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=Abnormalities in the Form of the Kidney and Ureter Dependent on the Development of the Renal Bud=

By Augustus G. Pohlman, M. D.,

Assistant Professor of Anaiomy, University of Indiana.



The vague references to the embryology made in the usual reports of renal variations are possibly a result of the anatomist not interesting himself sufiiciently in what might be termed " abnormal variations." The eases are written up by the clinicians, who necessarily orient themselves as to the development of the tract from the text-books, as no scheme has as yet been worked out to wliich he may refer in his attempt to classify or account for the interesting and important anomalies of the kidney and ureter. Even the excellent papers of Bachhammer and of Schwarz are lamentably hidden by the obscurity of their titles.

Cases of renal malformation are comparatively rare, but they occur frequently enough to be of interest to the clinician as well as to the anatomist and pathologist. I need only mention the cases of single or misplaced kidney; to the removal of a single unilateral kidney or to the obstruction of the pelvic inlet by a misplaced organ, to illustrate the importance of a thorough knowledge of the anomalies of the urinary tract. It naturally falls upon the shoulders of the anatomist to classify variations, and as these abnormalities are usually the result of faulty development, the basis of the classification must be an embryologic one. That such a classification will include all the anomalies is quite out of the question at present. There will always be a few which cannot be explained, but the number will grow proportionately less as our knowledge of embryology advances. Before the development of the kidney and ureter had been worked out, speculations regarding the origin of abnormalities were far removed from the present accepted ideas.


The first great difficulty met with in the classification of variations from a developmental standpoint is to make the system clear and embracing, and to present the matter in such a form that it may be of use to someone beside the writer. This scheme must be based on facts in the embryology which have been verified personally, and the possible results compared with actual cases. Here again an element of error is met with in that many of the reports are crude and superficial, and too much credence must not be given to them. The exceptions are surprisingly few, and in the field covered in this paper are limited practically to one observer.


The literature referred to is necessarily small, as it was not deemed advisable to conceal any merit the classification might possess by involved references and case citings. Only those anomalies will be considered where both kidneys are present. This subject is excellently covered in the articles by Ballowitz, Moore and Morris, and the possible causes mentioned in my paper in "American Medicine."


I am obliged to set another limit to this paper in that I shall consider only those anomalies which have their origin before the third month. This excludes all congenital abnormalities which depend on the excretory function of the kidney for their manifestation — congenital cystic kidney, congenital hydronephrosis, etc., also the minor variations which are of relatively little importance, as persistent lobulation, etc. In the variations to be mentioned, the kidney is quite normal excepting in its form, and in the form of the pelvis and ureter.


The development of the renal bud has been thoroughly worked out. I will mention the article by Keibel on its earlier stages and that by Hauch on its later development. My own findings have been a confirmation of what has already been demonstrated by many investigators. I will review the embryology of the kidney and ureter by referring to the conditions present in embryos chosen from the Mall collection, from the earliest stage in the development of the tract to an age in which the kidney and ureter have assumed their relatively normal shape and position. The embryos are arranged according to their size, but the figures do not correspond exactly to those mentioned in other articles. It will be remembered that all embryos of the same age are not always of the same size, and allowance must also be made for shrinkage in fixation and embedding.

The embryos are normal and in perfect series. The relations of the kidney and ureter were not only studied from the sections but modeled as well. The review presents the general development of the tract concisely and in sufficient detail for the objects of this article.

In embryo Mall {{CE164}} (3.5 mm.) the cloaca is relatively spacious. The Wolffian duct has not yet reached it and the stage is therefore too young for a study of the urinary tract.

The Wolffian ducts reach the cloaca in a trifle older stage, embryo Mall {{CE76}} (4.5 mm.), and empty well to the front in the lateral wall. There are no signs of the development of the renal buds.

The renal buds appear dorsally on the Wolffian ducts (embryo Mall {{CE80}} — 5.0 mm.). They arise near the cloaca and their blind ends are already capped with renal mesenchyme developed from the surrounding undifferentiated mesodermic tissue.

In embryo Mall {{CE3}} (7.0 mm.) the buds have elongated markedly and the cap of renal mesenchyme to each bud is more distinct and confined to the distal and blindly ending part. One may already separate the developing tract into two segments; the one surrounded by mesenchyme, the kidney; the other from a portion which is not, the ureter. The blind end of the bud shows no signs of dividing. The masses of mesenchyme are placed at the level of the second sacral vertebra.

The blind end of the bud shows the first signs of sprouting into an upper and lower division in embryo Mall {{CE163}} (9.0 mm.). The splitting occurs within the mesenchyme which has increased in size particularly in the vertical diameter.

The definiteness of the upper and lower division is lost in a slightly older stage, embryo Mall {{CE114}} (10.0 mm.), and the condition may more properly be spoken of as a common pelvis to the developing kidney. The two masses of mesenchyme have already assumed the typical bean shape and lie close together with their long axes parallel. The ureter emerges ventrally from each but is still dorsally placed on the Wolffian duct, although the segment of the duct between the cloaca and the ureter has shortened. The upper border of the kidney is at the brim of the pelvis.

Embryo Mall {{CE144}} (14.0 mm.). The kidney lies opposite the third lumbar vertebra and has begun an axial rotation, bringing the hilum toward the middle line. The ureter has also assumed a lateral position on the duct, and the segment of the duct between the ureter and the cloaca has practically disappeared. It may be said that the ureter has a distinct orifice into the urogenital sinus (ventral segment of the cloaca).

In embryo Mall {{CE43}} (16.0 mm.) the ureter has an orifice lateral to the Wolffian duct. The kidney is completely rotated and the hila point toward each other. The upper border of the kidney is opposite the first lumbar vertebra.

The kidnev reaches its normal height about the end of the second month and then receives its blood supply, the vascularization coming directly from the aorta and occasionally from the suprarenal artery. The vessels seem to choose the nearest route and go to the hilum, the branch from the suprarenal sometimes entering the upper pole.

The ureter grows away from the Wolffian duct, embryo Mall {{CE22}} (20.0 mm.) and empties higher and more laterally. Keibel describes a trigone in his embryo Lo (24.0 mm.). The ureter assumes its relatively normal position in the same stage in which the kidney reaches its normal height or about the end of the second month. The two processes are, however, quite distinct. The change in the position of the kidney is due to the development of the distal part of the bud and its surroundings, while the change in the position of the ureter is related to the growth at the lower end of the Wolffian liuct. It is interesting to note that the ureter normally loses its connection with the Wolffian duct before the Mullerian duct reaches the urogenital sinus.


The earlier development of the renal bud may be represented by three simple figures upon which the diagrams used in the later discussion of the variations will be based. Figure 1 represents the first budding from the dorsal side of the Wolffian duct at a short distance from the cloaca; Figure 2, the first subdivision of the bud within the renal mesenchyme (stage of embryo Mall 163) ; and Figure 3 shows Figure 1 (stage of embryo Mall 2) viewed from above. The figures are schematic, but give a fair idea of the relations found in the models of these embryos.


I take the liberty of repeating the tabulation of the steps in the development of the tract as published in " American Medicine : "

I. The renal bud arises dorsally on the Wolffian duct after the duct has reached the cloaca and at a short distance from its entrance.

II. The two buds grow dorsally, lying close together, each being capped with a mass of renal mesenchyme.

III. Each bud divides into an upper and lower sprout at some distance from the Wolffian ducts.

IV. The kidney wanders upward from a position in front of the second sacral vertebra, rotates at the midlumbar region, and finally reaches its normal height about the end of the second month.

V. It becomes vascularized after it has reached its normal height.

VI. The ureter changes its position on the Wolffian duct from dorsal to lateral and comes to empty distinct from it.

VII. The ureter loses its relation to the duct entirely and opens higher and more laterally.

It may appear that something is taken for granted when it is assumed that the iipper and lower sprout of the renal bud found in an embryo of 9.0 mm. are represented in the adult by the upper and lower pelves of the kidney, especially when the division into an upper and lower sprout is replaced in an older stage by a " common pelvis." However, the assumption is a fair one : there are two sprouts, an upper and a lower, and correspondingly two pelves; in doubling of the ureter the ventral ureter always arises from the upper pelvis as would be expected from the development; and finally, this assumption makes it easy to account for the anomalies to be considered later.


This idea that the upper and lower pelves of the kidney are determined in the earlier stages of its embryology, is contrary to the views held by some that the division of the pelvis into an upper and lower segment is due to the development of the renal parenchyma. The formation of the kidney parench}Tna is secondary to the development of the ureter and its derivatives, and the idea that the growth of the kidney mechanically divides the pelvis is not substantiated in the formation of the anomalies nor does it even allow for the persistence of the lobulation normally present in the beef kidney.


It is granted in this article that the kidney is derived from a double anlage, the renal mesenchyme directly dependent on the renal bud, and that the division into an upper and lower pelvis is determined in the early embryology. It is upon these assumptions that I have based a scheme to be followed in the classification of anomalies of the tract.

No one has observed these variations at the time they were forming, and hence the scheme is merely a hypothesis. However, granting that certain changes do occur normally, is not a hypothesis that will account for the variations from this normal, and simplify the complex embryology of the developmental faults, better than no system whatever? Many renal variations are so rare that it is doubtful whether they will ever be observed in the earlier stages. Even some of the more frequent anomalies as doubling of the ureter has been reported but once in young embryos (Soulie). It was my good fortune to find two cases of complete double ureter in two embryos under the third month. One was discovered quite accidentally, and the other was found in working through the Mall collection. Two cases in over sixty embryos studied.


In all the anomalies to be mentioned none are directly pathologic because all the subjects attained an old age or died from causes quite apart from an abnormal kidney. This is no more than natural, for if the kidneys were not normal at birth, the chances for the individual reaching the age of puberty would be small. The variations are therefore only of inteiest from an anatomic point of view and indirectly of importance to the surgeon. The malpositions of the kidney have a greater interest to the clinician and it is my purpose to present that side of the subject at some later date. The clinical aspect is dealt with in a very thorough manner by Morris.


Anomalies of the kidney may be unilateral or bilateral, and for convenience sake the paper may be divided into three sub-headings :

A. Changes in form of the ureter.

B. Changes in form of one kidney.

C. Changes in form involving both kidneys.


Changes in form of the ureter may be present in changes in form of the kidney or they may be found in normal kidneys. The abnormalities of the ureter are dependent on the renal bud, while the anomalous kidneys result from an abnormal development of the renal mesenchyme, again influenced by the renal bud. The term abnormal refers merely to form and not to function.

==A. Variations in the Form of the Ureter and Pelvis==

===A 1. Incomplete Double Ureter===

Should the renal bud divide too early, or the division extend into the ureter segment (see Fig. Al), that splitting found in the ureter itself would remain a permanent one and any variation might exist as a result from an exaggeration of the usual upper and lower pelves to an incomplete reduplication of the ureter. An incomplete double ureter may be defined as two ureters with a common orifice.

The more complete the division of the ureter segment, the more complete the reduplication. The pelves of the kidney would always be distinct, and it is fair to assume that each subpelvis would follow the rule for the usual normal, and divide into an upper and lower segment (to be dealt with later under A 4).


The ureter from the upper pelvis will normally lie ventral to the ureter from the lower one, as will be evident from the diagram. There are exceptions to this which have a slightly different origin and these will be considered under B 2.

Cases of incomplete double ureter are the most frequent of all renal variations, and are met with yearly in almost every dissecting room. I refer the reader to the article of Schwarz, p. 172, for a review of a number of reported cases, and also to the figures in the paper of Hauch.

The rule for incomplete double ureter may be stated as follows: The pelves of the kidney are always distinct, the ventral ureter arises from the upper pelvis and there is one orifice which is usually normally placed. It is important to distinguish the incomplete double ureter from the complete variety, and in the report of cases the distinction is not often made. Fig. A 1 of the plate represents a very common type of this anomaly.

===A 2. Complete Double Ureter===

Should the splitting of the renal bud be so complete that it is affected by the shortening of the segment of the Wolffian duct lying between it and the cloaca, it is possible for each division to acquire a distinct orifice in the duct as is shown in Fig. A 2. This would result in complete double ureter.

The explanation seems a more likelj' one as the complete double ureter conforms to the rules laid down for the incomplete variety. The only differences are found at the bladder end because of the two distinct orifices.

Cases of complete double ureter are rare but the anomaly has been reported quite frequently in the adult. It was my good fortune to discover two cases in embryos under two months old; one in embryo Piper, the property of Professor Franz Keibel under whom I began to study the development of the human urogenital system, and the other, embryo 175 of Professor Mall's collection. I am indebted to both Professor Keibel and to Professor Mall for the loan of the embryos mentioned in this paper, and also to Mr. Max Broedel for extremely useful suggestions regarding the anomalies of the kidney, and the privilege of mentioning one of his own cases.

Embryo Mall 175 (13.0 mm.). This embryo is cut at twenty microns and stained in carmine. It is well preserved and entirely normal. The sex from the histology of the sex gland is male. The epithelium at the urogenital sinus is loosened a little but not sufficiently to interfere with the conformation. A model of the lower ends of the ureters and of the WolfBan duct was made X 50.

The left kidney and ureter are entirely normal. On the right side, the kidney is also normal but the ureter is completely double. The ureter from the upper pelvis is a trifle smaller and lies ventrally to the ureter from the lower pelvis. This relation is maintained until the ureters approach the WolflSan duct when the dorsal ureter swings laterally. The relation at the urogenital sinus from the midline is : Wolfiian duct, ventral ureter and dorsal ureter.

As to the openings in the sinus, it is extremely difficult to say whether all three have a common orifice, or the ureters an orifice distinct from the Wolffian duct, or all three have separate openings. If the usually conceded fate of the lower part of the Wolffian duct is accepted — that it " unfolds " and enters into the formation of the bladder — any one of these possibilities may be held to be the correct one. Personally, I consider the case one of complete reduplication at a stage in which the lateral orifice is just beginning to shift to a higher and more lateral position.

Suffice it to say, that the two ureters change their relation as they approach the urogenital sinus, and that the dorsal ureter (the one from the lower part of the kidney) comes to lie lateral to the ventral ureter. This would probably be the same if the doubling were complete or nearly complete.

It will be noted that the change in position of the ureter from dorsal to lateral is at about the same time that the kidney undergoes axial rotation. Should the processes connected with the change in relation of ureter from a dorsal to a lateral position on the Wolffian duct be in any way connected with the rotation, the place of the crossing of the ureters would not be found at the lower end, and in cases where the kidney does not reach a normal height, where no rotation has taken place, the ureter would be abnormally situated — which is not the case. For these reasons, it is best to ascribe the changes in the position of the ureter to a development of the lower end of the tract and perhaps to the Wolffian duct as well.

Embryo Piper-Keibel (24.0 mm.). The same condition is found at a later stage in the development. The embryo was cut at fifteen microns and also stained in carmine. The sex is male. On the right side, there is a complete double ureter with two well defined orifices in the bladder. The ureters hold the same relation as that described in the Mall embryo and the ventral ureter swings mesial to the dorsal one as they approach the urogenital sinus. Owing to the development of the bladder, the lateral ureter opens higher and more laterally. It was found to lie in the normal position on comparison with the orifice on the other side. The ventral ureter was probably placed in a position of disadvantage for it lay in the path of the resultant of the forces — between the lateral ureter and the Wolffian duct.

I find a reference in an article by Weigert where in speaking about complete double ureter, he says : " In alien Fallen entsprach die tiefere liegende Offnung in der Blase dem Ureter, der vom oberen Nierenbecken kam, die andere dem, der vom unteren entsprang." This agrees perfectly with my findings in the embryos and with the cases cited in the literature, with a single exception. This is a case reported by Hudson, who pictures a specimen of complete double ureter in which the ventral ureter empties higher than the one from the lower part of the kidney. The specimen was drawn after removal from the body, and it would be a most natural proceeding to uncross the ureters.

There is also an exception to the rule that the more ventral ureter comes to lie mesial to the more dorsally placed one, for according to Weigert : " In den anderen vier Fallen fand eine vollkommene Kreuzung statt, indem der vom oberen Nierenbecken kommende Ureter, der bis dahin medial vom anderen Lag, nunmehr an dessen vordere und laterale Seite zu liegen kam, und in dieser Lagenmg bis an die Blase hinanging. Nach der Kreuzung und namentlich in der Nahe der Blase lagen die Ureter sehr dicht bei einander."

Exactly how this is meant is not quite clear to me. It is quite impossible to account for the condition in which the mesial ureter comes to open higher, and I am tempted to await other cases before giving up the idea that the ureter with the higher orifice must lie lateral to the more mesial opening. In a case reported by Hyrtl the orifices are described as lying side by side.

In one of Weigerf s cases, he mentions the relation of the ureter from the lower pelvis as lateral to the one from the upper part of the kidney. The case is also pictured after the removal of the organs from the body and would be quite possible. The other two exceptions will be explained under B3.

The rule for complete double ureter may be stated: that the relations of the two ureters and pelvis are the same as in incomplete reduplication, and the ureter from the upper pelvis has the lower orifice in the bladder and lies somewhere between the higher opening of the dorsal ureter and the opening of the genital duet. The literature is reviewed by Schwarz, p. 175, and a report of twelve cases is found in the article by Weigert. The doubling according to the latter is usually on one side only.

===A 3. Common Pelvis===

Should the division of the renal bud into an upper and lower sprout be suppressed, or should the later stage of common pelvis persist, there would be no involvement of the ureter and the form of the pelvis would not affect the shape of the kidney because that organ would have its normal origin — from one mass of renal mesenchyme. I find such cases cited by Hauch : " Man sieht die dicken plumpen Formen (casts of the pelvis), die sich garnicht in Calyces teilen, sondern einen l^icht konvexen ausseren Eand haben, an welche sie die Fornices fast ohne Calyxbildung aufnehmen" Fig. 31, 33.

This must be considered a persistence of the stage of common pelvis. It is also found in pathologic conditions, and is, according to Broedel, the first sign of a beginning hydronephrosis which mechanically transforms the upper and lower pelvis into a single one. This is entirely in keeping with the view that the division is due to the development of the cortex. That the damming back of the urine may have this effect is perfectly possible, but that the condition mentioned by Hauch is a variation in the development, is also a fact.

The variation is but a slight one and has no clinical importance or particular anatomic significance.

===A 4. Multiple Pelves and Ureters===

The sprouting of the renal bud takes place at the upper and lower poles and the question naturally arises, in case there are two pelves, the one above the other as is normal, does each pelvis divide into an upper and lower subpelvis as is the rule for the adult form? If we represent the state of afilairs in a stage corresponding to an embryo 9 mm. long by a subdivision of the anlage for a doubling of the ureter, one sprout might divide and the other not as shown in Fig. A 4 a., or both might divide as in A 4 b.

In the former condition the lower pelvis would show the normal division in a kidney with complete or incomplete double ureter and two pelves, the upper simple and the lower divided. This I hold to be very imcommon, and know of no case. In the article by Hauch (Fig. 78) there is illustrated the cast of the upper part of the iireter and pelvis of a kidney in which the double subdivision is clearly shown.

The form of the kidney, if it has been developed from one mass of renal mesenchyme, is not affected by abnormalities of the pelvis, and in this I agree with Hauch : " ''Diese aussere Form der Niere hat keine oder nur sehr wenig Bedeutung fur die Form des Nierenbeckens ; ich verglich die Ausgiisse der verschiedenen, oben besprochenen Nieren mit den Abbildungen von deren Ausseren und sah, wie alle die verschiedenen Formen der Pelvis von des ausseren Form der Niere durchaus unabhdngig sind''."

The doubling of the ureter is always in one plane and the parts are arranged from above down. In case an exaggeration of the condition represented in Fig. A 4 b. be found in the adult, it would correspond to the description of that of Eichmond, in which there were four divisions to the pelvis. Four distinct ducts led from either kidnej', and at a point some four inches below the hilum, united into a common pelvis and afterwards were replaced by a normal ureter with normal opening in the bladder. Although the fact was not mentioned, it may be taken for granted that the pelves were distinct and that the rule for incomplete double ureter held. The division in such a marked manner is extremely rare and may be counted the least common of the variations in the form of the ureter.

The anomalies thus far discussed only affect the form of the ureter, and as has been seen, are determined in the early development of the renal bud. All these variations may be present in abnormalities in the form of the kidney with the exception of the common pelvis. In all marked congenital variations in the form of one kidney the uieter is either completely or incompletely doubled.

==B. Variations in the Form of one Kidney==

It is of course understood, that the kidney form varies to some extent as it is moulded more or less to fit in its surroundings, and that these minor differences are not included in the scope of this article. Only those anomalies are to be considered which are directly dependent upon the development of the renal bud and mesenchyme. It was mentioned that as long as the kidney was developed from one secondary anlage, its form would be normal no matter what the abnormality of the ureter. It must be inferred therefore that the kidney may be derived from more than one secondary anlage if anomalies in the form are found.

Should the sprouting of the renal bud begin early, or the division be placed at different points, or the sprouts be more divergent than is usual, each division might stimulate a mass of mesenchyme, and there would be a double secondary anlage for the kidney. These anlages are naturally placed one above the other and might remain distinct as shown in Fig. B 1, or might fuse at an earlier or later date as represented in Fig. B2.

Granting the condition in B 1 persistent, there would be complete doubling of the kidney, two distinct kidneys on one side with complete or incomplete double ureter, and whether the ureter be completely or incompletely double, the form of the kidney would be the same.

===B 1. Free Supernumerary Kidneys===

A case is reported by Thielmann which gives an excellent illustration of doubling of the kidney with incomplete double ureter. The anomaly is described in great detail and I present the essentials which concern us.

The left kidney was normal but a trifle large. The right kidney was smaller, but also normally formed and placed. The third kidney was situated upon the right common iliac artery, was oval in shape, and a little flattened. The ureter from the upper kidney (the right) crossed it ventrally and received the ureter from the lower kidney which ran upward to meet it at an acute angle. The openings of the right and left ureters were apparently normal.

The blood supply of the upper kidneys was usual. The lower kidney received an artery from the aorta which entered ventrally, one from the right common iliac dorsally, and one from the hypogastric at the lower pole. The anomaly was found in a sailor who had never experienced any discomfort, and whose death was in no way connected with the kidney abnormality. The renal substance was normal.






Bn Figs. B and C.

A similar case is reported by Hyrtl with complete double ureter. In both cases the lower organ was misplaced and pointed hilum ventrally.

===B 2. Fused Supernumerary Kidneys===

In case the two masses of mesenchyme fuse, three possible results are evident: (a) that the fusion of the two secondary anlages may be so complete and at such an early date that the two parts may act in the same way that one mass does (A 1 and A 2), the abnormality of the ureter being merely visible from the outside; (b) demarkation between the two may be well developed and the kidney form otherwise normal ; (c) the fusion may occur at such a late date that one part was rotated before the other became fused to it and this relation would necessarily hold in the adult form.

B 2 a. Complete Fusion.

Barlet describes a specimen of supernumerary kidneys in a letter to the Lancet in the following manner : " On examining the kidneys it was found that the subjects possessed three, two on the left side and one on the right. The two on the left side were fused together, one being on top of the other, and externally showed two ureters springing separately along their whole length, opening into the bladder by two distinct orifices, the one being about one-fourth of an inch above the other. On section there was distinct demarkation of the two kidneys which was not visible from the exterior. All three kidneys were normal in appearance and had no connection with the cause of death."

Here is undoubtedly the same condition found in A 2, with both of the sprouts capped by a separate mass of mesenchyme which fused at an early period. It is not mentioned what the relation of the two ureters was, but it is fair to assume that they followed the rule laid down for the complete double ureter. The specimen appeals to me as a strong piece of evidence to disprove the division into an upper and lower pelvis by the growth of the parenchyma.

B 2 c. Fused Supernumerary Kidneys with One Mass Rotated.

In the discussion of the cases with double ureter, mention was made that two specimens had been reported by Weigert where the ureter from the upper pelvis did not occupy a ventral position. In the cases cited he found the upper part of the kidney rotated in the usual waj', the hilum pointing toward the middle line, while the lower part had the hilum ventrally. He does not mention that these were supernumerary organs, and the following is therefore only inferred from like findings to be taken up later.

The two masses of renal mesenchyme, the secondary anlage for the two parts of the kidney, remained separate until one was rotated at the midlumbar region when the lower and non-rotated part was fused to upper. This would present a result which would correspond with the Weigert cases, and account for the exception to the general rule for double ureter.

Cases of supernumerary kidneys are very rare. Hepburn reports a doubling on both sides in pig, and Amick a similar finding in man. There are still other varieties which will be discussed in a later part of the paper.

==C. Changes in Form Involving Both Kidneys==

Thus far only the changes in the form of one kidney have been considered. There are also changes in form which affect both organs, and these are naturally due to a fusion of the two normal masses of renal mesenchyme (Fig. C). It was stated in a very superficial way in the article in "American Medicine " that it might be possible for the two renal buds to lie so closely together that they might be surrounded by one mass of mesenchyme, and that it would be difficult to distinguish this variety from cases of more or less complete fusion. This statement is withdrawn and I do not hold it possible now for two renal buds to stimulate one mass of mesenchyme; there must be two.

The fusion taking place between the masses will, of course, be a permanent one and the condition receives different names, depending on the position and the degree of fusion, but the class as a class is known as the horseshoe kidney. The varieties depend on the manner and degree of fusion.

It was mentioned that the two masses of mesenchyme lie in front of the second sacral vertebra in an embryo of 7.0 mm. (embryo Mall 2) and are at the same level. The renal buds may not lie at the same level and this is due to a slower growth and later date of appearance of one bud as was dealt with in a previous article. I find that one kidney lies a trifle higher than the other in embryo Mall 114, although both organs are still in the true pelvis. Similarh', it is quite possible to conceive that they might lie one above the other or one in front of the other.


C A. Where the masses of mesenchyme are placed at the same level, they may lie :

a. In the same relative position.

b. One ventral to the other.

C B. Where the two masses are placed one above the other :

a. One slightly in advance of the other.

b. The upper pole of one fused to the lower pole of the other.


C A a. Should the two masses of mesenchyme lie in the same relative position and at the same height, three possibilities as to the point of the fusion may be inferred : 1. Fusion at the upper poles. 3. Fusion at the lower poles. 3. Fusion centrally.

C A b. Should the two masses lie one in front of the other, the dorsally placed organ would fuse to the ventral one iu such a manner that the hilum of the former would attach to the dorsum of the latter.

C B a. Should one mass of mesenchyme be placed a trifle higher than the other, the relation would be maintained in the fusion, and if one kidney were displaced, it would be the lower one, as would be dealt with more completely in a later paper.

C B b. Should the fusion occur end-to-end, the displacement, as above, will be found in the lower organ.

C A a 1. Fusion at the Upper Poles.

In this form of horseshoe kidney the concavity is directed downward, and according to Arneill, is the most uncommon variety. The fusion occurs probably before the organs have grown out of the true pelvis, or as soon as a distinct upper and lower pole have been formed to each mass of mesenchyme (9.0 mm.). The ureter system, being developed from the renal bud, is usually quite normal. The arrangement of the parenchyma joining the kidneys is not known, but there is undoubtedly a more or less definite line of demarkation between the two parts. The earlier the date of the fusion the more indefinite this line would be, and in cases of very late fusion, at about the time that the kidney arrived at its normal height, the growing together might be limited to the capsule. As a rule the capsule is common to both organs.

In a specimen placed at my disposal by Mr. Broedel, there is in addition to other abnormalities a horseshoe kidney fused at the upper poles. The case is unique for this variety of kidney in that the fusion is hehmd the aorta. It will be interesting to work out the arterial defect that allowed the developing masses to slip behind the aorta. The suprarenals, strange to say, were also fused. The blood supply to these organs was naturally abnormal.

Fusion at the upper and at the lower poles not infrequently reaches the normal height, and if the growing together is not too marked, the hila may be rotated to the normal position. C A a 2. Fusion at the Lower Poles.

The most common variety of horseshoe kidney is found in the fusion at the lower poles. It probably has its origin at the same time as the preceding form, and why it should be more common is not known. Many cases have been reported, and as it is only necessary to establish a type in this article, I content myself with referring the reader to the work of Morris on the Surgical Diseases of the Ureter and Kidney, Vol. I, p. 56, where an excellent example of this anomaly is pictured.

The specimen mentioned shows a well-marked bridge of renal tissue connecting the two kidneys at the lower poles. Morris states that the ureters usually lie ventral to the connecting bridge but may lie behind it in case the ureters lie behind the bridge of tissue, the fusion will have been a late one — after the kidneys have been rotated.

The case of Nixon is also alluded to where a similar malposition to that described in the Broedel case was found — fusion at the lower poles and the connecting renal substance behind the aorta. The embryologic defect, probably in the arteria sacra media, which allowed this malposition, would be the same in either case, and will be considered in greater detail in a later paper on the malposition of the kidney.

C A a 3. Fusion Centrally.

The central fusion of the two masses of mesenchyme has received the special name of " disc-kidney." The fusion may be so complete that it is difficult to distinguish any line of demarkation between the two kidneys, and the only grosser structure by which the two organs might be identified would be the two ureters opening into the bladder at either side of the middle line.

The case of Haller, pictured in Morris's work, p. 61, is a typical disc-kidney. The organ is situated in the middle line and the two ureters emerge ventrally. A form of fusion which approaches the disc-kidney in its completeness will be mentioned later.

C A b. Fusion of a Ventrally Placed Kidney to a More Dorsal One.

The only possibility which remains under A is that in the dorsal growth of the two buds, one came to lie farther back than the other and that fusion took place in this position.

In a case mentioned by Morris, there is a variety of fusion which does not resemble any form of horseshoe kidney thus far described. " The two kidneys formed an irregularly shaped mass which weighed thirteen ounces, and was lying on the front of the promontory of the sacrum. It was not horseshoe-shaped and the vessels and ureters were arranged most unusually. The central part of the mass was fissured by a sulcus, in wliich the ureter for the left kidney coursed downwards and the vein for the same upwards, passing into the vena cava just above the junction of the two iliacs. In the right lialf of the mass the ureter and vessels, instead of being situated centrally, were on its outer side; the ureter

being in front of the vessels as on the left and as is usual in fused kidneys." " The renal substance, to the naked eye, was healthy."

I think this explanation of the anomaly could be made: That the two masses of mesenchyme were normally placed excepting that one was in front of the other, and that a fusion occurred between the front edge of the dorsal mass (about the hilum) and the touching edge of the ventrally situated mesenchyme. Both organs were in the pelvic inlet and a later rotation, probably a piirely mechanical one to gain room, turned both ureters toward the same side. The one would in this case undergo a normal rotation and the other, one in the opposite direction. In the specimen of two kidneys pictured by Morris, one must have been placed a little in front of the other.

C B a. Fusion of a Lower Kidney to a Higher One.

In all the variations in the form of the two kidneys thus far considered the two organs were placed at the same level. In embryo Mall 114 (10.0 mm.) one kidney was found lying a trifle higher than the other, although both organs were still in the true pelvis. Should a fusion occur the lower kidney would remain in the lower position.

This type of fusion is found in a case of horseshoe kidney placed at my disposal by Dr. W. H. Lewis. The two kidneys lie on the midline and the right organ is a trifle higher than the left. The mass is somewhat irregular, but the two kidneys are well divided by a longitudinal fissure. The ureters emerge ventrally and empty normally in the bladder. The mass was in a low position and lay upon the bifurcation of the aorta.

These minor differences in height are difficult to tell from disc-kidney, but as a rule the two parts are more distinct. When the difference in the height is more marked, and the organs lie above the point of rotation, the lower kidney is usually displaced and crosses to the opposite side — crossed dystopia (see McMurrich's article).

The fusion of a higher kidney to a lower kidney may be any variety from a disc-kidney to an end-to-end fusion which is discussed in the next sub-heading. The blood supply to these organs is more or less abnormal, depending on the degree of the malposition. Normally placed horseshoe kidneys may have a normal blood supply.

C B b. End-to-end Fusion.

In a case reported by Broesicke, two kidneys were fused end-to-end and both organs were placed to the left of the middle line. The arrangement of the ureters was strikingly abnormal. The upper ureter arose from the mesial surface of the mass and the lower one from the lateral side. The openings of the ureters in the bladder were normal. The specimen is one of " sigmoid kidney." Broesicke agrees with Schultze that the anomaly is explained on the basis of the embryology.

Here the two masses of mesenchyme were placed one above the other and fused after the rotation of the upper kidney took place. The case is similar to the variety discussed under B where the upper half of the kidney rotated and then became fused to the lower part.

These end-to-end fusions are all of relatively late stages. Should the two masses fuse at a very early date, there would be difficulty in distinguishing the two kidneys. The mass would be different from the centrally fused horseshoe kidney in that the ureters would be placed one above the other. This form of kidney is reported by Morris and pictured on page 49. The variety is interesting in the discussion of the causes of the rotation.

C C. Fusion of Supernumerary Kidneys of Opposite Sides.

Granting that the doubling of the kidney may be found on one or both sides and that fusion between the masses of mesenchyme on the same and opposite sides may take place, a number of combinations may occur which are represented in the scheme below. Naturally all these cases have not been reported, but this does not preclude the possibility of their being found. It must be remembered that fusion between a normal mass of mesenchyme on one side and two masses on the other may also occur, and the resulting form is easily deduced from the scheme.

In the first series, the upper and lower masses are presented as remaining free :

a. Horseshoe kidney with free supernumerary kidneys below.

b. Horseshoe kidney with free supernumerary kidneys above.

c. Double horseshoe kidney (no cases reported).

In the second series, the upper masses are fused to the lower :

d. Horseshoe kidney with fused supernumerary kidneys below.

e. Horseshoe kidney with fused supernumerary kidneys above.

f. Fusion of all four parts (e and f reported).

In the third series, the organs are placed at different levels :

g. Horseshoe kidney with free supernumerary above and below. 

h. Horseshoe kidney with fused supernumerary above and below, 

i. End-to-end fusion of all four parts (none reported).

C C e. Horseshoe Kidney with Fused Supernumerary Kidneys Above.

A specimen is described by Oleson of four kidneys in a human being. The mass was fused at the lower poles, and on each side there appeared to be a division into two. From the report it is gathered that the ureters were incompletely doubled, and that the author Identified the two supernumerary organs above.

C C f . Fusion of All Four Parts.

Morris pictures an anomalous kidney mass, p. 54, the case of Batallus, which I take to be the fusion of four kidneys. The mass presents " a quadrilateral appearance " and each ureter divides into two. There is, of course, a question as to the definiteness of this statement, but the case seems to conform, and there is no reason why double kidneys on either side should not behave like a central fusion of the disc-kidney variety.


There are some abnormalities which are not included in this paper, and only those have been mentioned which seem to find an explanation in the development of the tract. The embryology of these anomalies is not very complicated when one follows the development closely. The supernumerary kidney, like the double ureter, has a distinct importance in the study of normal embryology, and serves to substantiate the rule which was assumed in the first part of this article that abnormalities in form are dependent on small variations in the development of the renal bud and mesenchyme before the embryo reaches a size of 10.0 mm.


The letters and numbers of the figures in the plate correspond to the numbers and letters in the paper, and to simplify matters, all those which have been reported are marked with an (r). In the schemas of the horseshoe kidneys, the one ureter has been pictured black, and in the supernumerary kidneys the ureters have been omitted and the one side made black; the concave side representing the hilum in each.

==Literature==

Amick, M. C: Four Kidneys. Cincinnati Med. Report, 1871, IV, 551.

Arneill, J. E. : Anomalies of the Kidney. Eef . Handb. Med. Sci., Vol. V, 319.

Bachhammer, J. : Ueber einige seltene Varietaeten des menseh. Koerpers. Arch. f. Anat. u. Phys., 1879, 139.

Ballowitz, Emil : Ueber angeb. einseit. volkommenen Nierenmangel. Virchow^s Archiv, Vol. 141, 309.

Barlet : Double Kidney. Lancet, 1904, 124.

Batallus: (Cited by Morris).

Broesicke: Ein Fall von congenitaler S-formiger Verwachsung beider Nieren. Virchow's Archiv, Vol. 98, 338.

Haller : ( Cited by Morris ) .

Hauch: Ueber die Anatomic u. Entwick. der Nieren. Anat. Hefte, Heft 69, Bd. 22, 2.

Hepburn, David: Abnormal Kidneys from Domestic Pig. Jr. of Anat. and Phys., Vol. 29.

Hudson, L. : Double Ureter. Lancet, 1903, Vol. II, 1006.

Hyrtl, J. : Ein wahrer Een tertius. Oesterreich. med. Wochensch., 1841, 965.

Keibel, Franz. Zur Entwick. des menseh. Urogenitalapparates. Archiv f. Anat. u. Phys., 1896, 55.

McMurrich, J. P. : A case of crossed dystopia of the kidney with fusion. Jr. of Anat. and Phys., Vol. 32, 652.

Moore, F. C. : Unilateral Eenal Aplasia. Jr. of Anat. and Phys., Vol. 33.

Morris, Henry : Surgical Diseases of the Ureter and. Kidney. 2 Vols, 1901.

Nixon: (Cited by Morris).

Oleson, E. B. : Case of Horseshoe Kidney. Annals of Surgery, 1894, 731.

Pohlman, A. G. : Concerning the Embryology of Kidney Anomalies. American Medicine, June 18, 1904.

Eichmond, W. S. : Abnormal Ureters. Jr. of Anat. and Phys., Vol. 19.

Schwarz, C. : Ueber abnorme Ausmundungen der Ureteren und deren chirurgische Behandlung. Beitrage z. klin. Chir., Vol. 15, 159.

Soulie: Le Progres medical, 1895, 382.

Thielmann, C. : Drei Nieren im Leichname eines Menseh. Archiv f. Anat. und Phys., 1835.

Weigert, C. : Uber einige Bildungsfehler der Nieren. Virchow's Archiv, Vol. 70, 490.


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