Perenium I and II Richard J. Krieg, Jr., PhD OBJECTIVE: • To gain a fundamental knowledge of the male and female perineum with respect to their gross anatomical structure, function, and clinical correlates. READING REFERENCE: • Moore & Agur, Essential Clinical Anatomy ("ECA"), pp. 248­270. LEARNING RESOURCES: • Optional films, Tapes and CDs at the Computer Based Instruction Laboratory (CBIL). I. Perineum in General The perineum is a diamond­shaped area at the base of the trunk. Fig 1 The boundaries are (ECA, Fig. 3.24): 1. Anteriorly ­ the pubic arch and pubic symphysis 2. Laterally ­ the ischial tuberosities 3. Posteriorly ­ the sacrotuberous ligament and coccyx The perineum is bisected into an anteriorly placed urogenital triangle and a posteriorly placed anal triangle by a line which passes through the ischial tuberosities (ECA, Fig. 3.24). Fig 2 II. Anal Triangle The anal triangle includes the anal canal and the ischiorectal fossae which flank either side of the anal canal. The pelvic diaphragm separates the ischiorectal fossae from the pelvis above and the anal canal below ("Levator ani" ECA, Fig. B3.8, p. 257). The pelvic diaphragm also extends into the urogenital triangle, where it is located above the urogenital diaphragm (See Figure Below and Atlas, 12 th ed.: 3.21C, 11 th ed.: 3.14D). Fig 3 A. Ischiorectal fossa This is a fat­filled space on either side of the anal canal and rectum and serves the purpose of allowing these organs to expand and contract. 1. Borders of the fossa: a. Laterally ­ obturator internus The fascia covering the obturator internus is the obturator internus fascia, and it separates the muscle from the ischiorectal fossa (ECA, Fig. 3.27B, p. 255). b. Supero­medially ­ levator ani The "infraanal fascia" or "inferior fascia of the peIvic diaphragm" covers the inferior side of the levator ani muscle and separates it from the ischiorectal fossa (“Inferior fascia of levator ani”, ECA, Fig. 3.27, p. 255). c. Anteriorly ­ the "anterior recess of the ischiorectal fossa" extends superior to the urogenital diaphragm, between itand the inferior part of the pelvic diaphragm (See Figure Below). d. Posteriorly ­ sacrotuberous ligament and the overlying gluteus maximus muscle Fig 4 2. In the fascia of the obturator internus muscle, on the lateral boundary of the ischiorectal fossa, lies the pudendal canal. This is the region in which a pudendal block would be performed. 3. The inferior rectal nerves travel right across the ischiorectal fossa to reach the lower part of the rectum and the anal canal to innervate the external sphincter of the anal canal. Severance of these nerves in this region results in incontinence. Fig 5 B. Pelvic Diaphragm (see accompanying figure; Atlas, 12 th ed.: 3.9, 3.10, 11 th ed.: 3.4) The pelvic diaphragm is made up of two muscles: the levator ani and the coccygeus. 1. The levator ani arises in part from the pubis as the puboccygeus muscle. The puborectalis muscle is a bundle that passes around the rectum to form the puborectalis sling. This sling is important to the support of the rectum and anal canal, and assists the external anal sphincter muscle to control the passage of feces. In the male, part of the pubococcygeus also supports the prostate gland and can thus be termed the levator prostatae. In the female, the pubococcygeus contacts the vagina and can act as a vaginal sphincter. Part of the pubococcygeus is also thought to control the passage of urine, such that micturation requires the relaxation of this pubovesicalis muscle and the specific urethral sphincter (to be seen later in the deep perineal pouch). Fig 6 The other part of the levator ani is the iliococcygeus muscle which arises from the arcus tendineus and the spine of the ischium. The arcus tendineus is a thickening of the fascia of the obturator intemus which is located superior to the pudendal canal. 2. The coccygeus muscle (ischiococcygeus) is not part of the levator ani, but is part of the pelvic diaphragm. It extends from the ischial spine to the lower sacrum and coccyx. The muscle is covered externally by the sacrospinous ligament. 3. As the lower part of the large intestine passes through the pelvic diaphragm it abruptly changes course from an infero­anterior direction to a downward or even infero­posterior direction. This perineal flexure marks the transition from rectum to anal canal. C. Anal sphincters The external anal sphincter (Atlas, 12 th ed.: 3.51, 11 th ed.: 3.44) is classically considered to have three parts: subcutaneus, superficial, and deep. The deep part of the external anal sphincter is the most important sphincter of the three, and acts with the puborectalis muscle to maintain anal continence. The superficial part of the external anal sphincter attaches posteriorly to the coccyx and anteriorly to the perineal body to anchor the anus. Just posterior to the rectum, the ischiorectal fossae from either side are continuous with each other such that an infection of the fossae can assume a horseshoe shape. The area through which the fossae connect posteriorly is between the superficial and deep parts of the external anal sphincter. The external anal sphincter is supplied mainly by the inferior rectal nerve, but the anterior part of the muscle may be innervated by the perineal branch of the pudendal nerve. Fig 7 The internal anal sphincter is simply the circular muscular coat of the wall of the large intestine. D. Internal structure of the anal canal The anal columns are located at the upper end of the anal canal. The bases of the anal columns are connected by anal valves (See Figure Below). The line formed by the anal valves (and the bases of the anal columns) is called the pectinate or dentate line. This is an important landmark which will separate internal from external hemorrhoids. The pectinate line is located approximately 1­5 centimeters from the anal opening. Below the pectinate line is the "pecten”. At this "mucocutaneous line" a transition takes place involving epithelium, innervation, and venous and lymphatic drainage. Fig 8 E. Blood supply of the rectum and anal canal (Atlas, 12 th ed.: 3.17A, 11 th ed.: 3.10) 1. Superior rectal artery and vein from the inferior mesenteric artery and vein 2. Middle rectal artery and vein from the internal iliac artery and vein 3. Inferior rectal artery and vein from the internal pudendal artery and vein Since the middle rectal vein drains the muscular coat of the rectum, it is usually not involved in the development of hemorrhoids. The superior rectal vein drains the mucosa superior to the pecten and the inferior rectal vein drains the mucosa inferior to this area. Due to the lack of muscular tissue support for these very superficial veins, the superior and inferior rectal veins are commonly involved in hemorrhoids. Fig 9 In general, internal hemorrhoids are located superior to the pectinate line and involve the superior rectal vein, and external hemorrhoids are inferior to the pectinate line and involve the inferior rectal vein. Internal hemorrhoids are the most common due to the number of factors that make the superior rectal vein more prone to varicosities. Since the superior rectal vein drains into the inferior mesenteric vein and subsequently into the hepatic portal system, and since the inferior rectal vein drains into the internal pudendal vein, then the internal iliac vein and eventually into the inferior vena cava, the abundant anastomoses between these vessels in the mucosa of the anal canal act as one of the more significant sites of porta­ caval anastomoses. III. The Male Urogenital Region A. Fascia 1. Superficial fascia The membranous layer of the superficial fascia of the abdomen (Scarpa’s fascia) forms the superficial fascia of the perineum ­ Colles' fascia (See Figure Below). It also forms the dartos tunic of the scrotum (See Figure Below). It attaches to the fascia lata laterally, to the ischiopubic rami, and to the posterior edge of the perineal membrane to enclose the superficial perineal pouch. Fig 10 2. Deep fascia a. The perineal membrane is one of two membranes which enclose the deep perineal pouch. The two layers are also more simply termed the inferior and superior fascias of the urogenital diaphragm (perineal membrane & pelvic fascia, respectively ­ See Figure Below Fig 11 b. Deep fascia of the penis (ECA, figure 3.25A) ­ Buck's fascia This fascia is closely applied to the penis, deep to the superficial fascia. It covers the shaft and root of the penis. B. Superficial perineal pouch 1. As mentioned above, the superficial perineal pouch is formed by the superficial perineal fascia (Colles' fascia) as a continuation of Scarpa's fascia, and finally attaches at the posterior edge of the urogenital diaphragm. 2. The contents of the pouch in the male are: a. Bulb of the penis with bulbospongiosus muscle b. Crura of the penis with ischiocavernosus muscles c. Superficial transverse perinei muscles (ECA, Fig. 3.31A, Atlas, 12 th ed.: 3.51, 11 th ed.: 3.44) d. Perineal branch of the pudendal nerve e. Posterior scrotal and muscular branches of the perineal nerve (ECA, Fig. 3.31A, Atlas, 12 th ed.: 3.51, 11 th ed.: 3.44) f. Perineal and posterior scrotal arteries (Atlas, 12 th ed.: 3.51, 11 th ed.: 3.44) Fig 12 Fig 13 Fig 14 C. Deep perineal pouch 1. The deep perineal pouch is formed by the inferior and superior fascias of the urogenital diaphram. 2. The contents of the deep perineal pouch of the male include: a. Deep transverse perinei muscles b. Sphincter urethrae muscle c. Membranous urethra d. Dorsal nerve of the penis (ECA, Fig.