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Chapter 23 / Anatomical Considerations 433

433

From: Current Clinical Urology, Urinary Stone Disease:

A Practical Guide to Medical and Surgical Management

Edited by: M. L. Stoller and M. V. Meng © Humana Press Inc., Totowa, NJ

Anatomical Considerations

in Urinary Stone Disease

Louis Eichel, MD and Ralph V. Clayman, MD

CONTENTS

URETHRAL ANATOMY

BLADDER ANATOMY

URETERAL ANATOMY

RENAL ANATOMY

IMPACT OF ANATOMY ON SELECTION OF STONE THERAPY

SUMMARY

REFERENCES

Key Words: Kidney; ureter; calyx; anatomy.

URETHRAL ANATOMY

In the urinary tract, all roads lead to the urethra. An understanding of its anatomy,

in both the male and female, is important for the successful and safe removal of bladder

calculi and for the safe passage of both cystoscopes and ureteroscopes.

The male urethra spans approx 20 cm from the distal meatus to the bladder neck. The

urethral meatus can vary greatly in its diameter but in general is the tightest portion of

the entire urethra. Occasionally it is necessary to manually dilate the urethral meatus

or perform a meatotomy to pass an instrument or to extract a distally lodged stone.

For practical purposes the male urethra is divided into three sections: the pendulous,

membranous, and prostatic urethra. The pendulous urethra encompasses the distal

penile and more proximal bulbar portions of the urethra, which lie within the corpus

spongiosum. The urethra will normally accommodate instruments up to 28 French. As

the penile urethra runs directly into the bulbar urethra, its course curves anteriorly and

enters the membranous urethra. The membranous urethra is intimately surrounded by

the external (voluntary) sphincter. This point of anterior deflection and muscular

434 Eichel and Clayman

based occlusion is a potential site of trauma where false passages can be made poste-

rior; understandably it is the most common point of stricture formation. It is important

for the endoscopist to realize that if a false passage has been made with a catheter or

rigid endoscope, that the flexible endoscope may be most helpful as it can be manipu-

lated such that its tip will hug the anterior portion of the urethra and facilitate passage

of a guide wire or the endoscope itself into the true urethral lumen. When stone passage

is inhibited by short strictures along the course of the urethra, direct vision urethro-

tomy with retrograde manipulation of the stone back into the bladder can usually be

performed followed by cystolitholapaxy. More significant strictures that cannot be

easily dilated may require transvesical extraction of a bladder stone followed by ure-

throplasty (1,2).

The prostatic urethra extends from the male external sphincter in the membranous

urethra to the bladder neck (internal sphincter). Here, the urethral lumen is usually at its

widest. Under certain pathologic circumstances that cause obstruction of the bladder

neck such as prostatic hyperplasia and bladder neck contracture or bladder neck hyper-

trophy, there can be difficulty passing stones out of the bladder or passing an endoscope

into the bladder. Obstruction at this level may require transurethral incision of the pros-

tate or bladder neck.

In females, the urethra is typically 4 cm in length. The female urethra can usually be

dilated to 32 Fr to accommodate endoscopes of varying size and for the removal of

bladder stones up to 9 mm in diameter. In addition, stones can form inside urethral

diverticuli. These are best treated with diverticulectomy and primary repair.

BLADDER ANATOMY

The normal functioning bladder is able to store urine at low pressure and then, in a

coordinated fashion with the urethral sphincters, empty to completion. The majority of

the bladder wall is composed of large bundles of interconnecting smooth muscle fibers

that form a powerful meshwork capable of expansion and contraction depending on the

stage of the voiding cycle. These fibers react primarily to cholinergic input. In contrast,

the smooth muscle configuration of the trigone and bladder neck is more organized and

performs several key functions. The trigonal muscle provides a thick supportive backing

for the ureters, which enter the bladder base posterolaterally and travel medially for 1.5–

2.5 cm to open into the bladder lumen at the trigone. As the ureter passes through the

bladder wall it is compressed and narrowed, which can prevent passage of a stone

antegrade or a ureteroscope retrograde. Difficulties with ureteral access can be encoun-

tered following ureteroneocystotomy (discussed later in this chapter).

The bladder neck is intimately related to the trigone and the two as a unit act to funnel

urine into the urethra during the active phase of micturition. Difficulty with bladder

emptying caused by a neurogenic problem, an obstructive process, or poor detrussor

function may lead to urinary stasis and increase the risk of infection. Stasis and infection

are the two main risk factors for bladder stone formation.

Several other factors can lead to bladder stones. In particular, bladder diverticuli can

be a source of urinary stasis and thereby promote stone formation. Foreign bodies such

as iatrogenically placed sutures, indwelling Foley catheters, and indwelling ureteral

stents can each act as a nidus for vesicolithiasis. Last, in patients who have undergone

bladder augmentation or continent urinary diversion, mucous formation and stasis can

create a lithogenic environment (3).

Chapter 23 / Anatomical Considerations 435

URETERAL ANATOMY

The ureter originates from the renal pelvis and transports urine to the bladder in

peristaltic waves. The length of the ureter varies from 22 to 30 cm (4). Its course runs

from the ureteropelvic junction medially where it travels along the medial border of the

psoas muscle just lateral to the transverse processes of the lumbar vertebrae. In the supine

position, this is an uphill climb as the ureter travels over the sacral promontory. At

the L3-L4 level the ureter is crossed anteriorly by the gonadal vessels. As the ureter

passes over the pelvic brim it crosses directly over the bifurcation of the common iliac

artery and then proceeds downhill hugging the contour of the pelvis just medial to the

internal iliac artery. Once the artery branches, the ureter courses between the inferior

vesical artery inferomedially and the superior vesical artery superolaterally. Just before

its oblique insertion into the bladder base (the ureterovesical junction), the ureter is

coursed anteriorly in males by the vas deferens and in females by the round ligament and

then slightly more caudal, laterally by the obliterated umbilical artery (i.e., the medial

umbilical ligament).

Stones tend to lodge at four common points of narrowing along the course of the

ureter: the ureteropelvic junction, the pelvic brim as the ureter courses over the iliac

vessels, the ureterovesical junction, and the ureteral orifice. Among these, the ure-

terovesical junction is often the narrowest, with a diameter of 2 mm. The combination

of these areas of narrowing and the relatively serpiginous course that the ureter takes

from the kidney to the bladder, can make passage of guide wires or endoscopes within

the ureteral lumen quite challenging. For example, it is sometimes necessary to balloon

dilate the intramural portion of the ureter or the ureterovesical junction in order to allow

passage of a ureteroscope. In addition, when passing a ureteroscope up the ureter over

a guide wire in a supine patient, one must visualize the three dimensional course of the

ureter coursing laterally and downward through the bladder wall and then taking a sharp

turn upward (anteriorly) and medially as the instrument needs to be guided anterior out

of the pelvis and over the iliac vessels. The pulsations of the common iliac artery are

clearly transmitted to the ureter at this point. On occasion, it may be difficult to pass a

semi rigid ureteroscope over the pelvic brim, especially in the male patient. This is a

potential cause of ureteral and/or endoscope damage and can be avoided by changing to

a flexible endoscope. Alternatively, this angulation can be modified in the male by

manually pushing the suspensory ligament of the phallus posterior thereby helping with

the alignment of the urethra toward the ureteral orifice.

The upper ureter can, on occasion, J hook making the passage of a guide wire difficult.

This is more common in elderly patients with ptotic kidneys. A variety of endourological

methods for overcoming this problem have been described; however, the simplest

approach is to place the patient in a steep head down position and proceed to manually

push the kidney upward by pressing upward along the upper quadrant of the abdomen

subcostally (Mertz maneuver) (5).

After summiting the sacral promontory it is a slightly downhill course along the mid

and upper ureter toward the renal pelvis, which usually sits at the level of the second

lumbar vertebral body. However, to traverse the ureteropelvic junction, the endoscope

usually needs to be guided even more posterior.

The anterior-posterior course of the ureter as described above is reversed if the patient

is in the prone position during flexible ureteroscopy. In this position, it is most helpful

to first pass a ureteral access sheath to facilitate passage of the flexible ureteroscope.

436 Eichel and Clayman

RENAL ANATOMY

Kidney Position and External Relationships

The kidneys lie in the retroperitoneum on top of the quadratus lumborum and psoas

muscles. Each kidney has a thin walled fibrous capsule that is intimately adherent to the

parenchyma, which in turn is surrounded by perirenal fat. The perirenal fat is contained

by Gerota’s fascia, which in turn is surrounded by another layer of fat (i.e., the pararenal

fat).

Posteriorly, the superior pole of each kidney rests against the diaphragm and the tips of

the 11th and 12th ribs. Deep to this, the underlying pleura attaches to the 11th rib, which

must be considered when a superior pole percutaneous approach is planned, especially

on the left where the kidney lies higher in the retroperitoneum. The adrenal glands rest

on top of the kidneys medially against the cava on the right and aorta on the left.

The anterior surface of the right kidney is associated with the liver superiorly, the

curve of the duodenum over the midportion and the ascending colon inferior and medi-

ally. On the right side, the colon often covers the lower half of the kidney medially. The

anterior surface of the upper pole of the left kidney is covered by the spleen superiorly

and just the tail of the pancreas medially as well as by, the splenic flexure of the colon;

the anteromedial surface of the entire left kidney is covered by the descending colon. A

retrorenal colon can be seen on either side in 1–10% of percutaneous cases depending

on patient positioning; it is more common when the patient is in the prone position.

However, this condition is usually limited to patients with a markedly redundant colon

or patients with a horseshoe kidney (6). Usually the retrorenal colon covers only the

lateral most portion or upper pole of the kidney.

For anatomic purposes, the kidney can be divided into anterior and posterior seg-

ments. The plane of division for these segments rests 30–50° posterior to the frontal

plane of division for the body as a whole owing to the rotation of the renal axis anteriorly

by the psoas major muscle (Fig. 1) (7). The psoas muscle also defines the axis of the

kidneys in the longitudinal plane so that the upper pole is medial and posterior whereas

the lower pole is more lateral and anterior (6). As such, the distance from skin to collect-

ing system is shortest at the upper pole and greatest at the lower pole of the kidney.

Internal Architecture of the Kidney and Collecting System

The glomeruli, proximal tubules, and distal convoluted tubules rest within the renal

cortex, which is the outer most layer of the renal parenchyma. The loops of Henle and

collecting ducts rest within the renal pyramids, which together comprise the medulla of

the renal parenchyma and rest within the center of the kidney. The renal pyramids are

separated by incursions of cortical tissue called the columns of Bertin. The collecting

ducts within each pyramid cone down to drain into a papilla, which is bordered by the

fornix of a minor calyx, the area surrounding the papilla.

Each kidney typically contains 4–14 minor calyces (mean 8) (6,7). The minor calyces

comprising the middle pole of the kidney tend to drain single papilla (simple calyx)

whereas the polar calyces tend to drain two or three papillae (compound calyx). These

papillae may actually be fused to one another in varying degrees. A minor calyx may

drain directly via an infundibulum into the renal pelvis or several minor calyces, as in

the polar areas, may drain into a major calyx, which in turn drains via a single major

infundibulum into the renal pelvis (Fig. 2).

Chapter 23 / Anatomical Considerations 437

Fig. 2. “Classic” left kidney: compound polar calyces (1); anterior calyces (2, 4, and 6) and

posterior calyces (3, 5, and 7). Used with permission from Reference 7.

Fig. 1. Left kidney viewed from above showing anterior calyces projecting 70° and posterior

calyces 20° from the frontal plane of the kidney, as in a classic Brödel-type kidney. Used with

permission from Reference 7.

438 Eichel and Clayman

Sampaio et al. analyzed 140 endocasts of the pelviocaliceal systems of cadaver kid-

neys and derived from this a descriptive classification system based on polar anatomy

(6). Group A kidneys have pelviocaliceal systems comprised of an upper and a lower

pole system. The middle pole minor calyces drain into one of these two major divisions.

Group B kidneys have pelviocaliceal systems in which the midpole calyceal drainage is

independent of the upper and lower pole collecting systems.

The traditional teaching regarding the correlation between the actual anatomy of the

pelviocaliceal and the appearance of the collecting system on intravenous pyelogra-

phy is that on a standard AP view, the anterior calyces appear to be seen in cross section

laterally and the posterior calices appear to be more medial and are seen from a cuplike

end on point of view. Sampaio et al. studied 40 cadaver kidneys in which retrograde

pyelography was correlated with the actual anatomy of the pelviocaliceal system

derived from endocasts (6). In actuality, this relationship (where the anterior calices

are seen laterally and the posterior calices are seen medially) was only present in

27.8% of the kidneys studied. The posterior calices were more lateral in 19.3% of

cases. The largest proportion of kidneys (52.9%) had a mixed pattern. These findings

underscore the importance of obtaining high quality imaging studies before planning

an operative approach. In the case of IVP or retrograde pyelography this should include

lateral and oblique views.

Assessment of the Lower Pole Infundibulopelvic Angle,

Infundibular Length, Infundibular Width, and Calyceal Pelvic Height

It is widely accepted among endourologists that lower pole calculi have a poor clear-

ance rate compared to stones in other locations following shockwave lithotripsy (SWL;

in our study, lower pole anatomy had no impact on clearance after ureteroscopic litho-

tripsy). The dependent position of the lower pole is thought to play a major role. Other

important anatomical relationships to understand with regard to this phenomenon are the

lower pole infundibulopelvic angle (LIP angle), infundibular length (IL), infundibular

width (IW), and calyceal pelvic height (CPH). Several studies exist in the literature that

either support or refute the importance of these parameters with regard to stone clearance

rates and treatment success rates for lower pole stones. When reviewing studies that use

the LIP angle as a potential indicator of the odds of treatment success, it is important to

remember that the angle can be measured several ways. Figure 3A demonstrates this

point. The measurement is calculated using the angle between the central axis of the

lower pole infundibulum and one of the following: the ureteropelvic axis, the vertical

ureteral axis, or the renal pelvic axis (8–10).

The IL is calculated as the distance from the most distal point at the bottom of the calyx

containing the stone to the midpoint of the lower lip of the renal pelvis (8) (Fig. 3B).

Another similar measurement used to predict odds of stone clearance is

the CPH. This is defined as the distance between the lower lip of the renal pelvis the

lowermost point of the stone containing calyx (11,12) (Fig. 3C). The IW is measured at

the narrowest point along the lower pole infundibular axis (Fig. 3D).

Several studies support the theory that lower pole infundibulopelvic anatomy affects

stone clearance rates. In his original article on this subject, Sampaio et al. studied endo-

casts from the collecting systems of 146 cadaveric kidneys. He found three factors that

may play a role in lower pole stone clearance: the infundibulopelvic angle (clearance of

Chapter 23 / Anatomical Considerations 439

Fig. 3. (A) Different method of determining main axis for measuring lower pole infundibulo-

pelvic angle using vertical ureteral axis (a), ureteropelivic axis (b), and renal pelivic axis (c).

(B) Infundibular length measured as distance from the most distal point at the bottom of calyx

containing stone to mid-point of lower lip of the renal pelvis. (C) The calyceal pelvic height

is measured as the distance between the lower lip of the renal pelvis and the lowermost point

of the stone containing calyx. (D) Infundibular width is measured at the narrowest point along

the lower pole infundibular axis.

440 Eichel and Clayman

74% when the angle is >90° and 26% when the angle is <90°), the infundibular diameter

(60% clearance when it is >4 mm and 40% clearance when it is <4 mm), and the inferior

pole calyceal distribution (57% clearance when the calyces were multiple and simple vs

43% when the calyces were single and of a compound nature) (10). In a follow up

prospective study by Sampaio, 74 patients received SWL for lower pole stones. The

stone clearance rates for patients with an LIP angle greater than vs less than 90° was 75%

vs 23% respectively (13). Another retrospective study by Elbahnasy et al. reported 21

SWL patients and 13 ureteroscopy patients who were treated for lower pole stones. In

the SWL group, the infundibulopelvic angle in the stone free vs residual group was

significantly larger (75° vs 51°). There was no difference, however, in the ureteroscopy

group (56° vs 49°). Furthermore, in the SWL group, the IL was significantly shorter and

the IW greater in the success vs nonsuccess (32 mm vs 38 mm and 9 mm vs 6 mm

respectively). Again, there were no significant differences in the ureteroscopy group.

These findings were supported in a later study comparing treatment of solitary lower

pole stones with SWL, PCNL, and ureteroscopy where SWL was sensitive to lower pole

anatomy but PCNL and ureteroscopy were not (14). In this study, they also found that

having two or more favorable or unfavorable parameters had a much greater effect than

any single parameter alone in terms of clearance. Based on both of these studies, the

authors concluded that patients with lower pole stones 17 mm or less who have favorable

anatomy (LIP angle >70°, IL <3 cm, and IW >5 mm) are excellent candidates for SWL

whereas patients with less favorable anatomy (LIP angle <40°, IL >3 cm, and IW <5mm)

would be better served by ureteroscopy or PCNL. In further support of these findings,

Keeley et al. retrospectively analyzed the records of 116 patients with lower pole stones

between 11 and 20 mm with regard to LIP angle and also found a superior stone free rate

among patients with a more obtuse angle (15). Infundibular diameter and calyceal con-

figuration were not found to be significant factors. In the largest study to date, Poulakis

et al. reviewed lower pole calculi results in 680 patients (701 renal units) treated on a

Piezolith 2500. They, like Elbahnasy, found the critical LIP angle to be 45º. A CPH

greater than 15 mm was also found to be a significant variable. In this series all patients

with residual fragments had inversion therapy, and the average follow up was 26 mo

(16). Interestingly, in another recent study, an infundibular length to diameter ratio of

less than 7 and an infundibular diameter of >4mm with a single minor calyx affected in

multivariate analysis appeared to be predictive of clearance (85% in 63 patients) (17).

Looking at ureteroscopic treatment for lower pole stones, however, although

Elbahnasy et al. did not find the LIP anatomy to be a significant factor, Kumar, Joshi,

and Keeley did find a negative impact of an acute LIP angle on stone free rate (18). Thus,

some degree of controversy continues regarding this matter.

Even more controversy exists regarding the significance of lower pole anatomy itself.

Moody et al. analyzed the 26 patients who underwent SWL from the Lower Pole Study

Group with regard to LIP angle, IW, and IL as measured according to Elbahnasy. No

significant differences in these parameters were seen with regard to stone free rate. In

fact, the only significant factor measured was stone size (mean 9.6 vs 15.3 mm for stone

free vs not stone free) (19). However, these few patients were treated at 18 different

institutions using 5 different machines. In a retrospective study of 108 patients with

lower pole stones, Madbouly et al. also were unable to find any correlation between

lower pole anatomy and stone clearance following SWL (9). In this study the only

significant factor that affected stone clearance was a history of pyelonephritis. However,

again in this study, patients were treated with three different lithotriptors, some patients

Chapter 23 / Anatomical Considerations 441

had multiple lower pole stones, uric acid calculi were included, and over half of the

patients underwent multiple SWL treatments. The diversity of the patient population

could well have contributed to the authors’ inability to identify any significant param-

eters. More recently, an article by Sorenson and Chandhoke reviewed 190 patients

treated on a Doli U/50 with lower pole, single, calcified stones all  2 cm. These authors

found no impact of lower pole anatomy on stone clearance rates. Of note, in this study,

all patients had postoperative inversion therapy.

As such, the impact of lower pole anatomy as measured on the intravenous urogram

remains controversial. Perhaps, all of these patients should be treated by post-SWL

inversion therapy as this maneuver in two separate studies singularly increased the stone

free rate from 3% to 40% in one study and from 23% to 88% in another study (20,21).

In the final analysis, in this day and age, the point of lower pole anatomy may well be

on its way to becoming moot owing to the demise of the IVP. Indeed, the ability to

measure these parameters is becoming increasingly more difficult given that most renal

calculi are being diagnosed now by means of CT scan. The CT scan of the kidneys, in

its current state, precludes the ability to measure infundibular length, width, and angle.

In the future, there may be a resurgence of interest in this topic when 3D reconstruction

of the CT scan becomes more commonplace enabling a more reliable and reproducible

measurement of these various parameters.

Intrarenal Vascular Anatomy

The pioneering work of Brödel (22) and Graves (23) defined the distinct anatomical

segments of the kidney with their individual arterial branches. Although wide variation

exists, the renal arteries, in general, originate from the lateral margin of the aorta just

below the level of the superior mesenteric artery. They course posterior to the renal vein

and branch on the appropriate side of the renal pelvis into an anterior and posterior

division. The posterior branch is the first main branch of the renal artery in 50% of cases

and supplies the posterior middle segment of the kidney. The anterior segment typically

divides into four branches (apical, upper, middle, and lower). Kaye in 1982 described

this relationship as a hand (i.e., the main renal artery) grasping a glass (i.e., the renal

pelvis) with the thumb branching early and coursing posteriorly (i.e., the posterior seg-

mental artery) and the 4 fingers spreading out over the anterior surface of the glass (i.e.,

the apical, upper, middle, and lower segmental arteries) (24). The segmental branches,

in turn, split to form interlobar arteries that wrap around the superior and inferior poles

of the infundibula to form the arcuate arteries. The arcuate arteries, in turn, branch and

run between the renal pyramids and columns of Bertin. Small branches of the arcuate

arteries perforate the renal cortex to supply blood peripherally. Each individual arterial

branch is functionally an end artery and injury to a branch can lead to loss of segmental

function owing to infarction (Figs. 4A and B).

In an effort to characterize the renal vascular anatomy more specifically in the context

of percutaneous renal surgery, Sampaio and coworkers performed three-dimensional

endocasts of renal collecting systems, arteries, and veins in fresh cadavers (25–27). They

also studied the extent of vascular injuries sustained from percutaneous punctures of the

renal collecting system at various locations (28). They discovered that there is a high

likelihood of a significant vascular injury if the collecting system is punctured through

an infundibulum or if the renal pelvis is accessed directly because the larger vessels

surround these structures. Significant vascular injuries were discovered in 67%, 23%,

and 13% of upper pole, middle, and lower pole infundibular punctures respectively.