Anatomy: Perineum - UCLan 2024 PDF

XY2141. Anatomy. Perineum / ischioanal region Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected] Learning outcomes ANAT.31 - Perineum / ischioanal ANAT.31.01 - Discuss the location, arterial supply, and the venous and lymphatic drainage of the rectum a...

XY2141. Anatomy. Perineum / ischioanal region Dr Viktoriia Yerokhina, Lecturer in Medical Sciences [email protected] Learning outcomes ANAT.31 - Perineum / ischioanal ANAT.31.01 - Discuss the location, arterial supply, and the venous and lymphatic drainage of the rectum and anal canal. ANAT.31.02 - Compare and contrast the embryologic origin, lymphatic drainage and sensory innervation of the anal canal above and blow the pectinate line. ANAT.31.03 - Compare the internal and external submucosal venous plexus of the anal canal. ANAT.31.04 - Compare the location and symptoms of internal versus external hemorrhoids. ANAT.31.05 - Compare the location and innervation of the internal and external anal sphincters. ANAT.31.06 - Describe the basic process of defecation. ANAT.31.07 - Identify, in radiological images, major anatomical structures of the male and female pelvis. ANAT.31.08 - Compare and contrast the visceral pathways for structures above the peritoneal floor of the pelvis versus structures below the peritoneal floor. ANAT.31.09 - Compare and contrast the areas into which urine can be extravasated following an intrapelvic versus an extrapelvic rupture of the urethra. ANAT.31.10 - List the boundaries of the superficial perineal pouch. Explain why extravasated urine will not pass into the thighs or the ischioanal fossa. 2  Rectum A pelvic part of the digestive tract continuous proximally with the sigmoid colon and distally with the anal canal. Location: posterior part of the lesser pelvis in front of the lower three pieces of the sacrum and the coccyx; behind the urinary bladder in the male and uterus in the female.  Flexures/curvatures of rectum Rectum presents flexures/curvatures in both anteroposterior (sagittal) and lateral plane: In the sagittal plane: sacral and anorectal/perineal In the lateral plane: upper lateral, middle lateral, lower lateral. In Latin, the word “rectum” means straight; but the rectum is straight in quadrupeds and not in men. Interior of the rectum - folds 1.1 Transverse folds of rectum (plicae transversae recti) – three folds corresponding to the three flexures of the rectum Houston’s folds – superior and inferior transverse folds, located on the left side of the rectum Middle transverse fold of Kohlrausch – located on the right side of the rectum 5  Peritoneal relations of the rectum Upper 1/3 is covered with the peritoneum on the front and sides. Middle 1/3 is covered with the peritoneum only on the front. Lower 1/3 (ampulla) is not covered by the peritoneum at all. 6  Syntopy of rectum Dorsally, in both sexes: SIII–V, coccyx Laterally, in both sexes: pararectal fossae, levator ani Ventrally, in male: oral part: urinary bladder, seminal glands, rectovesical pouch of Proust aboral part: urinary bladder, seminal glands, ductus deferens, prostate Ventrally, in female: oral part: uterus, vagina, rectouterine pouch of Douglas aboral part: vagina, perineal muscles. Parts of the rectum 1. Ampulla 2. Anal canal 3. Anus 1. Rectal ampulla (ampulla recti) – dilated and longer part forming the sacral flexure – its mucosa features simple columnar epithelium as so is known as the colorectal zone 1.1 Anorectal junction – transition from the rectal ampulla to the anal canal at the level of pelvic diaphragm N.B. Ampulla lies below the level of rectovesical pouch in the male and rectouterine pouch in the female. Parts of the rectum 2. Anal canal - begins at the anorectal junction, passes downward and backward, and opens at the anal orifice, which is situated in the natal cleft (cleft between the buttocks) about 4 cm below and in front of the tip of coccyx. Anal canal is divided into upper and lower parts by the pectinate/dentate line. Pectinate line represents the embryological site of attachment of the anal membrane. Upper part - from the anorectal junction to the pectinate line; Lower part - from the pectinate line to the anal verge. 9  Features in the upper part of anal canal Anal transitional zone – area where the epithelium transitions from simple columnar to stratified columnar and finally to stratified squamous Anal columns (columns of Morgagni): 6-10 permanent longitudinal mucous folds, that contain radicles of the superior rectal vein. Anal valves (valves of Morgagni): crescentic folds of the mucousa which connect the lower ends of adjacent anal columns. Anal sinuses: vertical recesses between the anal columns and above the anal valves. 10 Features in the lower part of anal canal Further divided into two regions: a. Upper region (pecten): 15 mm long and extends from the pectinate line to Hilton’s/white line. Lined by non-keratinised stratified squamous epithelium. Mucosa in this region appears bluish due to underlying dense venous plexus. b. Lower region of lower anal canal: 8 mm long, lined by pigmented skin (keratinised stratified squamous epithelium) containing sweat and sebaceous gland. 3. Anus – hole covered by the skin with skin adnexa. 11 Muscles of the rectum 10. Internal anal sphincter – smooth muscle located in the oral part of the anal canal 11. External anal sphincter – skeletal muscle, attached externally to the internal anal sphincter and from below to the levator ani 12. Puborectalis – skeletal muscle, the most medial part of the levator ani, forms a sling around the rectum at the level of the anorectal flexure.  Muscles of the pelvic floor/pelvic diaphragm Organised into the shape of a funnel. They attach to the walls of the lesser pelvis and contain passages for the rectum, vagina and urethra. They contribute to the creation of intra-abdominal pressure and are part of the deep stabilising system. 1. Levator ani (m. levator ani) 2. Ischiococcygeus / coccygeus (m. ischococcygeus / coccygeus) 3. External anal sphincter (m. sphincter ani externus) 13  Levator ani (musculus levator ani) 1. Iliococcygeus (m. iliococcygeus) - tendinous arch of the levator ani 2. Pubococcygeus (m. pubococcygeus) - muscular bands between the coccyx and pubis 3. Puborectal (m. puborectalis) - muscular bands below the pubococcygeus. 14 Levator ani (musculus levator ani) Functions: compresses the organs of the pelvic outlet elevates the pelvic floor and anus contributes to the support of the uterus contributes to anorectal and urine continence (accessory sphincter of the anus) contributes to intra-abdominal pressure belongs to the deep stabilising system (together with the deep back muscles, diaphragm and muscles of the abdomen maintains the stability of the vertebral column) Innervation: pudendal nerve. 15  M. ischiococcygeus/coccygeus A thin muscle that merges with the sacrospinous ligament Function: pulls the coccyx ventrally to its former position (during defecation or delivery). 16  External anal sphincter (m. sphincter ani externus) Parts: 1. Subcutaneous part 2. Superficial part 3. Deep part Function: compresses the anal canal → maintains anorectal continence Innervation: pudendal nerve 17  Mechanism of defecation Accumulation of stool → Expansion of the rectal ampulla → Reflex relaxation of the internal anal sphincter → Voluntary relaxation of the external anal sphincter and puborectalis → Contractions of the muscular layer of the rectum → defecation. 18  Arterial supply 1. Superior rectal artery (chief artery of the rectum), a continuation of inferior mesenteric artery 2. Middle rectal arteries (2 in number) - from internal iliac artery 3. Inferior rectal arteries (2 in number) - from internal pudendal artery (from internal iliac) 4. Median sacral artery, a branch of the abdominal aorta. 19  Venous supply of the rectum 1. Superior rectal vein 2. Middle rectal veins (2 in number) 3. Inferior rectal veins (2 in number) Rectal veins arise from internal and external venous plexuses. Internal (haemorrhoidal) venous plexus is present in the submucousa and surrounds the anal canal above Hilton’s line. External venous plexus is present between the perianal skin and the subcutaneous part of the external anal sphincter, surrounds the anus. Rectal veins – arranged in a plexus called annulus hemorrhoidalis, which encircles lower part of the rectum and the anal canal. 21  Anastomoses of the rectum Superior rectal vein → to the inferior mesenteric vein → to the portal vein Middle rectal and inferior rectal veins → to the internal iliac vein → IVC Anastomoses between the portal and systemic veins are located in the wall of anal canal, making this a site of portocaval anastomosis. Anastomoses between the portal and systemic system are only clinically important when there is a blockage in the portal system, e.g. portal vein thrombosis, cirrhosis or hepatic vein stenosis. 22  Clinical correlation Common pathology above pectinate line: internal hemorrhoids, adenocarcinoma. Internal hemorrhoids (or true piles) - saccular dilatations of the tributaries of the superior rectal (hemorrhoidal) vein above the pectinate line in portal obstruction. Risk factors: older age and chronic constipation. Receive visceral innervation → not painful, but bleed profusely (!!!) on straining during defecation (passing stool).  Clinical correlation Below pectinate line: external hemorrhoids, anal fissures, squamous cell carcinoma. External hemorrhoids (or false piles) – dilatations of the tributaries of inferior rectal vein below the pectinate line. Receive somatic innervation (inferior rectal branch of pudendal nerve) → painful if thrombosed; ! do not bleed on straining during defecation. A 57-year-old patient complains of painless rectal bleeding during bowel movements. They report seeing bright red blood on the toilet paper. On examination, no external masses or discomfort are noted. What condition is most likely causing these symptoms? A. Anal fissure B. External hemorrhoids C. Internal hemorrhoids D. Colorectal polyps E. Inflammatory bowel disease 25 A 35-year-old patient presents with discomfort and pain during bowel movements, along with swelling and a lump near the anal opening below the pectinate line. What condition is most likely causing these symptoms? A. Internal hemorrhoids B. Extrenal hemorrhoids C. Adenocarcinoma D. Hirschsprung disease 26  Lymphatic drainage Lymphatics from the upper half accompany the superior rectal vessels and drain into the inferior mesenteric nodes. A few of these vessels are intercepted by the pararectal lymph nodes. Lymphatics from the lower half accompany the middle rectal vessels and drain into the internal iliac nodes and sacral lymph nodes. Lymphatics of the rectum are mostly arranged longitudinally in contrast to the lymphatics of most of the small and large intestines, where they are arranged transversely around the gut. When the carcinoma of the rectum spreads along lymphatics it does not cause rectal obstruction unlike the rest of the gut. 27 Clinical correlation Prolapse of rectum - protrusion of the rectum through the anus. 1. Incomplete prolapse (mucous prolapse): protrusion of rectal mucosa through the anus and occurs due to excessive straining during defecation. Pathogenesis: imperfect support of the rectal mucosa by the submucosa. 2. Complete prolapse (procidentia): whole thickness of the rectal wall protrudes through the anus. Causative factors: laxity of the pelvic diaphragm, excessively deep rectovesical or rectouterine pouch and inadequate fixation of the rectum in its presacral bed. 28 Summary 29  Perineum Lowest region of the trunk below the pelvic diaphragm, between the upper parts of the thighs and the lower parts of the buttocks. Contains external genitals and perineal muscles and is composed of urogenital triangle and anal triangle. Perineum is traversed by: urethra and anal canal in male, urethra, vagina, and anal canal in female. Surface features of the perineum: in male: penis, scrotum, and anal orifice, in female: vulva (female external genitalia) and anal orifice. 30  Boundaries Classified into: superficial and deep boundaries. Superficial Boundaries In lithotomy position, the perineum is diamond shaped and is bounded by: Anteriorly: scrotum in male and mons pubis in female. Posteriorly: buttocks. On each side: upper medial aspect of the thigh. 31 Deep boundaries Correspond to the boundaries of the pelvic outlet as follows: Anteriorly: Inferior margin of the pubic symphysis (actually arcuate pubic ligament) Posteriorly: Tip of the coccyx On each side: Anterolaterally: conjoint ischiopubic ramus Laterally: ischial tuberosity Posterolaterally: sacrotuberous ligament. 32 Urogenital triangle (trigonum urogenitale) Situated ventrally Borders: Ventrally: pubic symphysis Dorsally: a line connecting the left and right ischial tuberosities Laterally: ischiopubic ramus Floor (cranially): perineal membrane – contains the pelvic floor and perineal muscles. 33 Content of urogenital triangle Man: 1. Paired crus of penis and paired ischiocavernosus 2. Unpaired bulb of penis and unpaired bulbospongiosus 3. Paired bulbo-urethral glands of Cowper Woman: 1. Paired crus of clitoris and paired ischiocavernosus 2. Paired bulb of vestibule and paired bulbospongiosus 3. Paired greater vestibular glands of Bartholin and lesser vestibular glands 34  Perineal membrane A strong triangular membrane (fascial sheath) that stretches across the urogenital triangle between the ischiopubic rami at the sides. Perineal membrane has pouches on its superior and inferior surfaces. Perineal membrane forms the inferior boundary of deep perineal pouch and the superior boundary of superficial perineal pouch. 35  Perineal membrane In front, it is thickened to form the transverse perineal ligament and is continuous with the superior fascia of the urogenital diaphragm. Behind, it is fixed to the perineal body in the midline and splits into two layers. upper layer is continuous with the superior fascia of urogenital diaphragm, inferior layer is continuous as Colles’ fascia. 36 Perineal pouches Deep perineal pouch – a potential space between the deep fascia of the pelvic floor (superiorly) and the perineal membrane (inferiorly). Superficial perineal pouch – a potential space between the perineal membrane (superiorly) and the superficial perineal fascia (inferiorly). 37  Urogenital floor in male 1. Perineal membrane (membrana perinei) – a fibrous sheet covering the inferior aspect of the deep transverse perineal muscle 2. Deep transverse perineal muscle (m. transversus perinei profundus) – deep muscular part of the urogenital floor 3. Superficial transverse perineal muscle (m. transversus perinei superficialis) – forms the posterior border of the urogenital floor Muscles located superficial to the perineal membrane 4. Ischiocavernosus (m. ischiocavernosus) – compresses the crus of the penis, contributing to erection 5. Bulbospongiosus (m. bulbospongiosus) – evacuates the urethra during micturition and ejaculation Muscles located deep to the perineal membrane 6. External urethral sphincter (m. sphincter urethrae externus) 38 Urogenital floor in female 1. Perineal membrane – a fibrous sheet containing disperse muscle fibers 2. Superficial transverse perineal muscle (m. transversus perinei superficialis) – adjacent to the posterior edge of urogenital floor, weak or often absent Muscles located superficial to the perineal membrane 3. Ischiocavernosus – compresses the crus of the clitoris 4. Bulbospongiosus – compresses the vestibule, evacuating the vestibular glands Muscles located deep to the perineal membrane 5. External urethral sphincter 6. Compressor urethrae (m. compressor urethrae) – compresses and extends the urethra 7. Sphincter urethrovaginalis (m. sphincter urethrovaginalis) – compresses and extends the urethra 39  Perineal body - corpus perineale A pyramidal fibromuscular structure located in the midline of the perineum between the urogenital and anal triangles. It is the central insertion of the perineal and pelvic floor muscles. 40 Clinical correlation - episiotomy A surgical incision of the perineum during labour to prevent uncontrolled injury of the vagina, perineum and the baby. Midline episiotomy crosses the perineal body Medio-lateral episiotomy (30°from the midline) cuts through the bulbospongiosus and the superficial transverse perineal muscle. Left medio-lateral episiotomy is easily sutured, heals faster and therefore is performed more often. 41  Pelvic floor physical therapy Kegel exercises involve the contraction of the entire levator ani. These exercises especially strengthen the pubococcygeus muscles, which can treat stress incontinence, urge incontinence, and pelvic organ prolapse and assists in ejaculation. Exercises that target the pelvic floor to strengthen the muscles that control urinary flow and bowel movements To increase efficacy, exercises may be supplemented with: Weighted vaginal cones Biofeedback 42 Anal triangle – trigonum anale Situated dorsally; Borders: Ventrally: line connecting the left and right ischial tuberosities Dorsally: coccyx Laterally: sacrotuberous ligament and gluteus maximus. perineal muscles are missing here, pelvic outlet is closed by the pelvic floor muscles 43 Ischioanal fossa – fossa ischioanalis A paired space filled by adipose tissue surrounding the anus. Two fossae communicate with each other dorsally behind the anus. Function: form a space that allows the pelvic floor to span out during defecation and parturition. 44 Boundaries of ischioanal fossa Medio-cranially: 1. External anal sphincter 2. Inferior fascia of the pelvic diaphragm Laterally: 3. Ischial tuberosity 4. Obturator fascia Dorsally: 5. Inferior margin of the gluteus maximus 6. Sacrotuberous ligament Caudally: 7. Passes into the anal triangle 45 Content of ischioanal fossa 8. Pudendal canal of Alcock (canalis pudendalis) with internal pudendal artery and veins and pudendal nerve 9. Fat body of ischioanal fossa 46 Coronal section through the male pelvis and perineum, bladder and prostatic urethra 47 Pelvic fascia (female) 48 Sacral plexus Arises from the spinal nerves of S1 to S4 and recieves contributing branches from L4 and L5 via the lumbosacral trunk (truncus lumbosacralis). It is located on the pelvic surface of the sacral bone. Along with the lumbar plexus it provides somatomotor and somatosensory innervation for the lower limb. Nerves of the sacral plexus: 1. Superior gluteal nerve (n. gluteus superior) 2. Inferior gluteal nerve (n. gluteus inferior) 3. Posterior cutaneous nerve of thigh (n. cutaneus femoris posterior) 4. Pudendal nerve (n. pudendus) 5. Sciatic nerve (n. ischiadicus). Please, find the Sacral plexus in the lecture ‘Pelvis’ 49 Pudendal nerve – nervus pudendus – S2-S4 A major somatic nerve of the sacral plexus. Nerve roots – S2-S4 Sensory – innervates the external genitalia of both sexes and the skin around the anus, anal canal and perineum Motor – innervates various pelvic muscles, the external urethral sphincter and the external anal sphincter. 50 Branches of pudendal nerve and structures innervated Muscular branches – innervate the levator ani and ischiococcygeus Inferior rectal branches – innervate the external anal sphincter and provide somatosensory innervation to the skin around the intergluteal crest Perineal nerves and muscular branches – motor branches for the transversus perinei superficialis, transversus perinei profundus, bulbospongiosus and ischiocavernosus Posterior scrotal nerves – provide somatosensory innervation to the skin on the dorsal part of scrotum Posterior labial nerves – provide somatosensory innervation to the dorsal part of the labia Dorsal nerve of penis – provides somatosensory innervation to the penis and urethral mucosa Dorsal nerve of clitoris – somatosensory innervation of the clitoris. 51 Pudendal nerve block To relieve the pain associated with childbirth, certain types of chronic pelvic pain and in some rectal or urological procedures. Although the use of this procedure is less common since the widespread adoption of epidural anesthesia, it provides an excellent option for women who have a contraindication to neuraxial anesthesia (e.g., spinal anatomy, low platelets, too close to delivery). Pudendal nerve is infiltrated with a local anesthetic where it crosses the ischial spine. When the pudendal block is carried out bilaterally, there is a loss of anal reflex (useful test to know that a successful block is achieved), relaxation of the pelvic floor muscles, and loss of sensation to the vulva and lower one-third of the vagina. 52 REFERENCES MCQ for self-control 54