Notions of Histology, Anatomy, and Physiology of the Upper Urinary Tract






Generalities


The upper urinary tract, composed of the pyelocaliceal system and the ureter, ensures the function of vector of the urine from the kidney to the urinary bladder through peristaltic contractions. Knowing the internal configuration of the upper urinary tract, as well as the topography and the relations of its composing segments, is essential for the proper integration of information provided by endoscopy and fluoroscopic monitoring. Also, adapting the ureteroscopic technique to the micro- and macroscopic anatomical particularities of this segment makes it possible to perform endoscopic interventions with maximum efficiency and safety.





Notions of upper urinary tract histology


The histological structure of the ureter, renal pelvis, and calyces has major implications in the ureteroscopic approach of the upper urinary tract. Lesions in these structures during endoscopic maneuvers are relatively frequent and require adequate knowledge of the histological particularities.


The ureteral wall consists of three layers:




  • tunica adventitia



  • tunica muscularis



  • tunica mucosa



The adventitia, which is the outside layer, is made of elastic connective tissue.


The muscular layer consists of longitudinal and circular smooth muscle fibers. Its abundant vascularization could explain the important bleeding that occurs in case of ureteral perforations.


In the upper 2/3 of the ureter, there are two muscular layers: a superficial one (circular, thin) and a deep one (longitudinal, thick). In the inferior 1/3, a third, external muscular layer with longitudinal fibers is added. These layers are interconnected by muscle fibers exchanged between the adjacent layers. Due to this extensive interconnection, the individual muscle layers do not have a strictly spiral arrangement around the ureter ( ). The density of the muscle fibers in the proximal ureter is reduced. Consequently, the proximal ureteral wall is thinner than the distal one, implying an increased risk of ureteral perforation.


The muscle layer of the uretero-vesical junction consists mainly of longitudinal fibers. The lateral fibers of the external longitudinal layer head toward the ureteral orifice, while the medial ones are intertwined with those from the opposite side, forming the interureteral bar. In this way, the bladder trigone is delimited. The circular layer disappears and its fibers arrange themselves in the form of islands and mix with the fibers of the internal longitudinal layer, forming helicoidal systems. This disposition of the muscular fibers at the level of the uretero-vesical junction plays a very important role in the antireflux mechanism. There are significant structural differences between the structure of the ureteral muscular layer and the vesical one ( ).


The smooth musculature of the ureteral wall plays a major role in the transport of urine. Through peristaltic contractions, the urine is propelled in the form of successive, rhythmical jets with a frequency of 1–4 per minute.


The ureteral mucosa is disposed in longitudinal folds that, on the transversal section, give the ureteral lumen its characteristic stellate aspect. It consists of a pseudostratified epithelium (polymorphic type covering epithelium, urothelium, or transitional epithelium) located on a dense corium, consisting of fibro-elastic connective tissue arranged irregularly. The epithelium is separated from the corium by a basement membrane.


The transitional epithelium represents a particular form of stratified epithelium whose cells present a high degree of plasticity. It has the ability to display its cells on several layers according to the extent of the surface that it must cover at a given moment. Classically, the urothelium has three cellular layers: basal, intermediate, and superficial.


In fact, all the cells of this epithelium reach the basal membrane, while the free surface is reached only by a part of the cells, which have a bulging and vesicular apical pole. The luminal cells of the urothelium are characterized by the presence of a specialized apical membrane, being attached to the ones situated toward the ureteral lumen through a junctional complex. Pluristratified nuclei are observed in hematoxylin-eosin staining. The first layer of cubic-prismatic cells from the basal membrane belongs to the basal or germinating layer. The cells have a polymorphic aspect (polyhedral or fusiform, piriform or “tennis racket” cells), with a poorly represented intercellular junction that allows them to slide. This layer of cells becomes unapparent after the epithelium’s distension.


A layer consisting of flattened cells can be observed on the surface. Each of them may cover one or several cells of the underlying layer (umbrella cells). They contain one to two round nuclei, while the cytoplasm presents, at the level of the free surface under the apical plasma membrane, a condensation (the cuticle) that has the role of sealing the mucosa.


One of the most important features of the urothelium is the increased size of the intercellular compartment.


In the normal upper urinary tract, there are no histological differences between the uretero-pelvic junction and the rest of the upper urinary tract. In case of obstruction, there is an increase in the amount of collagen around the muscle fibers and in the proportion of longitudinal muscle fibers, but with an overall decrease in the amount of muscle tissue.


The pyelocaliceal system has a similar histological structure with the ureter.


The mucosal layer is well defined and thick. The muscularis is relatively thin, composed of oblique fibers separated by connective tissue, without presenting the distinct layers from the ureteral level. In the small calyces, deep longitudinal muscle fibers are described that are inserted at the base of the papillae. Circular muscle fibers, whose contraction has a role in the expulsion of urine from the papillary ducts, also exist at this level.


All calyces and a part of the renal pelvis are surrounded by the renal parenchyma and the renal sinus fat. The adventitia from the distal part of the renal pelvis is continued by the renal capsule.





Descriptive anatomy of the upper urinary tract



The Pyelocaliceal System


The pyelocaliceal system consists of the renal pelvis and calyces. The urine from the collecting ducts (which cross the renal pyramids to open into the papillae) is collected in the small calyces (minor or secondary). At the renal level, there are 8–18 pyramids, but only 7–13 minor calyces, some of the latter having more than one papilla. These calyces converge to form the major calyces, which in turn open into the renal pelvis through the caliceal infundibula. The renal pelvis continues on to the ureter via the uretero-pelvic junction, which is situated at the level of the L1 vertebra.


According to the architecture of the pyelocaliceal system, Sampaio proposed the following classification ( ):



  • 1.

    Group A – the pyelocaliceal system has two main caliceal groups (upper and lower), the mediorenal area being dependent on one of these.



    • a.

      Subgroup A1 – the mediorenal area is drained by secondary calyces, which are dependent on the upper or lower caliceal groups or even on both simultaneously.


    • b.

      Subgroup A2 – the mediorenal area is drained by crossed calyces, some toward the upper caliceal group and others toward the lower one, with a space being delimited between them and the renal pelvis, called the inter-pyelocaliceal space.



  • 2.

    Group B – the mediorenal area is drained independent of the upper and lower caliceal groups.



    • a.

      Subgroup B1 – the mediorenal area is drained by a major caliceal group independent of the upper or lower calyx.


    • b.

      Subgroup B2 – the mediorenal area is drained by 1–4 secondary calyces that open directly into the renal pelvis.




Another classification, proposed by Graves, describes four types of pyelocaliceal systems; two primary and two secondary. Thus, for type A, the upper and lower caliceal infundibula are arranged in the shape of the letter “Y,” merging into an elongated renal pelvis. In type B, the lower calyx continues to the upper one, both merging with the renal pelvis at a 90° angle in the shape of the letter “T.” Type C presents a “balloon”-type renal pelvis, the calyces being short and thick. Type D presents a small, round renal pelvis and prominent calyces with long infundibula. Types A and C are considered to be primary, while types B and D are secondary, probably being intermediate forms.


In 1901, Brodel described a model of a pyelocaliceal system, having the anterior calyces in a position medial to the posterior ones ( ). Subsequently, Hodson also described a model, which mirrors the previously described one having the posterior calyces in a medial position and the anterior ones in a lateralized position ( ). This controversy ended in 1984 when Kaye and Reinke, after computed tomography observations, demonstrated that the Brodel-type kidney is found more often on the right side (69%), while the Hodson type is more frequent on the left side (79%) ( ).


However, in vivo , due to the anterior rotation of the renal hilum, the anterior calyces are situated more laterally than the posterior ones in 74% of cases ( ).


The renal pelvis can be intrasinusal or extrasinusal, having relations anteriorly with the renal vein and four segmental arteries, branches of the renal artery, and posteriorly with the fifth segmental artery.



Vascularization


The pyelocaliceal system’s vascularization is ensured by branches of the superior ureteral artery and of the renal artery. Knowing the distribution of the terminal branches of these arterial sources is essential during intrarenal endoscopic interventions in order to choose the site for safely performing incisions or resections, as well as for evaluating the possibility of different complications.


Sampaio studied the relations between the pyelocaliceal system and the intrarenal arteries and veins, describing a model with very important endoscopic implications ( ).


The upper pole arteries have their origins in the anterior branch of the antero-superior segmental artery. The upper caliceal group has close relations, both on the anterior and on the posterior sides, with segmental or interlobular arteries in 86% of cases, as well as with veins anastomosed into plexuses in 84.6% of cases.


For the mediorenal area, the arteries originate from the anterior branch of the renal artery, keeping a horizontal trajectory at the level of the renal pelvis, in its middle part. The middle calyces have anterior relations with a segmental or infundibular artery in 65% of cases and with a vein in 75% of cases. Posteriorly, at least one middle calyx has close relations with the middle branch of the posterior segmental artery (the retro-pyelic artery), and in 21% of cases with a venous branch tributary to the renal vein.


The arterial sources of the lower pole originate from the anterior branch (62.2%) or posterior branch (37.8%) of the renal artery. The lower calyces present, in all cases, anterior relations with a branch of the inferior or antero-inferior segmental artery, as well as with an intrarenal vein. In 32% of cases, this caliceal group has posterior relations with a branch of the posterior segmental artery, and in 21% of cases with a high caliber branch of the renal vein. Also, Sampaio described a venous ring around the lower secondary caliceal infundibula in an important percentage of cases.


In order to avoid vascular injuries, the incisions performed at the level of the pyelocaliceal system (in the treatment of stenoses or diverticula at this level) must be performed superficially (no deeper than 1–2 mm), over short distances and oriented longitudinally. These incisions should be made especially in the upper and/or lower quadrants and never at the anterior quadrant.


Sampaio reported the presence of an arterial and/or venous vessel in close contact with the uretero-pelvic junction’s anterior side in 65% of cases (in 45% of cases represented by the inferior segmental artery). The posterior side of the uretero-pelvic junction is crossed by a significant caliber artery or vein in 6.2% of cases, while in another 20.5% of cases the ureter is crossed by vessels at 1.5 cm below the junction ( ). Because of these relations, it is recommended to perform endoscopic incisions in the lateral or postero-lateral area of the uretero-pelvic junction, where the risk of intercepting an aberrant crossing vessel is very low.



The Ureter


The ureter, a paired organ, is a muscular duct located entirely retroperitoneal, stretching from the renal pelvis to the urinary bladder. The length of this segment of the upper urinary tract is approximately 22–30 cm, with variations from one individual to another and from one anatomical configuration to another. The right ureter is shorter by approximately 1 cm.


Along the trajectory of this organ, areas with an increased caliber have been described, called ureteral spindles (located in the lumbar and pelvic areas), where the diameter is between 5 mm and 10 mm (12–30 F), as well as narrower areas called straits, where the diameter ranges between 2 mm and 4 mm (6–12 F). Three straits are described as:




  • superior – at the uretero-pelvic junction



  • middle – at the crossing with the iliac vessels



  • distal – at the uretero-vesical junction




Trajectory and Relations


The ureter has a downward inferior and medial trajectory, in the shape of the italic letter “S”, both in the transverse and in the sagittal plane. There are three ureteral inflexions: at the level of the kidney, of the marginal flexure (intersection of the ureter with the terminal line), and of the pelvis. The distance between the ureter and the midline varies as follows: at the upper extremity − 4.5 cm, at the level of the marginal flexure − 3 cm, and at the uretero-vesical junction − 1 cm.


Depending on the relations with the sacrum, some authors describe three parts of the ureter as follows:




  • upper – from the renal pelvis to the upper margin of the sacrum



  • middle – from the upper to the lower margin of the sacrum



  • lower – from the lower margin of the sacrum to the urinary bladder



Another classification divides the ureter into two parts:




  • abdominal – from the renal pelvis to the upper edge of the pelvis



  • pelvic – located entirely in the pelvis



The abdominal ureter includes a longer segment, of 14–16 cm, up to the iliac crest, called the lumbar part, and an iliac segment, at the level of the iliac vessels.


At its origin, the ureter comes into contact with the lower edge of the kidney (a reno-ureteral ligament has even been described), after which it has a trajectory anterior to the psoas muscle, which it accompanies up to the upper strait of the pelvis.


The lumbar part has the following anatomical relations:




  • posterior – the psoas muscle, the lumbar transverse processes (at 1 cm medial to their extremities), and branches of the lumbar plexus (the femoral cutaneous and genito-crural nerves), which explains the irradiation of renal colic pain.



  • anterior – with the parietal peritoneum, to which it is adherent and which separates it on the right side from the duodenum, pancreas, Toldt’s fascia I, ileo-biceco-apendicular artery, and the terminal part of the mesentery; and on the left side, through Toldt’s fascia II, from the superior left colic artery.



  • medial – with the inferior vena cava to the right, and the aorta and the vascular arch of Treitze to the left.



  • lateral – with the lower pole of the kidney, the ascending colon to the right, and the descending colon to the left, as well as with the genital vessels that originate from the abdominal aorta at the level of the L3 vertebra and which crosses the ureter posteriorly.



The iliac part of the abdominal ureter crosses the iliac vessels according to Luschka’s law, at 1.5 cm below the bifurcation of the common iliac artery to the right and at 1.5 cm above this division to the left. Through the posterior parietal peritoneum, it has anterior relations with the terminal segment of the mesentery to the right and with the mesosigmoid and its vessels to the left, the ureter being located at the level of the upper edge of the sigmoid fossa.


The pelvic ureter is located in the extraperitoneal tissue, stretching from the upper strait of the pelvis to the opening into the urinary bladder through the ureteral orifices. It descends toward the posterior and lateral (parietal segment), passing anterior to the hypogastric artery and medial to the obturator artery and nerve. At the level of the ischial spine, it changes direction toward medial and anterior (visceral segment), being crossed anteriorly by the vas deferens in men and by the uterine artery at the base of the broad ligament in women, finally entering the bladder wall (intramural segment). The submucosal trajectory of the ureter is approximately 2 cm long and it ends at the ureteral orifice ( ).



Vascularization and Innervation


The ureter has a complex, segmental vascularization, its various parts being vascularized by nearby vessels.


For the abdominal part, the arterial vascularization is ensured by the superior ureteral artery (originating from the prepyelic artery, a branch of the renal artery) and the middle ureteral artery (a branch of the aorta, of the testicular/ovarian artery, or of the common iliac artery). In the pelvic part, the vascularization is ensured by the inferior ureteral artery (a branch of the superior vesical artery or of the artery of vas deferens in men, respectively of the uterine artery in women). All of these arterial sources present multiple anastomoses, creating a periureteral arterial plexus. In the upper part of the ureter, the arterial sources are arranged medially, while the lower part receives the arterial sources from the lateral. This disposition, as well as the relations of the various ureteral segments, should be considered when performing endoscopic incisions.


The venous blood is drained into vessels corresponding to the arteries, which flow into the inferior cava vein, the iliac veins, and the latero-vesico-genital plexus.


The lymphatic system represents a submucosal network of capillaries, from this level the lymph being drained through collecting trunks toward the para-aortic, lumbar, and iliac lymph nodes.


The innervation of the ureter is provided by nervous threads coming from the renal, testicular (or ovarian), and hypogastric (in the pelvic part) plexuses and which reach the ureter along the blood vessels. The afferent fibers accompany the sympathetic nerves and enter the spinal cord at the first two lumbar segments. In the ureteral wall, there are groups of vegetative cells forming intramural lymph nodes.





The Pyelocaliceal System


The pyelocaliceal system consists of the renal pelvis and calyces. The urine from the collecting ducts (which cross the renal pyramids to open into the papillae) is collected in the small calyces (minor or secondary). At the renal level, there are 8–18 pyramids, but only 7–13 minor calyces, some of the latter having more than one papilla. These calyces converge to form the major calyces, which in turn open into the renal pelvis through the caliceal infundibula. The renal pelvis continues on to the ureter via the uretero-pelvic junction, which is situated at the level of the L1 vertebra.


According to the architecture of the pyelocaliceal system, Sampaio proposed the following classification ( ):



  • 1.

    Group A – the pyelocaliceal system has two main caliceal groups (upper and lower), the mediorenal area being dependent on one of these.



    • a.

      Subgroup A1 – the mediorenal area is drained by secondary calyces, which are dependent on the upper or lower caliceal groups or even on both simultaneously.


    • b.

      Subgroup A2 – the mediorenal area is drained by crossed calyces, some toward the upper caliceal group and others toward the lower one, with a space being delimited between them and the renal pelvis, called the inter-pyelocaliceal space.



  • 2.

    Group B – the mediorenal area is drained independent of the upper and lower caliceal groups.



    • a.

      Subgroup B1 – the mediorenal area is drained by a major caliceal group independent of the upper or lower calyx.


    • b.

      Subgroup B2 – the mediorenal area is drained by 1–4 secondary calyces that open directly into the renal pelvis.




Another classification, proposed by Graves, describes four types of pyelocaliceal systems; two primary and two secondary. Thus, for type A, the upper and lower caliceal infundibula are arranged in the shape of the letter “Y,” merging into an elongated renal pelvis. In type B, the lower calyx continues to the upper one, both merging with the renal pelvis at a 90° angle in the shape of the letter “T.” Type C presents a “balloon”-type renal pelvis, the calyces being short and thick. Type D presents a small, round renal pelvis and prominent calyces with long infundibula. Types A and C are considered to be primary, while types B and D are secondary, probably being intermediate forms.


In 1901, Brodel described a model of a pyelocaliceal system, having the anterior calyces in a position medial to the posterior ones ( ). Subsequently, Hodson also described a model, which mirrors the previously described one having the posterior calyces in a medial position and the anterior ones in a lateralized position ( ). This controversy ended in 1984 when Kaye and Reinke, after computed tomography observations, demonstrated that the Brodel-type kidney is found more often on the right side (69%), while the Hodson type is more frequent on the left side (79%) ( ).


However, in vivo , due to the anterior rotation of the renal hilum, the anterior calyces are situated more laterally than the posterior ones in 74% of cases ( ).


The renal pelvis can be intrasinusal or extrasinusal, having relations anteriorly with the renal vein and four segmental arteries, branches of the renal artery, and posteriorly with the fifth segmental artery.



Vascularization


The pyelocaliceal system’s vascularization is ensured by branches of the superior ureteral artery and of the renal artery. Knowing the distribution of the terminal branches of these arterial sources is essential during intrarenal endoscopic interventions in order to choose the site for safely performing incisions or resections, as well as for evaluating the possibility of different complications.


Sampaio studied the relations between the pyelocaliceal system and the intrarenal arteries and veins, describing a model with very important endoscopic implications ( ).


The upper pole arteries have their origins in the anterior branch of the antero-superior segmental artery. The upper caliceal group has close relations, both on the anterior and on the posterior sides, with segmental or interlobular arteries in 86% of cases, as well as with veins anastomosed into plexuses in 84.6% of cases.


For the mediorenal area, the arteries originate from the anterior branch of the renal artery, keeping a horizontal trajectory at the level of the renal pelvis, in its middle part. The middle calyces have anterior relations with a segmental or infundibular artery in 65% of cases and with a vein in 75% of cases. Posteriorly, at least one middle calyx has close relations with the middle branch of the posterior segmental artery (the retro-pyelic artery), and in 21% of cases with a venous branch tributary to the renal vein.


The arterial sources of the lower pole originate from the anterior branch (62.2%) or posterior branch (37.8%) of the renal artery. The lower calyces present, in all cases, anterior relations with a branch of the inferior or antero-inferior segmental artery, as well as with an intrarenal vein. In 32% of cases, this caliceal group has posterior relations with a branch of the posterior segmental artery, and in 21% of cases with a high caliber branch of the renal vein. Also, Sampaio described a venous ring around the lower secondary caliceal infundibula in an important percentage of cases.


In order to avoid vascular injuries, the incisions performed at the level of the pyelocaliceal system (in the treatment of stenoses or diverticula at this level) must be performed superficially (no deeper than 1–2 mm), over short distances and oriented longitudinally. These incisions should be made especially in the upper and/or lower quadrants and never at the anterior quadrant.


Sampaio reported the presence of an arterial and/or venous vessel in close contact with the uretero-pelvic junction’s anterior side in 65% of cases (in 45% of cases represented by the inferior segmental artery). The posterior side of the uretero-pelvic junction is crossed by a significant caliber artery or vein in 6.2% of cases, while in another 20.5% of cases the ureter is crossed by vessels at 1.5 cm below the junction ( ). Because of these relations, it is recommended to perform endoscopic incisions in the lateral or postero-lateral area of the uretero-pelvic junction, where the risk of intercepting an aberrant crossing vessel is very low.

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Oct 10, 2019 | Posted by in UROLOGY | Comments Off on Notions of Histology, Anatomy, and Physiology of the Upper Urinary Tract
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