

• In patients with impaired kidney function, macrocyclic gadolinium chelates should be used as a contrast agent.

• In infants less than one year or patients having an estimated glomerular filtration rate of less than 60 mL/minute. 1.73 m2, the gadolinium-based contrast materials should be used with caution and are not indicated twice within seven days.

• History of allergic reactions to the contrast material in patients should be considered before their administration.

• MRI usually requires sedation in children; hence an ultrasound is preferred over MRI.

• MRI is indicated only when there is suspicion of a tumor in multiple cysts and in the measurement of total kidney volume.

Nuclear Imaging:

• Nuclear renograms help assess the function, perfusion, and drainage of the kidneys.

• In nuclear imaging study, the functioning kidney uptake the radiotracer and excretes it into the ureter, bladder, and renal pelvis.

• The radionuclides used to detect MCDK are MAG-3, diethylenetriamine-pentaacetic acid (DTPA), and dimercaptosuccinic acid (DMSA).

Voiding Cystourethrogram:

• In MCDK patients voiding cystourethrography (VCUG) is used to evaluate vesicoureteral reflux and ipsilateral ureterocele.

• Voiding cystourethrogram (VCUG), also known as micturating cystourethrogram (MCUG), is a specialized imaging technique used to assess the structure and function of the lower urinary tract, in particular, the bladder and the urethra. This test is performed on both children and adults. It is most commonly used in children to detect urinary tract infections.

• A thin, flexible tube called a catheter coated with numbing gel will be inserted into the urethra (an opening from where the urine comes out of the body) and passed into the bladder. The tube will be safely taped in place so that it will not move during the procedure. Contrast material (a special dye) flows through the catheter into the bladder until it is completely filled.

• This contrast material shows the urinary tract as a bright white color on the X-ray. X-rays are taken from different angles. Using fluoroscopy (a special X-ray technique), the radiologist will get images of bladder filling and emptying. After that, the catheter is removed so that patients can urinate. Images are taken while they empty their bladder.

• Once the bladder is empty, a final X-ray is taken. This test is used to detect the backward flow of urine into the ureters or kidneys.

Conclusion:

Ultrasound is helpful in the evaluation of the kidney in MCDK during the follow-up of conservative treatment. MCDK should be differentiated from segmental cystic dysplasia, renal lymphangioma, and cystic tumors. About 1 in 4300 babies were born with unilateral MCDK. Nuclear imaging is an effective imaging technique used to differentiate MCDK from hydronephrosis. As babies with MCDK are often associated with heart problems echocardiogram is often recommended.