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Multicystic Dyplastic Kidney


Multicystic Dyplastic Kidney

Findings:

Multiple cysts of varying sizes are seen in the right paraspinous location. No normally appearing kidney was identified and the contralateral kidney, bladder and amniotic fluid were all normal. This is most consistent with a multicystic dysplastic kidney.

Discussion:

In this case and most cases of multicystic dysplasia, it is the finding of large fluid filled cysts in a paraspinous location that is most striking to the sonologist. While this finding may be confused with other entities such as hydronephrosis it is unlikely it will be missed unless: the examination is technically difficult, the scans are done very early or their is involution of the cystic dysplasia (discussed below). In the past, most pediatricians have recognized multicystic dysplastic kidneys when they were discovered as a flank mass at the time of a neonatal examination. With the advent of improved ultrasound instrumentation and a better understanding of the appearance of the disease, many, if not most, cases are now detected at the time of antenatal sonography.

Multicystic dysplasia of the kidney, as well as most forms or renal dysplasia are likely due to renal obstruction during embryogenesis. Normal renal development is dependent upon the interaction of the metanephric bud and the metanephric blastema which begins during the seventh menstrual week. This interaction results in the formation of calyces, tubules and nephrons which continue until term. Complete obstruction or atresia impairs ureteral branching and results in decreased division of collecting tubules and inhibition of induction and maturation of nephrons. The collecting tubules enlarge and develop cysts in their terminal portions. These cysts of various sizes are distributed randomly throughout the abnormal kidney and are held together by connective tissue, without macroscopic evidence of intercommunication of cysts. Experimental evidence in lambs has shown that if occlusion of the ureters occurs in utero between 50-60 days gestation (which is equivalent to about 110-120 days gestation in the human) multicystic renal dysplasia will result and be detected at the time of delivery. In muticystic renal dysplasia the renal pelvis and or ureter are usually atretic. In this and other forms of dysplasia, the more proximal the level of obstruction, the more likely the cysts will be large as in MCKD. It has been hypothesized by Pathak et al that this is a result of the pressure effects on the kidney from the obstruction. Their theory is that obstruction at a higher level results in calyces that are markedly distended with cyst formation, when the level is more distal, at the urethra, as in posterior urethral valves, the pressure effects are more generalized and less severe, so that the calyces do not distend as much. Thus kidneys will become dysplastic, however with much smaller and less visible cysts. During embryonic development the central elements from first and the more peripheral elements form later. While multicystic dysplastic kidney disease may affect both central and peripheral elements, obstruction occuring later in fetal life will result in more peripheral cystic dysplasia (Type IV cystic disease).

Although the kidney in multicystic dysplasia is usually described as having no renal function, there is evidence that these kidneys may have some component of residual renal function. Microscopic examination of the MCDK has shown that the number of nephrons are reduced but are seldom absent. Likewise, although glomeruli are primitive, normal glomeruli may be present. The change in size of the cysts in multicystic renal dysplasia are likely related to the number of preserved glomeruli and thus the degree of residual renal function. As long as the kidney is able to filter plasma, the overall size will increase. As the nephrons become fibrotic, the amount of filtrate will diminish ahd the growth of the kidney will stop. In the study by Hashimoto et al, in no case did a multicystic dysplastic kidney shrink initially and then subsequently enlarge later in gestation. In a study by Strife et al serial sonographic examinations over an average of 30 months revealed a decrease in the size of the kidney over time in 67%, no change in 19% and and increase in size of the cysts and kidney in 10%. The first ultrasound finding in their study was a change in cyst distention, which preceded a decrease in renal size. As the cysts became less prominent, dyplastic changes (increase in echogenicity) became more prominent. Thus the appearance of the kidney will depend upon the time in gestation and the spectrum of disease. Cysts may be quite large, as in the classic description of multicystic dysplasia, or the kidney may be echogenic and dysplastic or small and involuted. Cases have been reported in which classical large cysts characteristic of MCKD were seen in utero however at the time of surgery, there was no evidence of renal tissue or its vessels. This suggests that some cases of renal a.genesis may be due to involuted cases of multicystic kidney disease.

Multicystic Dyplastic Kidney with a large cyst, increasing in size

Multicystic dyplastic kidney disease is associated with contralateral renal disease in a significant number of patients. Previous reports have shown that MCDK is associated with a 20%-45% incidence of contralateral renal anomalies. In a number of studies the most common contralateral abnormality was vesicoureteral reflux and ureteropelvic junction obstruction. In the study by Kleiner et al the overall rate of contralateral renal abnormalities was 41%. Lethal fetal renal disease was seen in 30% (bilateral MCDK in 19% and contralateral renal agenesis in 11%). Contralateral hydronephrosis was seen in 7%. If the amniotic fluid volume and fetal bladder are normal follow-up studies should be performed to evaluate progression of disease and more importantly anatomic status and function of the remaining kidney.

Bilateral Multicystic Dyplastic Kidneys

Anhydramnios in same case

As was mentioned above, the multicystic kidney is a dysplastic kidney which has been classified by Potter et al as type II disease. Subsequently, this type has been subclassified into two groups: type IIa and type IIb. The more common type IIa is secondary to pelvoinfundibular atresia; the remaining type IIb, is the hydronephrotic form. The pelvoinfundibular atresia and resulting dysplasia of MCKD is thought to come from a vascular insult. There have been familial cases reported and an interesting case in which an ipsilateral multicystic dysplastic kidney appearing in identical twins has also been reported.

Potter Classification of Renal Dysplasia

Type I

Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Type IIa

Multicystic Dysplastic Kidney Disease [Pelvo-infundibular atresia] (MDKD)

Type IIb

Multicystic Dysplastic Kidney Disease [Hydronephrotic type] (MDKD)

Type III

Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Type IV

Cystic Dysplasia due to Urethral Obstruction

The sonographic findings of a multicystic dysplastic kidney are usually quite striking. The typical reniform appearance is lost, little parenchyma remains having been replaced by multiple randomly positioned non-communicating cysts of various sizes. The largest cyst is not medial in location. These findings are in contradistinction to hydronephrosis in which the reniform contour is maintained, and the fluid-filled collecting system (calyces, infundibula and renal pelvis) are anatomically arranged and communicate with one another. Any remaining non-atrophic parnechyma is peripherally located to the fluid filled structures.

Multicystic Dyplasia with multiple non-communicating cysts of varying sizes
Hydronephrosis; the dilated calyces (arrows) communicate with the renal pelvis

 

A recent study by Lazebnik et al evaluated a large series of patients with multicystic dysplastic kidney disease with follow-up. The authors reported their analysis of a retrospective review of fetuses with the sonographic diagnosis of multicystic dysplastic kidney disease (MCDK) from two hospitals from 1986-1992 and 1991-1996. Inclusion criteria were prenatal sonographic diagnosis of MCDK and confirmed by either fetal tissue on autopsy, or confirmatory postnatal ultrasound and or renal scintigraphy. Of note, only those with either prenatal or postnatal chromosome studies were included. Sonographic criteria for the diagnosis of MCDK included echogenic renal parenchyma, multiple cysts of varying sizes that did not communicate at the periphery of the kidney and no sonographic findings suggestive of obstuctive uropathy. There were 102 patients that met the criteria for inclusion. 54% of patients were referred to confirm a sonographic detected abnormality. Unilateral MCDK was present in 38% in the right kidney and 38% in the left kidney. 24% of fetuses had bilateral disease. Among fetuses with unilateral disease, the contralateral kidney was normal in 74%, affected by a pathology other than MCDK in 15%, absent in 9% or ectopic in location in 1%. 35% of fetuses had associated non-renal abnormalities. The most common abnormalities were those of the heart, followed by the spine, extremities, face and umbilical cord. Fetuses with bilateral MCDK were more likely to have associated non-renal abnormalities 16/24 in comparison with fetuses with unilateral MCDK 20/78. 10 fetuses (9.8%) had abnormal chromosomes. Female fetuses (6/30) were more likely to have an abnormal chromosome study than male fetuses (4/72). A higher percentage of fetuses with bilateral MCDK disease (4/24) had an abnormal karyotype than fetuses with unilateral MCDK (6/78). No karyotype abnormalities were found in fetuses with unilateral MCDK if an associated non-renal abnormality was not found. The ratio of male to female fetuses was 2.4:1. Female fetuses were twice as likely to have bilateral MCDK as males. Of patients continuing their pregnancy, six fetuses (9%) had incomplete involution of the affected kidney. Voiding cystourethrography was done on 13 patients. 3/13 (23%) newborns had reflux in the contralateral kidney.

In the past most neonates would have these kidneys surgically removed, usually due to the risk of infection and neoplasm. As most patients with multicystic dysplastic kidneys have pelvo-ureteral atresia on the affected side, it is unlikely that infected urine will reflux into the kidney. In the last 2 decades there have been at least six reported cases of reported malignancies in these kidneys. Although the potential risk for neoplasia exists, research utilizing flow cytometry attempting to show a relationship between dysplasia and neoplasia (looking for abnormal DNA) of the MCDK has found no evidence of neoplasia.

References:

Strife JL, Souza AS, Kirks DR, Strife CF et al . Multicystic dysplastic kidney in children: US follow-up. Radiology 186:785-788, 1993

Avni EF, Thoua Y, Lalmand B et al. Multicystic dyplastic kidney:evolving concepts-in utero diagnosis and post-natl follow-up by ultrasound. Ann Radiol 29:663-668, 1986

Gordon AC, Thomas DF, ARthur RJ, Irving HC. Multicystic dysplastic kidney: is nephrectomy still appropriate? J Urol 140:1231-1234, 1988

Jung WH, Peters CA, Mandell J, Vawter GF, Retik AB. Flow cytometric evaluation of multicystic dysplastic kidneys. J Urol 144:413-415, 1990

Hashimoto BE, Filly RA, Callen PW. Multicystic dysplastic kidney in utero: changing appearance on US. Radiology 159:107-109, 1986

Sanders RC, Nussbaum AR, Solez K. Renal dysplasia: sonographic findings. Radiology 167:623-626, 1988

Beck AD. The effect of intrauterine urinary obstruction upon the development of the fetal kidney. J Urol 105:784-789, 1971

Pathak IG, Williams DI. Multicystic and cystic dysplastic kidneys. Br J Urol 36:318-331, 1963

Fillon R, Grignon A, Boisvert J Antenatal diagnosis of ipsilateral multicystic kidney in identical twins. J Ultrasound Med 4:211-212, 1985

Felom B, Cussen LJ. The hydronephrotic type of unilateral congenital multicystic disease of the kidney. Semin Roentgenol 10:113, 1975

Griscom WT, Vanter GF, Fellers FX. Pelvoinfundibular atresia: the usual form of multicystic kidney. Semin Roentgenol 10:125, 1975

Potter EL, Craig JM. Pathology of the fetus and infant. 3rd Ed. p 448

Goldstein RB. Cystic renal disease in the infant and fetus: the sonographic perspective. 1989 Year Book of Pediatric Radiology, 23-25, 1989

Lazebnik N, Bellinger MF, Ferguson JE, Hogge JS, Hogge WA. Insights into the Pathogenesis and Natural History of Fetuses with Multicystic Dysplastic Kidney Disease Prenatal Diagn 19:418-23, 1999

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California