Principles and Practice of Urogynaecology

Part I

Anatomy and Physiology

© Springer India 2015

A Tamilselvi and Ajay Rane (eds.)Principles and Practice of Urogynaecology10.1007/978-81-322-1692-6_1

1. Current Concepts in Pelvic Anatomy

Arjunan Tamilselvi¹  

(1)

Institute of Reproductive Medicine and Women’s Health, Madras Medical Mission Hospital, Chennai, India

Arjunan Tamilselvi

Email: [email protected]

Introduction

Female pelvic anatomy can be a conceptual challenge. Understanding the anatomy helps in identification, assessment, and management of pelvic floor pathology. To those dealing with disorders of the pelvic floor and to the reconstructive pelvic surgeon, knowledge of the functional anatomy is crucial. Apart from the anatomical dissections, various imaging modalities particularly magnetic resonance imaging (MRI) have helped in appreciating the relationships and supports of the pelvic organs better. Improved understanding of the pelvic anatomy should make it possible to align anatomy with clinical concepts seamlessly.

The pelvic viscera have an integrated anatomical support with each other due to their orientation within the pelvis, and at the same time, they largely function as individual units. The pelvic floor musculature and the pelvic connective tissue (including fascia and ligaments) form the primary support for the pelvic organs with the bony pelvis providing additional support. In general, the normal anatomical supports of the female pelvic viscera play a vital role in the reproductive, storage, and elimination functions of the pelvic organs, apart from trying to maintain them in their normal position.

The aim of this chapter is to describe the topographic or spatial pelvic anatomy, in a practical aspect to help in optimizing the surgical techniques in pelvic surgery. Three different anatomic systems contribute to the support of the pelvic organs – the bony, muscular, and fascial support. The clinically relevant bony, muscular, and fascial supports and the surgically important spaces in the pelvis are described below along with a brief mention of their clinical/surgical relevance. For a more exhaustive anatomy, the reader is referred to anatomy textbooks cited in the reference.

Bony Support

The female bony pelvis provides the essential framework for muscular and fascial supports. It is important in reconstructive pelvic surgery as certain bony landmarks are the surgical reference points for suture placement and for graft anchoring in reconstructive surgery. The (innominate) hip bones (composed of the ilium, ischium, and pubis) articulate with the sacrum at the sacroiliac joint posteriorly and with each other anteriorly at the pubic symphysis. Within the bony pelvis, there are several important landmarks, openings, and spaces which are of clinical relevance.

The anterior projection of the first sacral vertebra, Sacral Promontory, forms the posterior boundary of the plane of the pelvic brim, while the superior aspect of the symphysis pubis and the iliopectineal lines form the anterior and lateral boundaries respectively (Fig. 1.1). Above the plane of the pelvic brim, the prominent projection of the ilium is the anterior superior iliac spine, from which the inguinal ligament stretches up to the pubic tubercle medially. The large femoral neurovascular bundle passes from the abdomen to the thigh midway underneath the inguinal ligament.

Fig. 1.1

Borders of the pelvic brim (Reproduced from: www.​teachmeanatomy.​com; with permission)

Fig. 1.2

Pelvic outlet borders (Reproduced from: www.​teachmeanatomy.​com; with permission)

The pelvic outlet is diamond shaped with the apices defined by bony landmarks – inferior aspect of the symphysis pubis anteriorly, ischial tuberosities laterally, and tip of the coccyx posteriorly. The outlet can be subdivided into the anterior urogenital triangle and the posterior anal triangle. The lateral edges of the anterior triangle are the ischiopubic rami – which have assumed significance in delineating the obturator foramen for graft anchorage (Fig. 1.2).

Obturator Foramen

The obturator foramen is a large oval window, bounded by the superior and inferior pubic ramus, body of the pubis, ischial ramus, and body of the ischium. The obturator membrane covers this opening almost completely except for a small opening in the superolateral portion of the foramen, the obturator canal through which the obturator neurovascular bundle passes from the pelvis to the medial compartment of the thigh. The obturator internus muscle on the inner side of the obturator membrane originates from the bony margin of the obturator foramen and partly from the pelvic side of the obturator membrane. A curvilinear thickening of the parietal fascia overlying the belly of the obturator internus known as the arcus tendineus levator ani (ATLA) extends from the posterior pubic symphysis to the ischial spine. The obturator externus arises from the outer surface of the obturator membrane and from the pubic and ischial rami and from the medial two-third of the obturator membrane, attaching itself to the greater trochanteric fossa of the femur (Fig. 1.3).

Fig. 1.3

Obturator foramen covered with obturator membrane and the location of obturator canal (Reproduced from: www.​teachmeanatomy.​com; with permission)

Applied Anatomy

The potential safety of the obturator foramen with the neurovascular bundle occupying only its superolateral portion, has made it a safe zone for insertion of the trocars in the transobturator mesh anchoring techniques.

The Ischial Spine

The ischial spines are bony prominences projecting from the medial surface of ischium at the anterior border of greater sciatic notch. The sacrospinous ligament (SSL) passes medially and posteriorly from the ischial spine to the lateral aspect of lower portion of the sacrum and coccyx. The sacrotuberous ligament extends from the posterior surface of sacrum to the ischial tuberosity, and this along with the SSL separates the greater sciatic foramen from the lesser sciatic foramen.

Fig. 1.4

Sagittal section of the bony pelvis. ATLA arcus tendineus levator ani, ATFP arcus tendineus fascia pelvis, C-SSL coccygeus–sacrospinous ligament complex

Applied Anatomy

The ischial spines are important surgical reference points for several pelvic structures (Fig. 1.4):

The pelvic ureter usually leaves the pelvic sidewall about 1–2 cm from the ischial spine to pass medially on the pubocervical fascia before entering the bladder.

The pudendal nerve and vessel exit the pelvis through the greater sciatic foramen and course beneath the ischial spine and sacrospinous ligament before reentering the lesser sciatic foramen. Identification of ischial spine is essential when performing sacrospinous fixation and planning suture placement to avoid injury to the pudendal neurovascular bundle.

The arcus tendineus fascia pelvis (ATFP) and arcus tendineus levator ani (ATLA) both extend from the posterior surface of the pubic bone and end at the ischial spine.

Muscular Support

The levator ani (LA) muscle constitutes the primary muscular support to the pelvic organs. The LA muscle consists of three components – the pubococcygeus, puborectalis, and iliococcygeus, nomenclatures based on the origin and insertion of the muscle components (Fig. 1.5).

The anterior division of levator ani, the pubococcygeus, sweeps downward from the inner surface of the pubic bone along the sides of the urethra, vagina, rectum, and perineal body. This is further subdivided into the pubovaginalis, puboperinealis, and puboanalis. The pubovaginalis portion attaches to the lateral wall of vagina, the puboperinealis attaches to the perineal body, and the puboanalis portion attaches to the anus at intersphincteric groove.

The puborectalis, most caudal part of levator ani, originates from the inner surface of pubic bone and forms a U-shaped sling behind the anorectal junction and contributes to the anorectal angle.

The iliococcygeus portion arises from the ATLA and ischial spine on both sides and joins with each other at the iliococcygeal raphe and coccyx. The iliococcygeal raphe between the anus and coccyx is referred to as the levator plate and provides support to the rectum, upper vagina, and uterus. The openings between the levator ani muscles through which the urethra, vagina, and rectum pass is known as the urogenital hiatus. The whole expansion of the levator ani along with the coccygeus muscle, perineal membrane, and perineal body is the pelvic diaphragm.

Fig. 1.5

Levator ani muscle – pubococcygeus, puborectalis, and Iliococcygeus. U urethral opening, V vaginal opening, R rectum

Applied Anatomy

The normal resting levators maintain a constant state of contraction and relaxation occurs only during the elimination process (micturition, defecation, and parturition). Contraction of the pubococcygeus elevates the urethra and the anterior vaginal wall helping in urinary continence. Pubococcygeus and puborectalis contraction also elevates the anus and keeps the urogenital hiatus closed. Contraction of the levator ani can be assessed on rectovaginal examination while instructing the patient to squeeze the muscles as if holding bowels. The U-shaped muscle is felt along the side and posterior vaginal wall.

Neuromuscular injury to the levators such as during childbirth can lead to widening of the urogenital hiatus and lead to vertical inclination of the levator plate leading to dysfunction or prolapse of the pelvic organs (Fig. 1.6a, b).

Fig. 1.6

Levator plate in horizontal orientation (a) and levator plate with vertical inclination (b) (From: Beco [2]; with permission)

Levator avulsion, a documented injury of childbirth, was first reported as early as 1907. Using ultrasound imaging Dietz identified that levator avulsion involves detachment of the puborectalis portion from pelvic sidewall and it occurs in about 36 % after vaginal delivery. Avulsion can be diagnosed digitally by palpating the inferior pubic ramus and feeling for insertion of the puborectalis portion. In the presence of levator avulsion, 2–3 cm lateral to the urethra, bony surface of the pubic ramus can be palpated devoid of the muscle.

Perineal Membrane

A thick fibromuscular sheet that stretches across the anterior urogenital triangle of pelvic outlet, caudal to levator ani, is the perineal membrane (formerly known as the urogenital diaphragm). It attaches laterally to the ischiopubic rami and has a free posterior margin with anchorage at the perineal body. The urethra and vagina pass through the hiatus in perineal membrane (Fig. 1.7). The perineal membrane hence fixes distal urethra, distal vagina, and the perineal body to bony pelvis at the ischiopubic rami. The superficial perineal space lies external to the perineal membrane and contains the superficial perineal muscles, ischiocavernosus, bulbospongiosus and superficial transverse perineal muscles. The deep perineal pouch lies between the perineal membrane and levator ani and contains the external urethral sphincter, compressor urethrae, urethrovaginalis, and the deep transverse perineal muscles (Fig. 1.8).

Fig. 1.7

Perineal membrane, direction of the fibers and its attachment (From DeLancey [6]; with permission)

Fig. 1.8

Muscles of the deep perineal pouch

Perineal Body

The perineal body situated between distal vagina and anus is a point of convergence for different structures. The superficial perineal muscles, bulbospongiosus and superficial transverse perineal muscles, external anal sphincter, perineal membrane, deep transverse perineal muscles, distal part of the rectovaginal fascia, pubococcygeus and puborectalis portion of the levator ani all insert into this mass of connective tissue (Fig. 1.9). The perineal body plays an important role in the support of distal vagina and maintaining normal rectal function. In reconstructive surgeries, it is therefore important to restore the perineal body anatomy by proper re-approximation.

Fig. 1.9

Perineal body with its muscular attachments

Applied Anatomy

Orientation of the superficial perineal muscles in relation to vaginal outlet is important in reconstruction of the perineum (perineorrhaphy) and in episiotomy repair. In an ideal reconstruction, the widened genital hiatus is narrowed, and perineal body length is maintained.

Connective Tissue Support: Pelvic Fascia and Ligaments

The pelvic fascia has two components: parietal and visceral fascia. The parietal fascia covers the muscles along lateral pelvic wall and on the superior surface of pelvic diaphragm. The fascia covering the obturator internus muscle, obturator fascia, has two thickened portions: arcus tendineus levator ani (ATLA) and arcus tendineus fascia pelvis (ATFP), extending from the ischial spines to posterior surface of pubic bone. Portions of levator ani originate from ATLA, while the ATFP provides the lateral point of endopelvic fascial attachment (see Fig. 1.4).

The existence of the visceral fascia, in certain areas of pelvis and its various nomenclatures, has been an area of controversy in pelvic anatomy. The bladder and vagina are not enclosed in their own fascial layer, and the vagina appears to be separated from bladder anteriorly, only by the adventitial layer of vagina. The existence of a separate fascial layer between anterior vaginal wall and bladder has been of dispute on histological studies, and the nomenclature of pubocervical/pubovaginal fascia is being questioned. On the other hand condensation of the visceral fascia between rectum and vagina, the rectovaginal fascia, is an identifiable separate layer. This extends from the perineal body proximally to about 2–3 cm above hymenal ring. Above this level there is no separate fascial layer, and the endopelvic fascia attaches posterior vaginal wall laterally to pelvic side wall.

The endopelvic fascia is not a true fascia on histology and correct terminology would be endopelvic connective tissue. The term endopelvic fascia, however, is commonly used. Condensations of these fascia termed as ligaments include the uterosacral, cardinal, pubovesical, and pubourethral ligaments. The endopelvic tissue is a continuous layer extending from the uterosacral ligaments proximally to the pelvic portion of levator ani muscle distally, up to the level of urethra (Fig. 1.10).

Fig. 1.10

Schematic representation of the endopelvic fascia extent. USL uterosacral ligament

The endopelvic fascia also extends laterally across the pelvis, with its medial attachments to the lateral wall of cervix and vagina and lateral attachments to pelvic sidewall along the ATFP. This attachment stretches the vagina transversely between bladder and rectum and divides pelvis into an anterior and posterior compartment. The bladder and urethra occupy the anterior compartment the rectum and anal canal, posterior compartment and the uterus and cervix, the middle or apical compartment.

The three integrated levels of pelvic support projected by DeLancey to explain pelvic organ prolapse are defined by the endopelvic connective tissue attachments.

Level I Support

The cervix and upper vagina are suspended by the endopelvic fascia (parametria, paracolpium) and condensations of the connective tissue, uterosacral and cardinal ligaments. Uterosacral ligaments pass posteriorly from cervix and upper vagina, form lateral boundaries of pouch of Douglas, and attach to the front surface of sacrum from sacrococcygeal joint up to the level of S3. The cardinal ligaments (transverse cervical) extends from the cervix and lateral vaginal fornix to the posterolateral pelvic wall. These attachments are referred to as the level I or suspensory support. Failure of level I support leads to uterine or vaginal vault prolapse (apical prolapse).

Level II Support

The fascial attachment in mid-vagina extends from lateral vaginal walls to the ATFP and medial surface of levator ani. It prevents descent of the anterior and posterior vaginal walls with increase in abdominal pressure. This is referred as level II support or attachment axis. The differentiation between a central cystocele and a paravaginal defect in anterior compartment prolapse is based on the type of endopelvic fascia deficiency at this level. In central cystocele (distension cystocele), there is weakening of the connective tissue in midline, resulting in loss of midline rugosity of the vaginal wall. Lateral cystocele or paravaginal defect results from lateral detachment of fascia from the ATFP, and central rugosity are preserved in these. Prior to surgical intervention, it would be helpful to identify the type of anterior wall prolapse, lateral detachment or central failure to plan the optimal surgical technique.

The endopelvic connective tissue also extends as pubourethral ligaments, from the urethra to posterior surface of pubic bone, providing urethral support and maintenance of bladder neck closure during Valsalva maneuvers. The bladder neck in addition, through its relation to the anterior vaginal wall is indirectly supported by the attachment axis. Hence failure of level II support results not only in anterior and posterior vaginal wall prolapse but also to stress urinary incontinence.

Level III Support

The lower one-third of vagina is fused with the surrounding structures; through the endopelvic fascia anteriorly to distal urethra, posteriorly to perineal body, and laterally to pubovaginalis muscle and perineal membrane. This is referred to as the level III support or fusion axis. Level III disruption anteriorly can result in stress urinary incontinence from urethral hypermobility and posterior disruption can result in distal rectocele or perineal descent.

Ligaments Used in Reconstructive Surgery

Sacrospinous Ligaments (SSL)

The sacrospinous ligament with its lateral attachment at ischial spines has a close relationship with pudendal neurovascular bundle and to sciatic nerve (Fig. 1.11). The anterior surface of the SSL is muscular and forms the coccygeus muscle and is referred to as the coccygeus–sacrospinous ligament complex (C-SSL). The average length of the SSL is 5.43 cm and the position of the pudendal complex is about 0.9–3 cm medial to ischial spine behind the SSL. Suture placement for SSL fixation ideally should be 1.5–2 cm medial to ischial spine. It should never be across the entire thickness of the ligament to prevent damage to underlying structures. The sciatic nerve lies 2.5 +/− 0.4 cm lateral to the ischial spine posterior to SSL. On cadaver dissections, either the third sacral nerve or the pudendal nerve is found to course on the superior border of C-SSL complex at its midpoint in a significant proportion. The diligence in trying not to enclose the whole width of the ligament at SSL fixation is important for this reason.

Fig. 1.11

Coccygeus–sacrospinous ligament complex (C-SSL) with the pudendal nerve posterior to the ligament. Uterosacral ligament (USL) and relation to the sacral plexus, ureter, and Sciatic nerve

Uterosacral Ligaments

The uterosacral ligaments (USL) are attached distally to the posterior aspect of cervix and upper vagina and laterally merge with the cardinal ligaments. Proximally it has a diffuse sacral attachment to the pelvic surface of sacrum, vertically from sacrococcygeal joint to S3 vertebra and transversely from sacral foramina medially to 5 cm lateral to sacroiliac joint. USL is 12–14 cm long and can be subdivided into three sections: distal (2–3 cm), intermediate (5 cm), and proximal (5–6 cm). The distal portion is commonly used to anchor the vaginal apex in McCall’s culdoplasty. The proximal portion is diffuse in attachment and generally thinner. The intermediate portion is thick and well defined and is at least 2.5 cm away from the ureter and hence suitable for suspension procedures.

Interaction between Muscular and Connective Tissue Supports

The dynamic interaction between the muscular and connective tissue supports is critical for pelvic organ support. The pelvic organs are suspended over the levator plate by fascial support. The resting tone of levator ani muscle reduces the tension on the connective tissues due to their lateral muscular site attachments. With increase in intra-abdominal pressure, apart from the resting tone of levator ani and the closure of urogenital hiatus, there is further reflex contraction of pelvic floor musculature moving the pubococcygeus and puborectalis towards pubic bone. This further narrows the urogenital hiatus and prevents pelvic organ descent. All these reduces the strain on fascial support at times of increased abdominal pressure. It therefore follows that when levator muscles function normally, pelvic organ support is maintained. The interaction between the muscular and connective tissue support has been explained using the analogy of a ship floating in water attached by ropes on either side to a dock. The ropes represent endopelvic fascia, water pelvic floor muscles, and the ship, pelvic organs. When the pelvic floor muscles are intact structurally and neurologically, the endopelvic fascia is under less tension (akin to the ropes when water level is maintained). When the pelvic floor muscle weakens, fascia becomes the primary support mechanism in this scenario and overtime can weaken or break leading to prolapse or other pelvic dysfunction, like the ropes put under tension when water level is reduced.

Spaces in the Pelvis

Retropubic Space

The retropubic space also known as the space of Retzius is bounded anteriorly by symphysis pubis with the transversalis fascia inserting on the posterior surface of pubic symphysis. The urethra, urethrovesical junction, and anterior surface of bladder form the floor of retropubic space. The endopelvic connective tissue, extending from the lateral vaginal wall to pelvic side wall, partly contributes to the floor laterally (Fig. 1.12).

Fig. 1.12

Retropubic space – base of the space, boundaries and the vessels in area shown, as viewed from above (Reproduced with permission from Baggish [1])

The space assumes importance in pelvic surgery due to some important structures, nerves and vessels being related to it. The pectineal or Cooper’s ligament lies on the superior dorsal surface of pubic ramus, and a flat triangular extension of Cooper’s ligament, the lacunar ligament, widens as it travels medially and joins the inguinal ligament at pubic tubercle. The obturator canal lies approximately 1–2 cm below the upper margin of Coopers’ ligament.

Lateral to bladder and bladder neck, within the endopelvic connective tissue, lies the deep venous plexus (venous plexus of Santorini). The dorsal vein of clitoris drains into this venous plexus. Accessory obturator vessels from inferior epigastric or external iliac have also been noted in this space crossing the Cooper’s ligament in about 20–30 % of population. The venous plexus and the vessels coursing this area can be a source of bleeding during retropubic bladder neck suspension procedures, paravaginal defect repairs, pelvic lymph node dissections and with passage of needles and trocars through this space in midurethral sling procedures and mesh placements. Instruments traversing this area should ideally follow the medial portion of the space away from the urethra close to the bony structure. While medial deviation can lead to urethral injury, lateral deviation can lead to obturator or accessory obturator vessel injury.

Fig. 1.13

Presacral space – boundaries and relations shown (Reproduced with permission from Baggish [1])

Presacral Space

Presacral space extends from the aortic bifurcation above to pelvic floor below, with internal iliac vessels and ureters forming the lateral boundary (Fig. 1.13). The space lies between rectum anteriorly and the sacrum and coccyx posteriorly. There are several neural and vascular plexuses within this space. The median (middle) sacral artery arising from the abdominal aorta, descends in midline in front of the sacrum and coccyx in this space. The middle sacral artery anastomoses to the lateral sacral arteries, and sends offsets into the anterior sacral foramina. An extensive sacral venous plexus also occupies this space with anastomosis of medial and lateral sacral veins with contributions from lumbar veins. The neural plexus includes the superior hypogastric plexus with contributions from the inferior hypogastric plexus. The sacral artery and the venous plexus lie superficial to the anterior longitudinal ligament of sacrum, while the endopelvic fascia envelops the neural plexus in this area.

Awareness of this relationship is important in abdominal sacrocolpopexy (ASCP) procedure. The mesh in ASCP is secured to the anterior longitudinal ligament over S1 or S2 vertebrae. Identification of median sacral vessels intra-operatively is important to avoid vascular injury, since control of bleeding in this area can be challenging. Entry into the presacral space for ASCP and presacral neurectomies also requires knowledge of the proximity of iliac vessels, ureters and sigmoid colon in this region.

Anatomy of Lower Urinary Tract

In maintaining urinary continence, the structural anatomy of bladder and urethra play a role along with the neuronal control. The bladder epithelium is surrounded by smooth muscle layer, the detrusor muscle. The detrusor muscle has an