Introduction

Developmental variations and anomalies of the kidneys are frequent and do not tend to decrease. Urinary tract anomalies should be detected early in childhood to prevent irreversible complications and diseases such as chronic pyelonephritis, urolithiasis, hydronephrosis etc. [1]. Renal function depends on the function of the renal calyces and pelvis [2]. Knowledge of renal excretory anatomy is important for diagnostic and urological procedures [3]. Anomalies of the pelvicalyceal system can be mistaken for early manifestations of various diseases of the urinary system. Surgical approach often depend on the type of structure of the collecting system of the kidney [3, 4].

There are multiple studies about the developmental variations of the arterial and venous system of the kidneys. However, the description of developmental variations of the excretory system are not abundantly present in the literature. The current study describes some of the anatomical features of the renal pelvis and calyces important in clinical practice.

Material and Methods

The structure of the renal excretory system was studied by means of macroscopic dissection on 90 kidneys donated to the department of human anatomy, of which there were 54 male kidneys and 36 female kidneys. The organs were fixed in a 10% formalin solution for 48 h and then carefully dissected. All measurements were carefully documented and the obtained material was classified according to the studies of M. E. Mebel (1957) (table 1) [4].

The study was conducted according to the ethical laws of the institution and was approved by the ethical commission of State University of Medicine and Pharmacy N.Testemitanu (19.08.2018 nr. 80). The data obtained were analyzed by means of descriptive statistics, correlation was assessed by Spearman’s analysis. A p value of less than 0.05 was considered statistically significant. The age groups of the patients were classified depending of sex (females: VII – 16-20 years, VIII₁ – 21-35 years, VIII₂ – 36-55 years, IX – 56-74 years, X – 75-90 years and males: VII – 17-21 years, VIII₁ – 22-35 years, VIII₂ – 36-60 years, IX – 61-74 years, X –75-90 years).

Results

Males usually had 2-3 large calyx (Table 2, 44 specimens – 81.48%). Four calyces were encountered in 18.52% (10 specimens). Women (Table 3) were more likely to have 3 large calyces, accounting for 61.11% of cases (22 specimens). Less often they had 2 large calyces – 6 specimens (16.67%) and 4 calyces – 6 specimens (11.11% of cases).

The sizes of the renal calyces depending on their number is present in table 4 and 5

Pearson correlation analysis demonstrated that calyces’ lengths correlated best when there were two calyces (r=0.51; p<0.001). When the number of calyces increases, this correlation decreased and when there were four of them – disappeared. At the same time, the length of the calyces decreased with an increase in their number (r=0.37; p=0.012).

Intrarenal pelvis (type I) when the pelvis is completely located inside the sinus, closed by the parenchyma was encountered in 45 specimens, which corresponds to 50% of cases (Figure 1). The extrarenal pelvis that is located outside the sinus and is not covered by the renal parenchyma was encountered in 9 specimens (10% of cases, Figure 2)

Fig. 1: Intrarenal type of pelvis. 1 - renal pelvis; 2 - large calyx; 3 - pyramids of Malpighi (medulla); 4 - cortical substance.

Fig. 2: Extrarenal type of pelvis. 1 - pelvis; 2 - large calyx; 3 - pyramids of Malpighi (medulla); 4 - cortical substance.

Extrarenal type of pelvis with an open posterior surface (Fig. 3), when, the posterior surface of the pelvis is free from the parenchyma and the anterior one is covered by the groove of the kidney was encountered in 18 specimens – 20% of cases. The mixed type, in which the pelvis is located partly inside the sinus, partly outside of it, (Fig. 4) was encountered in 16 specimens, which corresponded to 17.78% of cases. A special type of pelvis, when the pelvis as such is anatomically absent, and two elongated large calyces, connect and form the ureter was found in 2 cases (2.22%, Fig. 5).

Fig. 3: Extrarenal type of pelvis with an open posterior surface. 1 - kidney parenchyma; 2 - renal pelvis; 3 - inferior vena cava; 4 - abdominal part of the aorta.

Fig. 4: Mixed type of pelvis. 1 - kidney parenchyma; 2 - renal pelvis; 3 - inferior vena cava; 4 - abdominal part of the aorta.

Fig. 5: A special type of pelvis. 1 - ureter; 2 - upper large calyx; 3 - lower large calyx; 4 - medulla; 5 - cortical layer.

Discussion

The calyces, pelvis, and ureter make up the macroscopically visible part of the renal excretory tract. According to the literature there are embryonic, fetal and mature forms of the excretory tree.

One of the first classifications was proposed by Legueu (1891), who divided the pelvis into ampullar and dendritic forms [5]. Later, multiple variants of this classification were proposed, highlighting the ampullar, branched and transitional or mixed types [4]. There were also proposals to classify the pelvis into intrarenal, extrarenal, and borderline [6]. It is worth noting that quite often the same anatomical type was given different names by different authors. M.E. Mebel (1957) proposed to divided the pelvis into intrarenal, extrarenal, extrarenal with an open posterior surface, mixed and a special type (when the pelvis is absent). It must be pointed out that in all existing classifications we are talking mainly about the structure of the renal pelvis, while the pelvicalyceal system is overlooked. The pelvis and calyces, both anatomically and functionally are inseparable from each other and represent a single whole. Mebel's classification was one of the first to take into account the structure of the pelvis based on their clinical significance for urology [4].

An intrarenal pelvis (type I) when the pelvis is completely located inside the sinus, closed by the parenchyma was encountered in 50% of cases, while other authors report this type in 33% of cases [4, 7]. The extrarenal pelvis (type II) that is located outside the sinus and is not covered by the renal parenchyma was encountered in 10% of cases, while in literature, this type is seen in 21% of cases [4]. In type III the posterior surface of the pelvis is free from the parenchyma, and the anterior one is covered by a groove of the kidney. This type of pelvis was seen in 20% of cases, while in the literature can be observed in 17% of cases [4]. The mixed type (type IV), in which the pelvis is located partly inside the sinus, partly outside it, was seen in 17.78% and other studies report that it is encountered in 28% of cases [4]. A special type of pelvis (type V), when the pelvis as such is anatomically absent, and two elongated large calyces connect and form the ureter was encountered in 2% of cases, while according to the literature, it occurs in 1% of cases [4].

An example of the variety of shapes and the number of large calyces is present in figure 6. It should be noted that the anatomy of the pelvis is important in urology. The worst prognosis is for stones that are in all calyces or middle and bottom ones. The most favorable stones are found in only one calyx, predominantly in the upper or middle [8]. Another important factor is the size and shape of the pelvis. A narrow pelvis occurs in approximately 48.5% of patients, making it difficult to pass stones [9]. Finally, it is important to take into account the position, angle, distance between the calyces during urological procedures [10]. According to the literature the dendritic pelvis was encountered in newborns and infants in 70% of cases. The ampullar variant of the structure of the renal pelvis was observed in newborns in 5% of cases, in infants – in 13% of cases, in children under 14 years of age – in 15% of cases. A mixed type of structure of the renal pelvis was observed in newborns in 5% of cases, in infants - in 17% of cases, in children under 14 years of age - in 15% of cases [11]. This underlines the fact that the anatomy of the excretory system develops over time.

The morphology of the pelvis depends on the number of calyces. A number of authors believe that in most cases there are 2-3 large calyces in the kidney. The situation is more complicated with small calyces.

According to different researchers, the number of small calyces varies from 5 to 20, but usually 8-9 according to R. G. Harrison (1972) and 7-8 according to M. Dyson (1995) and W. H. Hollonshead (1975) [12-14]. F. T. Graves (1986) described the pelvicalyceal arrangement in two primary and two transitional types based on the shape of the pelvis and the visibility of the calyces. Type A is an Y-shape, type B is an inverted T, type C is a ball, and type D is an inverted bagpipe [9]. F. J. Sampaio (1993) classified the anatomy of the pelvicalyceal system into two large groups A and B, which are divided into subgroups: A-I, A-II, B-I, B-II. In group A-I, the large calyces from the lower and upper poles represent the primary division of the pelvis, and the middle zone is occupied by the small calyx. In A-II these calyces cross. In B-I – a group of small calyces drain into the middle large calyx. In B-II, many small calyxes are connected to the pelvis at different angles [15].

The classification of the pelvicalyceal system into triangular (three calyces) in 51-54% of cases, multi-cup in 12-15% of cases, Y-shaped (two calyces) in 22-30% of cases and an unusual shape in 4-12% of cases is widespread [16, 17]. This can be different in children. Thus, a triangular (three) shape occurs in 36-40% of cases, a multicalyceal shape – in 30-34% of cases, a Y-shaped shape – in 20-24% of cases, and an unusual shape – in 6-10% of cases [17, 18].

Similarly, several authors divide the pyelocaliceal system into 2 major calyxes in 50-65% of cases, three major calyces in 30-32% of cases, and one major calyx in 3-10% of cases [7, 19]. In rare cases, large calyces may be absent: bilaterally in 5% of cases and unilaterally in 5% of cases [7]. H. Fine and E. N. Keen (1966) also divide the pelvicalyceal system into 4 types, but depending on the area that is drained by the calyces. Type A (38%) – upper and lower large calyces, no middle calyces. Type B (33%) – upper and lower large calyces, small calyces in the middle. Type C (26%) – upper, middle and lower large calyx. Type D (3%) – absence of large calyces [20]. Some of these classifications are similar and their comparison is presented in Table 6.

Finally, one of the latest proposed classifications is the classification of the author R. Takazava (2018). The classification is presented as type I – one pelvis (58%) and type II –bifurcated pelvis (42%). Type II was subdivided into IIa – standard type (43%), IIb – wide type (4%), IIc – narrow type (11%). The subclassification was based on the ratio of the width of the pelvis to the pelvic-ureteral anastomosis [21]. These classifications are presented by us in the form of a graphical adaptation in Figure 6.

Developmental variations of the renal vascular and venous systems are common and can often be overlooked in clinical practice [22, 23, 24]. This affirmation is also similar to renal excretory system.

Fig. 6: Classifications of the most common types of pelvicalyceal system.

Conclusions

Developmental variations of the renal excretory system are frequent. There are multiple classifications that can be used in clinical practice depending on the surgical or endoscopic procedure. Most of the available classifications aim at assessment of the drainage area of the calyces and anatomical structure of the pelvis.

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