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Renal cystic disease—An overview
Renal Cystic Disease- An Overview Milton Elkin, M.D.
T
HERE HAVE BEEN a number of classifications of renal cysts,2p6 and more will undoubtedly appear, indicating weaknesses in those already proposed. The major advantage of classification is to clear up the many confusions in terminology of the various types of renal cystic disease. It is not uncommon to see a report describing a condition in terms which in another classification refer to a different entity. This confusion is ascribable not only to the nephrologist and radiologist, but also to the usually accepted “final judge,” the pathologist. I recently read the report of a surgical specimen rendered by an excellent pathologist with the following diagnostic terms used interchangeably: multilocular cystic kidney, multiple cysts of the kidney, and multicystic kidney. These are all different entities, as will be demonstrated later in this Seminar. Purupelvic cyst is an extrarenal lesion, occurring most frequently in the renal hilum; peripelvic cyst is another name for pyelogenic cyst or calyceal diverticulum. The sponge kidney of the infant is polycystic disease of the newborn; medullary sponge kidney is seen usually in the adult and consists of ectasia of the collecting ducts. Classification consists in groupings of conditions with some sort of common or related denominator. If causes were known, an etiologic classification would be satisfactory-eg, cysts due to obstruction, cysts due to underlying vascular disease, cysts due to infection, etc. However, the etiology of most renal cysts has not been clearly established. For congenital cysts, specific embryologic developmental defects might serve as the basis for classification. Again, there is no agreement on the nature of the defects, and a classification of this sort would leave too many renal cysts unclassified. A pathologic classification based on histologic criteria has not been feasible because the histologic changes are, for the most part, not specific enough. A clinical classification, using such parameters as age of occurrence, or of death, the presence of hypertension, or of renal insufficiency, or Milton Elkin, M.D.: Chairman and Professor of Radiology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, N. Y. 10461. 0 I9 75 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol.
X, No. 2 (April),
1975
prognosis has too much overlap for satisfactory use. The clinical course of unilateral renal dysplasia with cysts is quite different from bilateral renal dysplasia with cysts, even though the underlying kidney abnormality is the same. POTTER
CLASSIFICATION
(TABLE
1)
Osathanondh and Potter’ published several papers in 1964 describing their conclusions as to the pathogenesis of polycystic kidneys, based primarily on microdissection studies. To put all renal cysts into a Potter classification, one would have to believe that all cysts result from abnormality in development, and that they are all variants of polycystic kidneys. Osathanondh and Potter stated that in all types of polycystic kidney the chief abnormality is in the collecting ducts. As the ureteral bud goes through its many dichotomous divisions, the expanded growing zone at the end of the tubule is the ampulla; the formed portion of the dividing bud, left behind as the ampulla advances, is the interstitial portion. Potter type 1 supposedly results from hyperplasia of the interstitial portions of the collecting tubules (ie, excessive growth of the cells of the interstitial portion) after induction and attachment of nephrons from the metanephrogenic blastema. This is the polycystic kidney of the newborn, always bilateral and incompatible with prolonged survival. Potter type 2 is attributed to inhibition of ampullary activity resulting in a reduction in the number of generations of collecting ducts derived from the ureteral bud, the inadequately branched collecting ducts terminating in cysts, with marked diminution or absence of nephrons. In this group are included the dissimilar entities of dysplasia (multicystic kidney) and multilocular cyst. In Potter type 3, the developmental abnormalities are believed to involve the collecting ducts (from the ureteral bud) as well as the nephrons and connective tissue (from the metanephrogenic blastema) in a scattered fashion, so that normal collecting ducts and nephrons are intermixed with the abnormal. The cysts may occur in relation to either the collecting ducts or the nephrons. The conditions in this group are polycystic kidneys 99
100
MILTON Table
Mechanism
1. Osathanondh and Potter Classification Polycystic Kidneys of Production
Clinical
of
1: Hyperplasia interstitial portions of
Type
2: Inhibition of ampul. lary activity
Multicystic kidney Multilocular cyst Aplastic kidney
Type
3: Multiple abnormalities of kidney development
Adult type polycystic kidneys Cysts in trisomy Cysts in tuberous sclerosis Medullary sponge kidney
Type 4: Injury to ampullae from pressure due to urethral obstruction
Renal cysts in infant with posterior urethral valves
collecting
2. Classification (Modified
Entities
Type
Infantile
Table
polycystic
tubules
of the adult, the cysts in trisomy syndromes, the cysts in tuberous sclerosis, and medullary sponge kidney. The clinical and prognostic import of these conditions are so disparate that putting them into the same group is difficult to accept. They have no radiologic similarities. Potter type 4 is supposedly due to injury to the ampulla by increased back pressure resulting from urethral obstruction (eg, by urethral valves) with production of cysts in collecting ducts and nephrons. There appears to be little justification for regarding all renal cysts as different degrees of polycystic kidneys. Not all cysts are developmental; some are clearly acquired.
In 1968 Grossman, Winchester, and Chisari4 reported a classification of renal cystic disease on the basis of the roentgenographic appearance at urography (Table 3). They made an attempt to translate the developmental aberrations of the Potter classification into roentgenographic patterns. I find this classification confusing and of limited value. Even though the classical case of polycystic kidneys of the newborn shows on the urogram linear streaks of contrast medium radiating to the cortex, representing puddling of opacified urine in the dilated and elongated collecting tubules, this finding is seen only in the minority of patients. Usually the renal function is too poor to show much more than a faint nephrogram of the bilaterally enlarged kidneys. Further, grouping together (under Type II) of the severely disTable
OTHER
3. Classification (Modified
CLASSIFICATIONS
In 1967, Gleason, McAlister, and Kissane3 proposed a classification of renal cystic disease in children with an attempt at a radiologic-pathologic correlation. They suggested that the changes in the dysplastic cystic kidney (multicystic kidney) associated with absent, stenotic, or atretic ureter may represent intrauterine developmental changes due to the ureteral obstruction, with subsequent abnormal or abortive differentiation of nephrogenie tissue. They stated that segmental dysplasia can occur, usually in the upper portion of a kidney with a duplex pelvis, with the ureter from the upper pelvis obstructed due to stenosis, atresia, or ectopia. This classification (Table 2) is a very useful one for the radiologist, including practically all the types of renal cysts recognized clinically. There is no attempt to define mechanisms of development for all the lesions.
of Cystic Disease of the Kidney From Gleason et al.)
A. Renal dysplasia B. Polycystic renal disease 1. Adult type 2. Infantile type C. Medullary cystic disease 1. Sponge kidney 2. Uremic medullary cystic disease D. Simple renal cysts E. Multilocular renal cysts F. Calyceal diverticula G. Miscellaneous cysts of renal origin H. Cysts of other than nephric origin
kidneys
.-
ELKIN
Type
I.
Type
II.
Type
I II.
Type
IV.
of Cystic Diseases of the Kidney From Grossman et al.)
Contrast medium in dilated collecting tubules A. Polycystic kidneys of the newborn B. Medullary sponge kidney C. Renal tubular ectasia with congenital hepatic fibrosis Nonfunction throughout or in part of kidney; contour changes in renal outline and collecting system A. Multicystic kidney B. Hypoplastic cystic kidney C. Multilocular cysts D. Simple cysts E. Uremic medullary cystic disease Deformity of renal pelvis and calyces by cysts intermixed with normally functioning tissue A. Adult polycystic kidneys B. Tuberous sclerosis Small cortical and/or medullary cysts secondary to distal urinary tract obstruction A. Posterior urethral valves B. Other obstructions in urethra
RENAL
CYSTIC
101
DISEASE
organized dysplastic multicystic kidney with the kidney containing simple cysts is an organogenesis morass. Tuberous sclerosis is included in Type III along with adult polycystic kidneys because of possible urographic similarities. However, it does not seem reasonable to introduce the angiomyolipomas of tuberous sclerosis into a classification of cysts. Cysts can occur in tuberous sclerosis but these are usually not similar to those of polycystic kidneys. CLASSIFICATION
USED
IN THIS
SEMINAR
In 1969, Elkin and Bernstein’ proposed a classification of cystic disease of the kidney, drawn in part from previous classifications.2-6 Its aims included: (1) group individually the well accepted entities, such as dysplasia and polycystic disease; (2) group anatomically (cortex or medulla) those entities with questionable pathogenesis; (3) group the remaining unusual intrarenal cysts under “miscellaneous”; (4) separate out the extraparenchymal renal cysts. It was hoped that this classification could be kept simple and still be of value to the radiologist. It was also hoped that the classification would promote agreement on terminology. It is a modification of this classification (Table 4) which is used as the basic configuration of this issue of Seminarsin Roentgenology. The classification still suffers from lumping together conditions with little or no clinical relationships.
Questions There still is no completely satisfactory classification of cystic diseases of the kidney since there is as yet no firm basis for categorization. Some of the entities are definitely of genetic nature; some are probably acquired in utero; some are acquired at different stages of postnatal life. In most types of renal cystic disease there is little inkling as to mechanisms of development. It is improper to categorize all cysts of the kidney as forms of polycystic disease. Among the many questions still to be answered in respect to renal cystic diseases, there are a few of special interest. Are the changes of the multicystic kidney due to in utero ureteral obstruction? Multicystic kidney is associated with atresia or stenosis of its ureter; possibly the renal abnormality is secondary to the ureteral obstruction in the embryo or fetus. Dr. Felson’s article deals with this mechanism in detail. Does focal multicystic kidney occur? The entity of multicystic kidney has been described as in-
Table
4. Classification of Cystic Diseases of the Kidney (Modified From Elkin and Bernstein)
I. Renal dysplasia A. Multicystic kidney B. Focal and segmental dysplasia C. Multiple cysts associated with lower urinary tract obstruction D. Hereditary and familial cystic dysplasia I I. Polycystic disease A. Polycystic disease of the young 1. Polycystic disease of the newborn 2. Polycystic disease of childhood B. Adult type polycystic disease I I I. Cortical cysts A. Trisomy syndromes B. Tuberous sclerosis C. Simple cyst (solitary or multiple; unilateral or bilateral) D. Multilocular cyst IV. Medullary cysts A. Medullary sponge kidney B. Medullary cystic disease (uremic) C. Medullary necrosis D. Pyelogenic cyst V. Miscellaneous intrarenal cysts A. Inflammatory (tuberculosis, calculus disease, echinococcus disease) B. Neoplastic (cystic degeneration of neoplasm) C. Traumatic (intrarenal hematoma) VI. Extraparenchymal cyst A. Parapelvic cyst B. Perinephric cyst
volving the entire kidney, unilateral or bilateral. There have been occasional reports of involvement confined to one subdivision of a duplicate kidney, with atresia or stenosis of the ureter draining it. This is still consistent with an obstructive pathogenesis for multicystic kidney. Focal involvement in a kidney with a normal renal pelvis and ureter would be difficult to explain by an obstructive mechanism unless one were to consider focal zones of obstruction in the infundibular-calyceal system. Does infantile polycystic renal disease always lead to death in the neonatal period? We have had one documented exception. This neonate had high-degree renal failure, symmetrically enlarged kidneys and heterogenous nephrogram typical of multiple cysts. At exploratory laparotomy, the kidneys had the characteristic gross appearance of infantile polycystic disease. Yet this child has survived for over 3 yr, the kidneys are now normal in size, and the BUN only moderately elevated. Is adult polycystic kidney a delayed form of infantile polycystic kidney, or are the two completely unrelated? Does there exist a mild form of
102
infantile polycystic kidney, in which the cysts are too small and too few to produce clinically detectable kidney abnormalities, and from which later in life (with growth of the cysts at varying rates and the development of additional cysts) the picture of adult polycystic kidney evolves? There is no evidence for this. The weight of opinion favors the view that there is no relationship between the two entities. How good are the radiologic criteria for the diagnosis of adult polycystic kidneys? The disease may progress asymmetrically; so the kidneys need not be equally involved. In fact, one kidney may be severely involved in characteristic fashion, and the other appear normal. A patient with multiple simple cysts in one kidney may present with the same urographic findings. Similarly, multiple simple cysts of both kidneys may show a urographic appearance similar to that of polycystic kidneys with bilateral changes. Even the pathologist may have difficulty in this regard. An angiographic sign has been used to make this differentiation. In the polycystic kidney, the renal contour and pelvicalyceal deformities are due to the many large cysts. The nephrogram of those portions of the cortex not involved by large cysts appears heterogenous because it is peppered with
MILTON
ELKIN
the lucencies of the small cysts. The kidney with multiple simple cysts shows a normal, homogeneous nephrogram between the cysts. However, the small cysts of polycystic kidney may be too small or too sparse to be discerned. To my knowledge, serial angiographic studies have not been done on a patient before the development of the typical urographic picture of polycystic kidneys. It is an intriguing conjecture that early in life some of these individuals may show a normal urographic and angiographic appearance. REFERENCES 1. Elkin M, Bernstein J: Cystic disease of the kidneyradiological and pathological considerations. Clin Radio1 20:65-82, 1969 2. Emmett JL, Witten DM: Clinical Urography, An Atlas and Textbook of Roentgenologic Diagnosis (ed 3). Philadelphia, WB Saunders, 1971, pp 931-1045 3. Gleason DC, McAlister WH, Kissane J: Cystic disease of the kidneys in children. Am J Roentgen01 100: 135146, 1967 4. Grossman H, Winchester PH, Chisari FV: Roentgenographic classification of renal cystic disease. Am J Roentgen01 104: 319-331, 1968 5. Osathanondh V, Potter EL: Pathogenesis of polycystic kidneys. Arch Path01 77:459-465, 5 10-5 12, 1964 6. Spence HN, Baird SS, Ware EW Jr: Cystic disorders of the kidney. Classification, diagnosis, treatment. JAMA 163: 1466-1412, 1957
T
HERE HAVE BEEN a number of classifications of renal cysts,2p6 and more will undoubtedly appear, indicating weaknesses in those already proposed. The major advantage of classification is to clear up the many confusions in terminology of the various types of renal cystic disease. It is not uncommon to see a report describing a condition in terms which in another classification refer to a different entity. This confusion is ascribable not only to the nephrologist and radiologist, but also to the usually accepted “final judge,” the pathologist. I recently read the report of a surgical specimen rendered by an excellent pathologist with the following diagnostic terms used interchangeably: multilocular cystic kidney, multiple cysts of the kidney, and multicystic kidney. These are all different entities, as will be demonstrated later in this Seminar. Purupelvic cyst is an extrarenal lesion, occurring most frequently in the renal hilum; peripelvic cyst is another name for pyelogenic cyst or calyceal diverticulum. The sponge kidney of the infant is polycystic disease of the newborn; medullary sponge kidney is seen usually in the adult and consists of ectasia of the collecting ducts. Classification consists in groupings of conditions with some sort of common or related denominator. If causes were known, an etiologic classification would be satisfactory-eg, cysts due to obstruction, cysts due to underlying vascular disease, cysts due to infection, etc. However, the etiology of most renal cysts has not been clearly established. For congenital cysts, specific embryologic developmental defects might serve as the basis for classification. Again, there is no agreement on the nature of the defects, and a classification of this sort would leave too many renal cysts unclassified. A pathologic classification based on histologic criteria has not been feasible because the histologic changes are, for the most part, not specific enough. A clinical classification, using such parameters as age of occurrence, or of death, the presence of hypertension, or of renal insufficiency, or Milton Elkin, M.D.: Chairman and Professor of Radiology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, N. Y. 10461. 0 I9 75 by Grune & Stratton, Inc. Seminars
in Roentgenology,
Vol.
X, No. 2 (April),
1975
prognosis has too much overlap for satisfactory use. The clinical course of unilateral renal dysplasia with cysts is quite different from bilateral renal dysplasia with cysts, even though the underlying kidney abnormality is the same. POTTER
CLASSIFICATION
(TABLE
1)
Osathanondh and Potter’ published several papers in 1964 describing their conclusions as to the pathogenesis of polycystic kidneys, based primarily on microdissection studies. To put all renal cysts into a Potter classification, one would have to believe that all cysts result from abnormality in development, and that they are all variants of polycystic kidneys. Osathanondh and Potter stated that in all types of polycystic kidney the chief abnormality is in the collecting ducts. As the ureteral bud goes through its many dichotomous divisions, the expanded growing zone at the end of the tubule is the ampulla; the formed portion of the dividing bud, left behind as the ampulla advances, is the interstitial portion. Potter type 1 supposedly results from hyperplasia of the interstitial portions of the collecting tubules (ie, excessive growth of the cells of the interstitial portion) after induction and attachment of nephrons from the metanephrogenic blastema. This is the polycystic kidney of the newborn, always bilateral and incompatible with prolonged survival. Potter type 2 is attributed to inhibition of ampullary activity resulting in a reduction in the number of generations of collecting ducts derived from the ureteral bud, the inadequately branched collecting ducts terminating in cysts, with marked diminution or absence of nephrons. In this group are included the dissimilar entities of dysplasia (multicystic kidney) and multilocular cyst. In Potter type 3, the developmental abnormalities are believed to involve the collecting ducts (from the ureteral bud) as well as the nephrons and connective tissue (from the metanephrogenic blastema) in a scattered fashion, so that normal collecting ducts and nephrons are intermixed with the abnormal. The cysts may occur in relation to either the collecting ducts or the nephrons. The conditions in this group are polycystic kidneys 99
100
MILTON Table
Mechanism
1. Osathanondh and Potter Classification Polycystic Kidneys of Production
Clinical
of
1: Hyperplasia interstitial portions of
Type
2: Inhibition of ampul. lary activity
Multicystic kidney Multilocular cyst Aplastic kidney
Type
3: Multiple abnormalities of kidney development
Adult type polycystic kidneys Cysts in trisomy Cysts in tuberous sclerosis Medullary sponge kidney
Type 4: Injury to ampullae from pressure due to urethral obstruction
Renal cysts in infant with posterior urethral valves
collecting
2. Classification (Modified
Entities
Type
Infantile
Table
polycystic
tubules
of the adult, the cysts in trisomy syndromes, the cysts in tuberous sclerosis, and medullary sponge kidney. The clinical and prognostic import of these conditions are so disparate that putting them into the same group is difficult to accept. They have no radiologic similarities. Potter type 4 is supposedly due to injury to the ampulla by increased back pressure resulting from urethral obstruction (eg, by urethral valves) with production of cysts in collecting ducts and nephrons. There appears to be little justification for regarding all renal cysts as different degrees of polycystic kidneys. Not all cysts are developmental; some are clearly acquired.
In 1968 Grossman, Winchester, and Chisari4 reported a classification of renal cystic disease on the basis of the roentgenographic appearance at urography (Table 3). They made an attempt to translate the developmental aberrations of the Potter classification into roentgenographic patterns. I find this classification confusing and of limited value. Even though the classical case of polycystic kidneys of the newborn shows on the urogram linear streaks of contrast medium radiating to the cortex, representing puddling of opacified urine in the dilated and elongated collecting tubules, this finding is seen only in the minority of patients. Usually the renal function is too poor to show much more than a faint nephrogram of the bilaterally enlarged kidneys. Further, grouping together (under Type II) of the severely disTable
OTHER
3. Classification (Modified
CLASSIFICATIONS
In 1967, Gleason, McAlister, and Kissane3 proposed a classification of renal cystic disease in children with an attempt at a radiologic-pathologic correlation. They suggested that the changes in the dysplastic cystic kidney (multicystic kidney) associated with absent, stenotic, or atretic ureter may represent intrauterine developmental changes due to the ureteral obstruction, with subsequent abnormal or abortive differentiation of nephrogenie tissue. They stated that segmental dysplasia can occur, usually in the upper portion of a kidney with a duplex pelvis, with the ureter from the upper pelvis obstructed due to stenosis, atresia, or ectopia. This classification (Table 2) is a very useful one for the radiologist, including practically all the types of renal cysts recognized clinically. There is no attempt to define mechanisms of development for all the lesions.
of Cystic Disease of the Kidney From Gleason et al.)
A. Renal dysplasia B. Polycystic renal disease 1. Adult type 2. Infantile type C. Medullary cystic disease 1. Sponge kidney 2. Uremic medullary cystic disease D. Simple renal cysts E. Multilocular renal cysts F. Calyceal diverticula G. Miscellaneous cysts of renal origin H. Cysts of other than nephric origin
kidneys
.-
ELKIN
Type
I.
Type
II.
Type
I II.
Type
IV.
of Cystic Diseases of the Kidney From Grossman et al.)
Contrast medium in dilated collecting tubules A. Polycystic kidneys of the newborn B. Medullary sponge kidney C. Renal tubular ectasia with congenital hepatic fibrosis Nonfunction throughout or in part of kidney; contour changes in renal outline and collecting system A. Multicystic kidney B. Hypoplastic cystic kidney C. Multilocular cysts D. Simple cysts E. Uremic medullary cystic disease Deformity of renal pelvis and calyces by cysts intermixed with normally functioning tissue A. Adult polycystic kidneys B. Tuberous sclerosis Small cortical and/or medullary cysts secondary to distal urinary tract obstruction A. Posterior urethral valves B. Other obstructions in urethra
RENAL
CYSTIC
101
DISEASE
organized dysplastic multicystic kidney with the kidney containing simple cysts is an organogenesis morass. Tuberous sclerosis is included in Type III along with adult polycystic kidneys because of possible urographic similarities. However, it does not seem reasonable to introduce the angiomyolipomas of tuberous sclerosis into a classification of cysts. Cysts can occur in tuberous sclerosis but these are usually not similar to those of polycystic kidneys. CLASSIFICATION
USED
IN THIS
SEMINAR
In 1969, Elkin and Bernstein’ proposed a classification of cystic disease of the kidney, drawn in part from previous classifications.2-6 Its aims included: (1) group individually the well accepted entities, such as dysplasia and polycystic disease; (2) group anatomically (cortex or medulla) those entities with questionable pathogenesis; (3) group the remaining unusual intrarenal cysts under “miscellaneous”; (4) separate out the extraparenchymal renal cysts. It was hoped that this classification could be kept simple and still be of value to the radiologist. It was also hoped that the classification would promote agreement on terminology. It is a modification of this classification (Table 4) which is used as the basic configuration of this issue of Seminarsin Roentgenology. The classification still suffers from lumping together conditions with little or no clinical relationships.
Questions There still is no completely satisfactory classification of cystic diseases of the kidney since there is as yet no firm basis for categorization. Some of the entities are definitely of genetic nature; some are probably acquired in utero; some are acquired at different stages of postnatal life. In most types of renal cystic disease there is little inkling as to mechanisms of development. It is improper to categorize all cysts of the kidney as forms of polycystic disease. Among the many questions still to be answered in respect to renal cystic diseases, there are a few of special interest. Are the changes of the multicystic kidney due to in utero ureteral obstruction? Multicystic kidney is associated with atresia or stenosis of its ureter; possibly the renal abnormality is secondary to the ureteral obstruction in the embryo or fetus. Dr. Felson’s article deals with this mechanism in detail. Does focal multicystic kidney occur? The entity of multicystic kidney has been described as in-
Table
4. Classification of Cystic Diseases of the Kidney (Modified From Elkin and Bernstein)
I. Renal dysplasia A. Multicystic kidney B. Focal and segmental dysplasia C. Multiple cysts associated with lower urinary tract obstruction D. Hereditary and familial cystic dysplasia I I. Polycystic disease A. Polycystic disease of the young 1. Polycystic disease of the newborn 2. Polycystic disease of childhood B. Adult type polycystic disease I I I. Cortical cysts A. Trisomy syndromes B. Tuberous sclerosis C. Simple cyst (solitary or multiple; unilateral or bilateral) D. Multilocular cyst IV. Medullary cysts A. Medullary sponge kidney B. Medullary cystic disease (uremic) C. Medullary necrosis D. Pyelogenic cyst V. Miscellaneous intrarenal cysts A. Inflammatory (tuberculosis, calculus disease, echinococcus disease) B. Neoplastic (cystic degeneration of neoplasm) C. Traumatic (intrarenal hematoma) VI. Extraparenchymal cyst A. Parapelvic cyst B. Perinephric cyst
volving the entire kidney, unilateral or bilateral. There have been occasional reports of involvement confined to one subdivision of a duplicate kidney, with atresia or stenosis of the ureter draining it. This is still consistent with an obstructive pathogenesis for multicystic kidney. Focal involvement in a kidney with a normal renal pelvis and ureter would be difficult to explain by an obstructive mechanism unless one were to consider focal zones of obstruction in the infundibular-calyceal system. Does infantile polycystic renal disease always lead to death in the neonatal period? We have had one documented exception. This neonate had high-degree renal failure, symmetrically enlarged kidneys and heterogenous nephrogram typical of multiple cysts. At exploratory laparotomy, the kidneys had the characteristic gross appearance of infantile polycystic disease. Yet this child has survived for over 3 yr, the kidneys are now normal in size, and the BUN only moderately elevated. Is adult polycystic kidney a delayed form of infantile polycystic kidney, or are the two completely unrelated? Does there exist a mild form of
102
infantile polycystic kidney, in which the cysts are too small and too few to produce clinically detectable kidney abnormalities, and from which later in life (with growth of the cysts at varying rates and the development of additional cysts) the picture of adult polycystic kidney evolves? There is no evidence for this. The weight of opinion favors the view that there is no relationship between the two entities. How good are the radiologic criteria for the diagnosis of adult polycystic kidneys? The disease may progress asymmetrically; so the kidneys need not be equally involved. In fact, one kidney may be severely involved in characteristic fashion, and the other appear normal. A patient with multiple simple cysts in one kidney may present with the same urographic findings. Similarly, multiple simple cysts of both kidneys may show a urographic appearance similar to that of polycystic kidneys with bilateral changes. Even the pathologist may have difficulty in this regard. An angiographic sign has been used to make this differentiation. In the polycystic kidney, the renal contour and pelvicalyceal deformities are due to the many large cysts. The nephrogram of those portions of the cortex not involved by large cysts appears heterogenous because it is peppered with
MILTON
ELKIN
the lucencies of the small cysts. The kidney with multiple simple cysts shows a normal, homogeneous nephrogram between the cysts. However, the small cysts of polycystic kidney may be too small or too sparse to be discerned. To my knowledge, serial angiographic studies have not been done on a patient before the development of the typical urographic picture of polycystic kidneys. It is an intriguing conjecture that early in life some of these individuals may show a normal urographic and angiographic appearance. REFERENCES 1. Elkin M, Bernstein J: Cystic disease of the kidneyradiological and pathological considerations. Clin Radio1 20:65-82, 1969 2. Emmett JL, Witten DM: Clinical Urography, An Atlas and Textbook of Roentgenologic Diagnosis (ed 3). Philadelphia, WB Saunders, 1971, pp 931-1045 3. Gleason DC, McAlister WH, Kissane J: Cystic disease of the kidneys in children. Am J Roentgen01 100: 135146, 1967 4. Grossman H, Winchester PH, Chisari FV: Roentgenographic classification of renal cystic disease. Am J Roentgen01 104: 319-331, 1968 5. Osathanondh V, Potter EL: Pathogenesis of polycystic kidneys. Arch Path01 77:459-465, 5 10-5 12, 1964 6. Spence HN, Baird SS, Ware EW Jr: Cystic disorders of the kidney. Classification, diagnosis, treatment. JAMA 163: 1466-1412, 1957