2. Gross and Laparoscopic Anatomy of the Lower Tract and Pelvis
KeywordsPelvic topographyPelvic organsPelvic fasciaPelvic vascularisationPeriprostatic nerve routesPelvic floor (muscles)Inguinal canalAnterior abdominal wallEmbryology
An overview of the gross and laparoscopic anatomy of the lower urinary tract should summarize both long-standing anatomic knowledge and current scientific findings. In few fields has the anatomic understanding grown as much as urology, especially concerning anatomy of the lower urinary tract. Whereas the gross anatomy is already well known, now research is increasingly contributing to our understanding of the microscopic level. This concerns especially the detailed anatomy and topography of the sphincter mechanism of the urinary bladder, the routing and function of the neural structures in the pelvis and, for example, the anatomic structure of the pelvic floor. The transmission of these new findings in combination with traditional anatomic knowledge into urological practice, including the growing field of laparoscopic surgery, is essential to maintain and improve the success of treatments for our patients. The following chapter gives a clear, detailed and informative summary of the anatomy of the lower urinary tract, especially considering of laparoscopic and endoscopic surgery.
The History of the Study of the Urological Anatomy
The historiography of urology goes back to 1000 BC in Egypt. The first description of a bladder catheter made of bronze dates to this time, and bladder stone surgery also seems to have been practiced. The prostate was first described by Herophilus of Chalcedon in 300 BC. Human cadaver sections enabled this first glimpse.
After the widespread rejection of anatomical studies up to the Middle Ages, detailed descriptions of human anatomy began to emerge again with the work of Leonardo da Vinci (1452–1519), Andreas Vesalius (1514–1564) from Brussels and their successor Eustachi (1500–1574). The anatomy of the urogenital tract was mainly revealed by Étienne de la Rivière of Paris with the description of the seminal vesicles, Marcellus Malpighi (1628–1694) with the exploration of renal functioning and Lorenzo Bellini (1643–1704) with the identification of the renal tubuli. The progress of microscopic examinations further advanced the basic anatomical knowledge. In 1684, Mery described the existence of the bulbourethral glands, which was later attributed to Cowper.
The founder of the study of the pathology of the urogenital tract was Giovanni Battista Morgagni (1682–1771) with his work “De sedibus et causis morborum.” Giovanni Battista Morgagni is considered the first to describe prostatic hyperplasia.
One of the milestones in urology—urological endoscopy—goes back to Phillip Bozzini of Frankfurt who invented the first endoscope using candlelight in 1806. This made possible the exploration of the internal anatomical details of a living individual .
Topographic Anatomy of the Anterior Abdominal Wall
Five tissue folds subdivide the anterior abdominal wall. The former embryonic urachus forms the median umbilical ligament between the urinary bladder and the umbilicus. On both sides lateral to the median umbilical ligament, the remnants of the fetal umbilical arteries shape the medial umbilical ligaments/folds—the space in between is called the supravesical fossa. During cystectomy, the medial umbilical ligaments are the main structures to identify and control the superior vesical pedicle including the superior vesical artery. The inferior epigastric vessels underlie the lateral umbilical ligaments/folds. These structures have important significance regarding hernia classification. Medial to the lateral umbilical fold, the medial inguinal fossa represents the passage of direct inguinal hernias. The lateral inguinal fossa corresponds to the deep inguinal ring—the entry to the inguinal canal. An indirect inguinal hernia accompanies the components of the spermatic cord through the inguinal canal into the scrotum. In paediatric urology the Prentiss maneuver requires comprehensive knowledge of the inguinal canal and the course of inferior epigastric vessels to fascilitate adequate orchidopexy in boys with short spermatic cord.
A plain promontorium and wide-open iliac wings characterize the female pelvic bone. The peritoneal pelvic cavity harbours the urinary bladder, the ureters, the uterus, the vagina, the ovaries, the Fallopian tubes and the rectum. The uterus, in between the urinary bladder and the rectum, leads to varying peritoneal conditions, starting from the anterior abdominal wall. The parietal peritoneum covers approximately the upper half of the urinary bladder, the uterus, the adnexa and the anterior wall of the rectum. Thereby the parietal peritoneum forms two parts of the abdominal cavity: the rectouterine excavation (Douglas’ fold) and the vesicouterine excavation. A vaginal manipulator helps to expose these pelvic spaces during laparoscopic surgery. The peritoneal fold between the uterus/cervix and the pelvic wall is called the ligamentum latum or broad ligament, although these structures lack some of the typical features of a ligament in the anatomical sense. The uterine artery, the uterine venous plexus and parts of the distal third of the ureters are included in the broad ligament. Ovaries and the Fallopian tubes are also joined to the broad ligament by a peritoneal duplication. The ovaries receive their blood supply through the suspensory ligament (often also called infundibulopelvic ligament), and they are connected to the uterus by the (proper) ovarian ligament, which is part of the broad ligament and includes a secondary blood supply called ovarian branches of the uterine artery. At least, the round ligaments represent connections between the deep inguinal rings and the uterine horns. Embryogenetic, the round ligament corresponds to the gubernaculum testis in males.
The pelvic fascia with its parietal and visceral layer covers the borders of the subperitoneal space; the clinical synonym is “endopelvic fascia”. The endopelvic fascia also forms the superior layer of the fascia of the pelvic and urogenital diaphragm. The urinary bladder is attached to the pubic bone/symphysis pubis via the pubovesical ligaments (analogous to the puboprostatic ligaments in male humans, see also below) with lateral connections to the superior layer of the fascia of the pelvic diaphragm. Between the different subperitoneal organs, connective and fatty tissue fills the resulting spaces (presacral, prevesical, paracervical, parametrial). The stability of the uterus and the cervix is guaranteed by the rectouterine (synonym, sacrouterine) ligament and the topography of the other pelvic organs. The cardinal ligaments (synonym, transverse cervical ligaments) on the base of the broad ligament, joining the cervix and the lateral pelvic wall, are not there at birth but are shaped throughout a lifetime by the increasingly compact and strong connective tissue. They increasingly support the topographical position of the cervix [2, 4–6].
In contrast to the female pelvis, in male humans the pelvic bone is narrower and marked by a more protruding promontorium, resulting in a heart-shaped pelvic entry. The pelvis accommodates the urinary bladder, the ureters, the prostate, the seminal vesicles, the deferent ducts and the rectum. The parietal peritoneum also covers the pelvic organs starting from the anterior abdominal wall to the anterior rectal wall. Between the urinary bladder and the rectum, the deepest point of the abdominal cavity forms the rectovesical excavation. On both sides the rectovesical fold confines the excavation and includes the inferior hypogastric plexus. The deferent ducts shape the paravesical fossa by raising a peritoneal fold.
The subperitoneal space in front of and lateral to the urinary bladder is clinically called the cavum retzii. A look at the existing literature concerning the anatomical conditions of the subperitoneal fascias, especially the prostate-surrounding tissue and the formation of the so-called Denonvilliers’ fascia, demonstrates an inconsistent presentation and nomenclature. The following explanations will outline the most usually published anatomical findings and interpretations. The pelvic fascia in males also consists of two parts: a parietal layer, which covers the lateral wall of the pelvis, and a visceral layer covering the pelvic organs. The tendinous arch represents the transition between the parietal and visceral part. Often the visceral layer is clinically indicated as the endopelvic fascia, especially with regard to radical prostatectomy and nerve-sparing procedures. Whether the prostate is actually separated by its own prostatic fascia is under discussion. The absence of the fascia in the apical region of the prostate and the formation of the so-called puboprostatic ligaments by the endopelvic fascia suggest that the visceral layer of the pelvic fascia (=endopelvic fascia) and the fascia of the prostate (periprostatic fascia) correlate. Generally, the periprostatic fascia is described as a multilayered structure, which incorporates neurovascular structures, fatty and fibrous tissue. Interindividual and prostate aspect depended variations (fusion of fascias and prostate capsule) are common, especially with regard to the prostate gland size. The puboprostatic ligaments between the anterior aspect of the prostate and the pubic bone/symphysis pubis do not represent ligamentous structures in the proper sense. In fact, the puboprostatic ligaments are characterized by an aggregation of the pelvic fascia. Possibly muscle fibers (smooth or striated) also contribute to the configuration of the so-called puboprostatic ligaments. Especially in large prostates the correct identification of the dissection plane between the anterior prostate aspect and the puboprostatic ligaments may be difficult.
Similarly, there is a lack of clarity regarding Denonvilliers’ fascia. The anatomical nomenclature utilizes the description rectoprostatic fascia or septum. It represents a membranous separation between the rectum and the prostate/urinary bladder. The fascia emerges from two layers of a peritoneal cul-de-sac, ranging from the deepest point of the rectovesical excavation to the pelvic floor. Recent examinations report the termination of the Denonvilliers’ fascia located at the junction of the prostate and the dorsal (fibrous) part of the rhabdosphincter. In addition, the presence of smooth muscle fibers inside the fascial layers has been reported. There has been extensive discussion about the possibility of surgical separation of both layers during radical prostatectomy. Currently it is evident that microscopically the rectoprostatic fascia consists of two formerly peritoneal layers, which often cannot be divided bluntly. It is assumed that authors illustrating techniques of fascia separation are referencing to the space between Denonvilliers’ fascia and the rectal fascia propria (a part of the visceral layer of the pelvic fascia = endopelvic fascia). Furthermore, adhesions between Denonvilliers’ fascia and the prostatic capsule, primarily at the base of the seminal vesicles, have been identified. These individual findings have to be taken into account for precise retro-prostatic preparation with regard to positive surgical margins during prostatectomy independent of the surgical approach. Periprostatic neural and vascular structures are focused on below [2, 4, 6–16].
Two fibromuscular layers are responsible for the closure of the inferior pelvic aperture: the pelvic diaphragm and the urogenital diaphragm. It has to be emphasized at this point that the term urogenital diaphragm is not part of the anatomic nomenclature. Particularly the presence of a deep transverse perineal muscle was under extensive discussion, whereas recent studies confirm that a deep transverse perineal muscle is present.
The pelvic diaphragm consists of the levator ani muscle and the coccygeus muscle (M. ischiococcygeus). The levator ani muscle in turn consists of the following structures, which are named according to their origins and insertions: the pubococcygeus muscle, iliococcygeus muscle and puborectalis muscle. A superior and inferior fascia covers the levator ani muscle, the superior layer being part of the parietal layer of the pelvic fascia as described above. The levator ani muscle forms an archway-shaped opening for the anus and urethra in males, and the anus, vagina and urethra in females. Interestingly, the levator ani muscle thickness has been reported smaller and the steepness inside the pelvis greater comparing males to females. This might be dedicated to the general form of the bony pelvis and the physical necessities during pregnancy. The innervations for the striated muscles derive principally from the sacral plexus (S3 and S4); some nerve fibers reach the puborectal muscle via the pudendal nerve located in the pudendal canal. Even though the contributions of the shape topography and the contraction of the pelvic diaphragm to anal continence seem to be proven, it is still unclear to what extent these anatomical structures also affect urinary continence. Recent publications have reported the muscular independence between the pelvic diaphragm and the striated external urethral sphincter, whereas an association by connective tissue forming a tendinous connection starting from the inferior part of the external urethral sphincter in females could be demonstrated. Especially because of these interactions, authors suggest the necessity of an intact pelvic diaphragm for urinary continence.
Considering the urogenital diaphragm, the exact anatomical and histomorphological composition is still undefined. Almost all anatomical atlases report that the urogential diaphragm consists of the deep transverse perineal muscle (less developed in females) with a superior and inferior urogenital fascia. Additionally, the superficial transverse perineal muscle inserting at the perineal body (=central tendon of perineum), the striated external urethral sphincter and the surrounding connective tissue complete the traditional view of the urogenital diaphragm. In addition, as described above, smooth muscle fibers originating from the anterior rectal wall integrate into or perforate the urogenital diaphragm (rectourethralis muscle). With reference to the discussions of the existence of a deep transverse perineal muscle, prevailing descriptions in literature and also recent studies of human cadavers report the presence of the deep transvers perineal muscle (Fig. 2.4). The urogenital diaphragm is described as layers of connective tissue embedding the external urethral sphincter in conjunction with the perineal body, the deep transvers perineal muscle, the structures of the inferior pubic bone and the superficial transverse perineal muscle. Whether these findings about the muscular structures of the urogenital diaphragm are possibly due to age-related fatty degeneration of muscular tissue is under discussion and remains unexplained. The main vascular and neural structures—the internal pudendal artery and the pudendal nerve—are located directly below the urogenital diaphragm. The internal pudendal artery is a branch of the internal iliac artery and the pudendal nerve originates from the sacral plexus (S2-4). Both structures surround the sacrospinous ligament and follow the inferior pubic bone inside the pudendal canal as described below. The bulbourethral glands (Cowper’s glands) are located laterally to the membranous urethra at the level of the urogenital diaphragm. They could be visible during deep urethral repair, perineal prostatectomy or gender reassignment surgery. The urethral sphincter mechanism is described out below [2, 6, 13, 17–26].
The urinary bladder is a muscular, distensible organ for urine collection and controlled micturition. Macroscopically the urinary bladder is divided into the apex, corpus, fundus and collum. The average filling volume ranges between 300 and 500 cm3. The mucosa is only loosely adherent to the subjacent muscular layers, except for the trigone where a direct adhesion to the submucosal layers can be found. A fold raised between the obliquely passing ureters on both sides forming the ureteral orifices characterizes the trigone.
The urinary bladder wall is structured as follows: mucosa (transitional cells), submucosa, detrusor muscle (three layers), and surrounding adipose and connective tissue. The detrusor muscle is subdivided into an external and internal longitudinal muscle layer, as well as an interjacent circular layer. The bladder neck, including the trigone, consists of two muscular layers. A specialized circular smooth muscle could not be found. The longitudinal muscle fibers in conjunction with the extending longitudinal fibers of both ureters extend below the bladder neck and reach the muscular layers of the urethra. In male humans these structures reach to the point of the seminal colliculus. Therefore, a closure of the bladder neck to maintain continence, even in case of damage of the rhabdosphincter (e.g. traumatic urethral injury), or to ensure antegrade ejaculation is possible.
The blood supply of the urinary bladder generally derives from two main branches of each of the internal iliac arteries: the superior vesical artery and the inferior vesical artery—often named the superior and inferior vesical pedicle during surgery. The superior vesical artery descends from a common branch with the former umbilical artery, which is part of the medial umbilical ligament (landmark for the superior vesical pedicle during cystectomy). The inferior vesical artery arises from a common branch of the middle rectal artery. Prostatic branches generally derive from the inferior vesical artery. Varying distinct venous plexuses on both sides of the vesical base secure the blood drainage of the urinary bladder. These venous vessels communicate extensively with the prostatic venous plexus in male and the vaginal venous plexus in female humans. Both, the thin venous vessel wall (especially in case of neoplastic vascularization) and the numerous venous interconnections might result in demanding vascular control during radical surgery.