Functional Anatomy of Female Perineum

Abstract

Female perineum is the tissue complex between the peritoneum and the skin that closes the pelvis inferiorly and its functionality depends on the interplay between organs, tissues, septae and spaces in it. It is a diamond-shaped region below the pelvic floor and extends between the pelvic diaphragm and the perineal skin. It is a surprisingly dynamic field with new insights, discoveries, and controversies and carries differences in viewpoint among anatomists and surgeons. This book chapter will provide an overview regarding perineal anatomy in the female and will focus on embryology, anatomy of the perineal region with modern proponents. It includes detailed anatomy of Urogenital and Anal triangles, their muscles with blood supply and innervation, anatomy and functions of the perineum, its role in Pelvic Organ Prolapse and clinical significance in urinary and fecal incontinence and contribution towards common obstetric and gynecological pathologies.

1. Introduction

The perineum is situated below the pelvic diaphragm and is a diamond-shaped space. It is divided by an imaginary line between the anterior border of the ischial tuberosity into two triangular divisions, anteriorly the urogenital triangle and anal triangle posteriorly [1]. The urinogenital triangle is further divided by a fascial layer called the perineal membrane, into a deep perineal pouch, present above the perineal membrane and superficial perineal space present beneath it. Contents of the superficial perineal space are erectile tissues, skeletal muscles, and terminal branches of the internal pudendal vessels and nerves. Knowledge of the anatomy of the perineum is necessary to provide the best surgical outcomes in cases related to malignancies, trauma and congenital abnormalitiess.

2. Boundaries of the perineal region

The surface projection of the perineum is best visualized in the lithotomy position, with the individual lying in a supine position and the hip joints in partial flexion and abduction. Anteriorly, it is bounded by the arcuate ligament and lower border of the pubic symphysis, posteriorly by the tip of coccyx and ischiopubic ramus, anterolaterally by ischial tuberosities and the Sacro tuberous ligaments posterolaterally [2]. An imaginary inter-ischial line between the anterior ends of the ischial tuberosity divides the perineum into an anterior urogenital triangle and a posterior anal triangle (Figure 1).

Figure 1.

Boundaries of female perineum and division into urogenital and anal triangles.

The perineum is divided into superficial and deep compartments. Which are separated from each other Perineal membrane which is a fibrous connective tissue layer. The perineal membrane spans over the anterior half of the pelvic outlet. It was initially called the urogenital diaphragm; this modification of its name verifies that it is not a two-layered structure with muscle in between, as previously thought. The vagina and urethra are supported by the perineal membrane as they pass through it. Cephalad to the perineal membrane lies the striated urogenital sphincter muscle, which allows compression of the mid- and distal urethra [3, 4].

3. Embryology

Embryologically, the muscular pelvic part, is formed by two distinct muscle groups: the pubocaudal muscle and the muscle of Gegenbauer close to the cloaca.

The Pubocaudal muscle group gives rise to the levator ani and ischio-coccygeal muscle, pubourethral-bladder-uterus-rectosacral ligament and Gegenbauer group, after the descent of the genito-urinary septum forms the urethral and anal sphincter muscles and the superficial and deep transverse muscles, bulbocavernosus, and ischiocavernosus [5]. In fetus, these structures are present as a unit, synergistic in their functions.

The three divisions of the primitive gut are foregut, midgut, and hindgut and are derived from endoderm. The allantois and the hindgut enter the cloaca which is a common cavity and is in contact with the ectodermal surface. An ectodermal depression sinks in towards the gut until only the thin cloacal membrane remains between the gut and the outside. This is called the proctodaeum [6]. Partitioning of the cloacal membrane takes place during the fifth to seventh week of development when the mesodermal urorectal septum descends between the hindgut and the allantois to fuse with the cloacal membrane [7]. The area of fusion becomes the perineal body and separates the dorsal anal membrane from the larger ventral urogenital membrane. By the eighth week, the anal membrane breaks down, establishing the anal canal. The urorectal septum also divides the cloacal musculature into anterior and posterior components and thus explains why the nerve supply of the whole musculature is supplied by one nerve, the pudendal nerve [5].

4. Urogenital triangle

The urogenital triangle corresponds to the anterior region of the perineum. The perineal membrane divides the urogenital triangle into the deep perineal space (located above the membrane) and the superficial perineal space (located below the membrane). The perineal membrane is continuous with the superior fascia of the urogenital diaphragm [8]. At its apical end, the perineal membrane thickens to form the transverse perineal ligament [9]. The perineal membrane is anchored to the inferior surface of the ischio-pubic ramus on each side and extends posteriorly to attach to the perineal body posteriorly.

Through dissection and MRI, the perineal membrane is found to be neither a simple membrane nor a three laminar fascia-muscle-fascia unit. It is a complex multi-structure tissue integrated into a larger interconnected system, with varying histological composition according to the different structures. There is clear evidence of the presence of distinctive anterior and posterior portions that might play different roles [10].

Three fascial layers divide the superficial perineal space further into the subcutaneous perineal pouch and the superficial perineal pouch: the superficial fascia of the perineum, the deep perineal fascia, and the perineal membrane. The subcutaneous perineal pouch is limited by the superficial fascia of the perineum (Colle’s fascia) externally and the deep perineal fascia internally. Its thin layer of subcutaneous tissue, provides mobility to the skin over the external genitalia. The superficial perineal pouch is present between the perineal membrane and the deep perineal fascia. It is bounded by the inner surface of the ischiopubic ramus on either side and communicates anteriorly with the potential space between the Scarpa’s fascia and the fascia of the abdominal wall muscles [11].

The superficial perineal space contains the ischiocavernosus, bulbospongiosus, superficial transverse perineal muscles (superficial perineal muscles), the erectile tissue of the clitoris, the vestibular bulbs, and Bartholin glands. The deep perineal space lies inferior to the levator ani muscles just deep to the perineal membrane.

Within the deep perineal space lie the external urethral sphincter and the urethrovaginalis, compressor urethrae, and deep transverse perineal muscles. The urethrovaginalis and compressor urethrae muscles provide accessory sphincter function to the urethra. The urethrovaginalis muscles surround the distal urethra and vagina without passing between them, and therefore act as a sphincter to the vagina as well the distal urethra [3, 12].

The deep transverse perineal muscle, along with its superficial counterpart, serves to stabilize the position of the perineal body and inferior border of the perineal membrane. However, there is some dispute as to whether the deep transverse perineal muscle is present in females.

4.1 Muscles of perineum

Muscles of perineum include superficial transverse perineal, Bulbospongiosus and ischiocavernosus muscles (Figure 2).

Figure 2.

Muscles of perineum: lower layer of muscles, distal parts of urethra, vagina, rectum and perineal body. Patient supine. View into perineum.

4.1.1 Superficial transverse perineal muscle

The superficial transverse muscle, which arises from the inner and forepart of the ischial tuberosity and is inserted into the central tendinous part of the perineal body. It attaches to the central tendon of the perineal body along with its counterpart from the opposite side, the EAS from behind, and the bulbospongiosus in the front [8].

4.1.2 Bulbospongiosus muscle

It originates from the inferior surface of the superior pubic rami and the crura of the clitoris. Bulbospongiosus fibers blend with the superficial transverse perineal muscles and the external anal sphincter and inserts on the perineal body [13].

4.1.3 Ischiocavernosus muscle

This muscle is elongated, broader at the middle and is situated on the side of the lateral boundary of the perineum. It arises from the inner surface of the ischial tuberosity, behind the crura clitoris, from the surface the adjacent portions of the ischial ramusand surface of the crus [14].

4.2 Urethra

The female urethra is approximately 4 cm in length and 6 mm in diameter. Its lumen perforates the perineal membrane, with its external orifice in the vestibule directly above the vaginal opening. The urethra is embedded in the adventitia of the anterior vagina throughout its length. The urethral epithelium has longitudinal folds and many small glands, which open into the urethra [15]. The epithelium is continuous externally with vulval epithelium and internally with that of the bladder which is stratified squamous and becomes transitional near the bladder. The lamina propria supports the epithelial lining which is a layer of loose fibroelastic connective tissue. It contains collagen fibril bundles and fibrocytes and abundant elastic fibers spread longitudinally and circularly around the urethra. A characteristic feature are numerous thin-walled veins. This rich vascular supply contributes to urethral resistance. The urethral smooth muscle is composed primarily of oblique and longitudinal muscle fibers, with a few circularly oriented outer fibers. The intrinsic urethral sphincter mechanism is constructed by This muscle and the detrusor muscle in the bladder base. This smooth muscle is considered to be under alpha-adrenergic and cholinergic control, although Gosling et al. [16] found an extensive cholinergic nerve supply with few noradrenergic nerves. The longitudinal muscles shorten and widen the urethral lumen during voiding phase and the circular smooth muscle (along with the striated urogenital sphincter muscle) contributes to urethral resistance to outflow at rest. The extrinsic urethral sphincter mechanism is formed by the striated urethral and periurethral muscles. Its inner portion lies within and adjacent to the urethral wall, and outer portion is composed of skeletal muscle fibers of the pelvic diaphragm. The inner portion is made up of the sphincter urethrae, which surrounds the proximal two thirds of the urethra, and the compressor urethrae and urethrovaginal sphincter (known together formerly as the deep transverse perineal muscle), which arch over the ventral surface of the distal one third of the urethra. These three muscles functioning as a single unit, constitute the striated urogenital sphincter [11] which exerts tone on the urethral lumen over prolonged time periods. These muscles with the levator ani also contribute to voluntary interruption of the urine stream and urethral closure with stress via reflex muscle contraction.

4.3 Urethral support

Vagina provides support to the bladder and urethra. Support of the urethra and bladder neck is thought to be provided by the interplay of the pubourethral ligaments, the perineal membrane, and muscles of the pelvic floor.

For decades, the pubourethral and pubovesical ligaments have ben under debate. Few studies describe the pubourethral ligament as being one structure divided into two distinct portions (i.e., superior-inferior) [17] while others mention that it was divided into three portions (i.e., superiorintermediate-inferior), and some found that it comprises of two different ligaments (i.e., pubourethral and pubovesical ligaments).

It is also documented that the pubovesical ligament is an extension of the detrusor muscle and play a role in micturition by assisting vesical neck opening. This contradicts the existence of a so-called “pubovesical ligament” and states that it should be called the pubovesical muscle because its composition is mainly of smooth muscle cells [18].

DeLancey [19, 20, 21] reports that rather than being suspended ventrally by ligamentous structures, the proximal urethra and bladder base are supported in a sling model by the anterior vaginal wall, which is attached bilaterally to the levator ani muscles at the arcus tendineus fasciae pelvis (Figure 3). These attachments extend caudally and blend with the superior fibers of the perineal membrane. The tissues fix the distal urethra beneath the pubic bone and described as pubourethral ligaments, are composed of the perineal membrane and the lower portion of the arcus tendineus fasciae pelvis. Anterior vaginal attachment at the arcus tendineus fasciae pelvis may contribute to urethral closure by providing a stable base onto which the bladder neck and proximal urethra are compressed with increases in intra-abdominal pressure. These are responsible for the posterior movement of the vesical neck seen at the start of micturition and for the elevation seen when a patient is instructed to hold her urinary stream. Defects in these attachments probably result in anterior vaginal prolapse (cystocele) and proximal urethral support defects (urethral hypermobility) conditions associated with stress urinary incontinence. These defects are also responsible for paravaginal fascial defects, due to vaginal detachment from its lateral connective tissue supports [23].

Figure 3.

Pubourethral ligament (PUL), arcus tendineus fascia pelvis (ATFP), cardinal (CL), and uterosacral (USL). The vesico-vaginal ligament (VVL) is the attachment between the bladder base and proximal vagina. With permission from Dr. Peter Petros [22].

Coordination of the involuntary detrusor and intrinsic urethral sphincteric muscles ensure proper urinary continence mechanism and may be backed by the voluntary levator ani muscle and external urethral sphincter muscle function. The levator plate resists posterior rotational descent of the vagina and overlying urethrovesical junction during levator contraction providing a dynamic backdrop [24]. Pelvic musculature may be damaged during childbirth; consequently, posterior rotational descent of the bladder neck necessary for normal voiding can also occur at times of increased intra-abdominal pressure.

Relationship between urinary incontinence symptomatology and the number of repeated vaginal deliveries is documented. The risk for urinary incontinence was found to be contributing: 3.3%, 1.0%, and 6.8% after one, two, and three deliveries, respectively. The difference was significant after three vaginal deliveries, as compared to the first two (odds ratio, 3.2; confidence interval, 1.1–9.1) [25].

4.4 Blood and nerve supply of the region

The Pudendal nerve provides motor and sensory innervation of the perineum. Its origin is from S2 to S4 and exits the pelvis through the greater sciatic foramen, hooks around the ischial spine, and then travels along the medial surface of the obturator internus through the ischiorectal fossa in Alcock’s canal. It emerges posterior and medial to the ischial tuberosity and divides into three branches: Clitoral, Perineal and inferior rectal nerve to supply the perineum [14]. The blood supply to the perineum is via the pudendal artery, which travels with the pudendal nerve to exit the pelvis. Pudendal artery also has three main branches with rich collateral anastomoses supplying the area (Figure 4).

Figure 4.

Innervation of perineum.

5. Anal triangle

The anal triangle comprises of the anal canal, anal sphincter, perineal body, and ischiorectal fossa.

5.1 Perineal body

The perineal body is a fibromuscular structure that gives attachment to numerous structures and is located between the rectum and urogenital triangle. Anteriorly it is attached to the vaginal muscularis submucosa and the posterior border of the perineal membrane anteriorly where as pubovaginalis and puborectalis hold it in place anteriorly to the pubic bone. Laterally it is attached to the ischiopubic rami by superficial transverse perineal muscles. The perineal body communicates posteriorly and superiorly with the internal anal sphincter’s longitudinal fibrous sheath, which begins to curve anteriorly towards the posterior wall of the vagina at the level of the anorectal junction [26].

Dissection and histological studies results have shown that the PB is the site of insertion of different pelvic floor muscles. In contrast to a previous description of a superior and inferior portion, Larson et al. with the help of MRI described three portions: an inferior portion, a midportion, and a superior portion. The inferior portion gives attachments to the bulbospongiosus muscle, the superficial transverse perineal muscle, and the external anal sphincter. The midportion comprises the insertions of the superior aspect of the transverse superficial muscles, the pubovisceralis muscle (e.g., puboperinealis and puboanalis) as well as the internal and external anal sphincter muscles. The superior portion consists of the internal anal sphincter as well as some portion of the pubovisceralis (e.g., pubovaginalis and puboanalis).

5.2 Rectovaginal facia (RVF)

The existence of the RVF has been a topic of debate for many years among anatomists and surgeons [27]. The main point of discussion is whether a distinct membranous fascial structure exists between the vagina and the rectum in women and whether the rectovaginal space is merely filled with a mix of adipose tissue, fragmented membranous connective tissue, and muscle fibers. The RVF has been found to be separate from the anterior rectal wall by a layer of adipose connective tissue that surrounds the rectum and allows the two organs to move independently. Evidence confirms that the RVF can be clearly visualized and measured with MRI [28] and the findings correlate with the dissection observations.

5.3 Anal canal

Surgically anal canal is approximately 4 cm long and the rectum terminates in the anal canal. It runs from anal verge to the anorectal ring referred as the proximal part of the levator–external anal sphincter (EAS) complex [29]. It lies between the ischiorectal fossae laterally, the anococcygeal ligament posteriorly, and the perineal body anteriorly. The anal canal can be divided into following three divisions:

1. The first section, 15 mm long, lined by a stratified cubic epithelium, extends from anorectal junction to the dentate line. The anal columns, which consist of 6–10 vertical folds, called the columns of Morgagni house a terminal radicle of the superior rectal artery and vein. Subepithelial tissues expand into three anal cushions. These cushions seal the anal canal and help maintain continence of flatus and liquid stools. The mucosal folds known as the anal valves, connect the lower ends of the columns, contain tiny depressions known as anal sinuses. Embryologically dentate line is the site of anal membrane which first appears at the confluence of the ectodermic (derived from proctoderm) and endodermic (derived from cloacae) and entodermic (derived from the cloacae) portions of the anal canal.

2. The transition zone, or pecten, is the second section and is 15 mm long. It is a lined by stratified, nonkeratinized squamous epithelium that lacks hair follicles, sweat and sebaceous glands, but is rich in somatic nerve endings. It corresponds to the intersphincteric anal groove and extends from the dentate line to the white line of Hilton.

3. The third portion, which is 10-mm long and continuous with the skin, is situated inferiorly to the Hilton white line.

The puborectalis muscle, the internal and external anal sphincters, and the sphincteric complex all surround the anal canal’s walls. As a result of tonic circumferential contraction of the sphincter, the skin is arranged in radiating folds around the anus and is called the anal margin [30].

5.4 Anal sphincter complex

The anal sphincter complex is made up of the internal anal sphincter (IAS) and external anal sphincter (EAS) separated by the conjoint longitudinal coat. Both are different in structure and function even though they function as a single entity. When the rectum inserts into the pelvic diaphragm, the inner circular muscle of the rectum continues to the IAS and terminates approximately 1 cm proximal to the distal edge of the EAS. The IAS is found to be approximately 2–3 mm in thickness and to become thicker near the anal verge. Innervation for IAS comes from the inferior pelvic plexus which constitutes both sympathetic and parasympathetic fibers, splanchnic nerves (S2–4) also innervate this muscle, having a parasympathetic portion only. Due to this nerve supply, there is a constant resting pressure which may reflect the tone of the IAS [31]. With solid stool in the rectum, the IAS begins to relax, and the external anal sphincter begins to contract; this is called the rectoanal inhibitory reflex.

The EAS is a striated muscle that forms a muscular cylinder around the anal canal including the entire length of IAS and Conjoined longitudinal Muscle (CLM). It is innervated by the inferior rectal branch of the pudendal nerve. The EAS is considered to have one or more subdivisions, although the precise composition is disputed [32]. It consists of subcutaneous, superficial, and deep components. From a surgical viewpoint, these distinctions are less relevant. The deep portion of the external sphincter does not have posterior attachments. Its fibers are intimately related to the puborectalis muscle and insert anteriorly into the perineal body. The anococcygeal ligament is a dense connective tissue structure that attaches the superficial portion of the EAS to the tip of the coccyx. The subcutaneous part is circular but may have attachments to the perineal body anteriorly and the anococcygeal ligament posteriorly. In an endorectal ultrasound, the EAS appears as a hyperechogenic structure. In contrast with other skeletal muscles, the EAS maintains an unconscious resting electrical tone through a reflex arc at the cauda equina level, and thus generates 25–30% of the resting anal sphincter tone. Reflexive or voluntary contraction of the EAS/puborectalis works together to prevent fecal leakage. An active contraction can only be sustained for 30–60 seconds [33]. With solid stool in the rectum, the IAS begins to relax, and the external anal sphincter begins to contract; this is called the rectoanal inhibitory reflex.

5.5 The longitudinal layer and the conjoint longitudinal coat

The longitudinal muscle of the rectum fuses with striated fibers of the levator ani and puborectalis muscles at the level of the anorectal ring to form the conjoined longitudinal muscle. The fibers descend between the internal and external anal sphincters and consist of a fibromuscular layer, Distally, this muscle lamina becomes fibroelastic and divides into about 10 fibroelastic septa irradiating and crossing the subcutaneous part of the external sphincter to insert into the perianal skin forms the corrugator cutis ani [34, 35].

5.6 Innervation of the anal sphincter complex

IAS is a continuation of the circular fibers of the rectum, it shares the same innervation: sympathetic (L5) and parasympathetic nerves (S2–S4). The conjoint longitudinal coat is innervated by autonomic fibers from the same origin. The EAS is innervated by the inferior rectal branch of the pudendal nerve [32].

5.7 Vascular supply

The anorectum receives its major blood supply from the superior (terminal branch of the inferior mesenteric artery) and inferior haemorrhoidal (branch of the pudendal artery) arteries, and to a lesser degree, from the middle haemorrhoidal artery (branch of the internal iliac), forming a wide intramural network of collaterals. The venous drainage of the upper anal canal mucosa, IAS and conjoint longitudinal coat passes via the terminal branches of the superior rectal vein into the inferior mesenteric vein. The lower anal canal and the EAS drain via the inferior rectal branch of the pudendal vein into the internal iliac vein [33].

5.8 Lymphatic drainage

The anorectum is rich in lymphatic plexuses. The dentate line represents the interface between the two different systems of lymphatic drainage. Above the dentate line (the upper anal canal), the IAS and the conjoint longitudinal coat drain into the inferior mesenteric and internal iliac nodes [36]. Lymphatic drainage below the dentate line, which consists of the lower anal canal epithelium and the EAS, proceeds to the external inguinal lymph node.

5.9 Ischioanal fossa

The ischioanal fossa is a space filled with fat lateral to the anal canal and just below the pelvic diaphragm. It has a shape of a triangular pyramid with the apex at the boundary of the anal canal and the obturator fascia, and the base directed towards the perineal surface and is bound anteriorly by the perineal membrane, superiorly by the fascia of the levator ani muscle and medially by the EAS complex at the level of the anal canal. The lateral border is formed by the obturator fascia and inferiorly by a thin transverse fascia, which separates it from the perianal space. The ischioanal fossa contains fat and neurovascular structures, including the pudendal nerve and the internal pudendal vessels, which enter through Alcocks’s canal [35].

6. Clinical considerations

6.1 Support to anorectum in pelvic organ prolapse (POP)

The sphincter vaginae (pubovaginalis) muscle passes through the perineal body and blends with the deep part of the external anal sphincter, anchoring the perineal body to the anal canal. In addition, the upper surface of the perineal body joins with the rectovaginal septum (Denonvilliers’ fascia), and into its very posterior and superior aspects, pass fibers from the longitudinal muscle layer of the muscularis externa of the anterior wall of the rectum.

The perineal body is also attached to the muscles in the superficial and deep perineal spaces. Various components of the external anal sphincter, superficial transverse perineal muscles, levator ani (pubococcygeus, pubovaginalis, and puborectalis), and the median part of the posterior border of the perineal membrane are also attached to the perineal body making it to anchor the anterior anorectal region to the pelvic ring [24, 37, 38, 39].

An increase in the size of the urogenital hiatus is directly related to progressively larger pelvic organ prolapses that correlate more to the anterior-posterior (A-P) diameter than to the transverse diameter. Woodman [24] observed that it was actually the levator ani and not the perineal body that closes the urogenital hiatus. DeLancey and Hurd’s (1998) data were consistent with this finding. The urogenital hiatus is sealed by the vaginal walls, endopelvic fascia, and urethra. As the urogenital hiatus increases in size, however, an open space develops in the pelvic floor and gravity tends to fill this space with a cystocele, rectocele, or the uterine cervix. Once the urogenital hiatus has opened up, the vaginal wall and cervix lie unsupported, and the endopelvic fascia is called upon to hold the pelvic organs in place. In predisposed individuals the constant load from abdominal pressure on this fascia can cause its failure with the development of significant prolapse. Ultimately, it is the perineal body that acts as the final mechanism for preventing prolapse beyond the urogenital hiatus. As the perineal membrane and tendinous arches of the pelvic fasciae tighten, the entire perineal body redirects abdominal pressure and dissipates gravity to prevent expansion of the urogenital hiatus.

6.2 Support to vagina

According to Woodman [24], the perineal body acts as Level III support to the immobile inferior one-third of the vagina. It serves to close the vagina and prevents its eversion.

He further described the perineal body s as the central connection between the two halves of the perineal membrane. As force is directed upon the vagina from above, the fibers of the perineal membrane, which are laterally and posteriorly attached to the ischiopubic rami and perineal body, respectively, become taut and resist downward displacement.

There is also structural interdependence between the support offered by the perineal body at Level III through its attachment to the perineal membrane and the suspension of the vagina by the perineal body at Level II (arcus tendinous fasciae pelvis and the levator ani in the middle one-third of the vagina) [4].

6.3 Obstetric injury to perineum

Perineal repair after childbirth affects millions of women across the globe. The prevalence of perineal trauma varies as it is dependent on obstetric practice including rates and types of episiotomies. Obstetric anal sphincter injuries (OASIS) occur in 1.7% (2.9% in primiparas) of women in centres where mediolateral episiotomies are practiced compared to 12–19% (19% in primipara) in centres practicing midline episiotomy [40].

It has been shown that up to half of OASIS are not recognized. Inadequate training of doctors and midwives in perineal and anal sphincter anatomy is believed to be a major contributing factor. However, despite recognition and primary repair of acute OASIS, 39–61% have symptoms of anal incontinence and 92% have persistent anal sphincter defects on ultrasound within 3 months of delivery [26]. The morbidity associated with perineal trauma depends on the extent of perineal damage, technique and materials used for suturing and the skill of the person performing the procedure.

6.4 Fecal continence

Because of its close relationship to the anal canal and anal sphincter muscles, the most important function of perineal body is to maintain fecal continence. The insertion and passage of internal and external sphincters into the perineal body is explained by Shafik [33]. Therefore damage to the perineal body causes direct (or indirect) extension into the anal sphincters and a loss of fecal continence is possible.

6.5 Urinary continence

The urinary continence mechanism is complex and involves the coordination of the involuntary detrusor and intrinsic urethral sphincteric muscles. The levator ani muscle and external urethral sphincter muscle which are under voluntary control function as backup mechanisms, The levator plate is also a dynamic backdrop for the normal continence mechanism as it resists posterior rotational descent of the vagina and overlying urethrovesical junction during levator contraction. As a result of childbirth and subsequent damage to pelvic musculature, posterior rotational descent of the bladder neck can also occur at times of increased intra-abdominal pressure. The urethrovaginal sphincter attaches to the perineal body and contributes to the external urethral sphincter. Neurologic and direct damage to the pelvic floor can occur during delivery, and subsequent loss of urethrovaginal sphincter function may be just enough to make a woman incontinent [12].

Benson summarized the neurogenic hypothesis of urinary incontinence. Partial denervation of Levator Ani can occur after childbirth through direct compression, stretch, and devascularization of the pudendal nerve resulting in levator ani atrophy and loss of urethral and bladder support which contributes to urinary incontinence [41]. Various studies described the factors associated with urinary incontinence and found out that spontaneous and deliberate trauma to the perineal body is associated with urinary incontinence and not episiotomy, but only perineal suturing continued to be associated with urinary incontinence [42, 43].

7. Conclusion

Female perineum plays an essential role in Pelvic organ prolapse, urinary and fecal incontinence and vaginal delivery. Therefore, knowledge of the regional anatomy and function is essential for management of disorders.

Conflict of interest

No conflict of interest.

Note of thanks

We would like to thank Dr. Peter Petros for his permission to use figures from his articles and book chapters [22].