Gross morphological study of the renal pelvicalyceal patterns in human cadaveric kidneys.

INTRODUCTION: The knowledge of detailed calyceal anatomy is essential for performing urologic procedures such as percutaneous nephrolithotomy, percutaneous nephrostomy, flexible ureterorenoscopy, endopyelotomy, and retrograde renal surgery. This study was performed to analyze the various patterns of pelvicalyceal system in the South Indian population, and compare these with previously published studies in different populations.
METHODS: The study was conducted in 100 kidney specimens. Morphologically undamaged kidneys belonging to both sexes were removed en bloc from cadavers and autopsy cases of the Departments of Anatomy and Forensic Medicine, respectively. The specimens were carefully dissected, and the percentage of various patterns was compared with previous studies.
RESULTS: The renal pelvis was found to be intrarenal in 79% of the specimens. The most common type of anatomy was a bicalyceal system with two major calyces, one each from the upper and lower poles, with the middle zone drainage dependent on any one or both of them. An interesting and rare variation of extrarenal calyces with the absence of renal pelvis was observed in 1% of the specimens. In addition, the presence of minor calyces opening directly into the renal pelvis was seen in 8% of the specimens.
CONCLUSION: A biclayceal system of drainage with intrarenal pelvis is the most common calyceal pattern in the kidneys. The patterns must be borne in mind while examining a radiological report involving the kidneys.

INTRODUCTION

The kidneys on coronal section have an outer cortex and an inner medulla. Extensions of the cortex centrally as the columns of Bertin separate the medulla into pyramids. The apical portion of the pyramids protruding into the minor calyces is called papilla.[1] The minor calyces unite with their neighbors to form two or possibly three chambers, the major calyces. The major calyces drain into the infundibula.[2] The renal pelvis is formed from the junction of the infundibula. The minor calyces, the major calyces, the infundibula, and the renal pelvis are collectively called intrarenal collecting system.[3] Variations in the gross anatomy of the renal collecting system are probably as numerous as that of fingerprints of individuals.[4] The symmetry of the collecting system in a single individual on both sides is only around 37%.[5] Not only do the number and position of different parts of the collecting system vary between individuals, but also the parts can either be absent or numerous.

The renal pelvis can be classified into various types depending on its shape, position with respect to renal sinus, length, and the pattern of drainage of calyces. Bruce et al.[6] observed the position of renal pelvis as intrarenal, extrarenal, or borderline. Didio[7] found that the renal pelvis can be classified based on length as long and brachy types. This concept was reinforced by Anson and Mcvay[8] and Edwards et al.[9]

Ningthoujam et al.[4] proposed another method of classifying the varying pelvicalyceal patterns. The different groups include multicalyceal, tricalyceal, and bicalyceal types. Those patterns that do not fit into any of the above types are grouped as unclassified type. Graves[10] made a different type of classification of the pelvicalyceal patterns depending on the shape of the renal pelvis along with prominences of the calyces.

Sampaio and Mandarim-De-Lacerda[5] gave a variety of dimensions to the classification of the pelvicalyceal patterns based on a three-dimensional study on polyester endocasts. The knowledge of detailed calyceal anatomy is essential for performing urologic procedures such as percutaneous nephrolithotomy, percutaneous nephrostomy, flexible ureterorenoscopy, endopyelotomy, and retrograde intrarenal surgery. It is also essential for indicating and predicting the outcome of extracorporeal shock wave lithotripsy (ESWL) for treating lower pole nephrolithiasis.

In spite of the numerous practical implications of variations in the pelvicalyceal anatomy for urologists and radiologists, only few studies have detailed the morphology of different patterns. Hence, this study was performed to analyze the patterns of calyceal anatomy.

METHODS

One hundred kidney specimens (52 right and 48 left kidneys) from adult human cadavers of both sexes of the Department of Anatomy and autopsied bodies of the Department of Forensic Medicine were included in the study. Morphologically damaged kidneys were excluded from the study. The study was approved by the Institutional Ethics Committee. The kidneys along with the ureter were dissected and removed, washed thoroughly in running water, and serially numbered from one to hundred. The specimen were preserved in a solution containing 10% formalin and thymol. During dissection, the anterior and posterior walls of the renal sinus were removed piecemeal, and the calyces were dissected by making a clean coronal slice from the lateral margin toward the renal sinus.[11] Then, the specimens were studied for variations in the pelvicalyceal pattern.

The position of renal pelvis with relation to the renal sinus was classified as intrarenal, extrarenal, and borderline according to Bruce et al.[6] classification. The intrarenal type completely lies within the renal sinus and the extrarenal type lies entirely outside it. The borderline type lies partly inside and partly outside the renal sinus. Then, the specimen were categorized according to the classification proposed by Sampaio.[5] Based on Sampaio's[5] classification, the pelvicalyceal patterns are grouped into two types A and B. These are further divided into A1, AII, B1, and BII. In Group A, the kidney is drained by two groups of calyces. These two groups seem to arise as a main division of the renal pelvis from the upper and lower poles, and the middle zone has a drainage system that is dependent on upper or lower group of calyces or both. In Type A1, there are two major calyces, one each from the upper and lower poles, with middle zone drainage dependent on any one or both of them. In Type AII, drainage is similar to Type AI but with crossing calyces in the middle zone. In Type BI, there is a separate calyx draining the middle zone which is not connected to either upper or lower pole calyceal groups. In Type BII, the middle zone is drained by one to four minor calyces that drain directly into the renal pelvis. The specimens were also categorized according to Ningthoujam et al.'s[4] classification.

RESULTS

The following observations were made in relation to renal pelvis and pelvicalyceal patterns.

(a) Position of renal pelvis: The position of renal pelvis varies in relation to renal sinus. In the present study, apart from intrarenal, extrarenal, and borderline positions, there was no demonstrable pelvis in 3% of the specimens. Hence, an additional category of absent pelvis was included in this study [Figure 1]. The percentage of specimens belonging to each category is shown in Table 1.

Figure 1

Different positions of renal pelvis with relation to renal sinus. (a) Intrarenal (b) extrarenal (c) borderline (d) absent

Table 1

Position of renal pelvis*

(b) Pelvicalyceal patterns [Figures 2 and 3]: The frequency of various pelvicalyceal patterns was AI – 38%, AII – 12%, BI – 29%, and BII – 20%. Out of the 100 kidneys, one specimen presented with extrarenal calyces with absent pelvis and the ureter was found arising directly from the calyces [Figure 4]. This cannot be categorized into any of the types described by Sampaio. In addition, the presence of minor calyces draining directly into the renal pelvis was observed in 8% of the specimens in the present study. This pattern is included in Type BII of Sampaio classification [Figure 3a]. All specimen fit into one or the other categories described by Ningthoujam et al.[4], [Figure 5]. The specimen with extrarenal calyces and absent pelvis is grouped under the unclassified type. The percentage of specimens belonging to each group in this classification was: Multicalyceal (23%), tricalyceal (27%), bicalyceal (35%), and unclassified (15%). The Type AI (38%) and bicalyceal pattern (35%) were the most common types observed. The Type AII (12%) and the unclassified patterns (15%) are the least common of all the other types.

Figure 2

Type AI of Sampaio's classification. Type AI – Two major calyces from superior and inferior poles with middle zone drainage dependent into any one of them or both. (a) Middle zone drainage into the upper pole major calyx. (b) Middle zone drainage into lower pole major calyx. (c) Middle zone drainage into both upper and lower pole major calyces

Figure 3

(a) Type AII (b) Type BI (c) BII of Sampaio's classification

Figure 4

Extrarenal calyces with absent pelvis. The ureter arises directly from the union of major calyces

Figure 5

(a) Multicalyceal (b) tricalyceal (c) bicalyceal (d) unclassified types of pattern categorized based on Ningthoujam et al.'s classification

DISCUSSION

The knowledge of pelvicalyceal system gained relevance with the advent of newer and effective treatment modalities and investigative procedures to diagnose pathologies involving kidneys. The availability of literature regarding the percentage of various pelvicalyceal patterns belonging to this subgroup of population is meager. Hence, this study was done to provide anatomical data on the various types of pelvicalyceal patterns in South Indian population. Since the study was conducted in cadaveric kidney specimens, all types of patterns including the crossing calyces pattern are identified which can otherwise be misinterpreted in radiological studies as a single calyx, as they appear to superimpose on each other. Sampaio and Mandarim-De-Lacerda[5] presented the patterns in Brazilian population and Ningthoujam et al.[4] did their analysis in Northeastern population. Thus, the present study offers an insight into the various patterns in South Indian population. The most common position of renal pelvis was found to be intrarenal (79%) in the present study. The frequency of specimens in each category was compared between the two sides. The extrarenal (5%) and absent renal pelvis (3%) were observed only in right-sided specimens in the present study. The incidence of extrarenal pelvis quoted in literature is around 10%.[12] The knowledge of the position of renal pelvis has its own clinical implications. On injection of contrast material, the extrarenal pelvis may become dilated as it is not well supported. The radiologic picture offers a differential diagnosis for hydronephrosis. The embryological basis of such a collecting system is due to branching of the ureteric bud even before it establishes contact with metanephric blastema.[13] The interesting variation of extrarenal calyces[1415] was first described by Eisendrath.[16] A case of extrarenal calyces with absent renal pelvis has hitherto not been reported. In our study, the major calyces united with each other outside the renal sinus, and the ureter was found arising thereafter with no demonstrable renal pelvis [Figure 4]. Such a case may pose difficulty in the treatment of nephrolithiasis, interfering with the fragment clearance following ESWL. It is essential to be aware of this condition when operating on a kidney with distorted calyceal appearance on imaging studies done preoperatively. Thus, injury to the calyces can be prevented in operation on an otherwise normally functioning kidney.[171819]

On grouping the specimens according to Sampaio's[5] classification, the most common type of pelvicalyceal pattern seen was Type AI. The order of frequency of the patterns in the present study is similar to Sampaio's study [Table 2]. Among the 100 specimens, the Type A was predominantly found in right-sided specimens, and left-sided kidneys showed a preponderance for Type B pattern. Since the patterns are amply varied in all the individuals and even in the same individual on both sides, it is difficult to differentiate normal from pathology.

Table 2

Comparison of pelvicalyceal patterns (grouped based on Sampaio's classification)

This grouping is important for clinicians because Type AI patterns with two long major calyces from the upper and lower poles do not allow easy passage of flexible nephroscopes when approached from the poles. In the meantime, the presence of minor calyces opening directly into the renal pelvis shall ease fragment clearance following ESWL in case of nephrolithiasis. The only drawback of grouping the patterns according to Sampaio's classification[5] is that, in the present study, the specimen with extrarenal calyces cannot fit into any of the above categories and hence another method of classifying the patterns as proposed by Ningthoujam et al.[4] is done. The bicalyceal type is the most common type in the present study when compared with Ningthoujam et al.'s[4] study where the multicalyceal pattern was the most common pattern [Table 3]. The difference could be attributed to the difference in population groups in which the study was conducted.

Table 3

Comparison of pelvicalyceal patterns (as proposed by Ningthoujam et al.)

In the past, the treatment for nephrolithiasis included open surgery in contrast to percutaneous procedures done recently.[20] While performing percutaneous procedure, the site of entry into the required location has to be made with adequate knowledge of different patterns of the collecting system. The various percutaneous procedures for treating pathologies involving the kidneys include percutaneous nephrostomy, antegrade pyelography, antegrade stent positioning, percutaneous nephrolithotomy, and ureteric dilatation. All these procedures require positioning of a canula or puncturing via percutaneous approach.[21] These procedures are done under imaging guidance bearing in mind the different patterns of the pelvicalyceal system. The basic rule before gaining access into the pelvicalyceal system is that a direct puncture into the renal pelvis is dangerous because of the risk of laceration and bleeding.[2223] The ideal method is to reach the collecting system via a transparenchymal approach into a suitable calyx and then into the renal pelvis.[9] Percutaneous procedures are associated with less vascular complications. In addition to comparing the specimens according to Sampaio[5] and Ningthoujam et al.'s[4] classification, an attempt was made in the present study to compare the difference in patterns between the two sides, and the position of renal pelvis with reference to the renal sinus was also observed.

CONCLUSIONS

There was no significant difference in the order of frequency of different patterns between two sides, except the preponderance of Type A of Sampaio's classification in right-sided kidneys and Type B pattern in left-sided kidneys. The various patterns including the extrarenal calyces with absent pelvis and the minor calyces opening directly into the renal pelvis must be borne in mind before interpreting the radiological data and analyzing the outcome for a treatment procedure intended to be performed.