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Surgical anatomy anal canal
- 1. Surgical anatomy- anal canal by: Dr. Belal Mansoor Taiz university 18/3/2018
- 2. Overview Introductions Location , extent , Dimensions of anal canal Embryology The anorectal ring ,The puborectalis muscle Anal sphincters & The intersphincteric plane The epithelium and sub epithelial structures(internal). Blood supply ,Lymphatic drainge ,& Nerve supply Clinical aspects
- 3. The anal canal • The anal canal remains an area of medicine and surgery plagued by obscurity and limited provider knowledge. • Many conditions are in fact common and benign, but some lead to incapacitating interference with the patient’s daily life. SABISTON TEXTBOOK of SURGERY 20th EDITION
- 4. The anal canal • Therefore, attempts to improve our fund of knowledge of the anatomy and function of the anal canal and the basic physiology of the pelvic floor. » should facilitate accurate diagnosis and management of both common and rare conditions. SABISTON TEXTBOOK of SURGERY 20th EDITION
- 6. The anal canal The surgical anal canal The anatomic anal canal
- 7. The surgical anal canal • The surgical anal canal: –It begins at the anorectal junction – terminates at the anal verge.
- 8. The surgical anal canal • The muscular junction between the rectum and anal canal can be felt with the finger as a thickened ridge – the anorectal ‘bundle’or ‘ring’. Bailey & Love’s 26th EDITION
- 9. The surgical anal canal- Dimensions • The surgical anal canal measures 2 to 4 cm in length and is generally longer in men than in women. Schwartz’s Principles of Surgery Tenth Edition
- 10. The anatomic anal canal • The anatomic anal canal extends from the dentate or pectinate line to the anal verge.
- 13. Posteriorly: Anteriorly: In the male,: the perineal body,, the membranous part of the urethra, and the bulb of the penis
- 14. Anteriorly: In the female ,: the perineal body ,the lower part of the vagina
- 15. Laterally: The fat-filled ischiorectal fossae
- 16. The anal canal below the pectinate line develops from the proctodeum (ectoderm), while that above the pectinate line develops from the endoderm of the hindgut.
- 17. • The congenital anomaly in which the anal canal fails to communicate with the exterior is known as imperforate anus. Imperforate anus is a congenital anomaly in which the anal canal fails (completely or incompletely) to open to the exterior.
- 19. • The anal canal is completely extraperitoneal.
- 24. The Anorectal Ring • The anorectal ring marks the junction between the rectum and the anal canal . • It is formed by the joining of : the puborectalis muscle the deep external sphincter, conjoined longitudinal muscle the highest part of the internal sphincter
- 26. • The anorectal ring • The anorectal ring can be clearly felt digitally, as a thickened ridge , especially on its posterior and lateral aspects.
- 28. the puborectalis muscle • At rest, the puborectalis muscle creates a “sling” around the distal rectum, forming a relatively acute angle that distributes intra- abdominal forces onto the pelvic floor. • With defecation, this angle straightens, allowing downward force to be applied along the axis of the rectum and anal canal. • Nonrelaxation of puborectalis results in straining and incomplete evacuation.
- 29. Anal sphincters The internal sphincter external sphincter
- 30. The external sphincter • Voluntary sphincter • Composed of skeletal muscle. Surrounds entire length of anal canal • Consists of 3 parts – Subcuatneous Superficial & Deep • Nerve supply: – Inf. Rectal br. Of pudendal n. – Perineal br. of 4th sacral n.
- 31. The external sphincter • Consists of 3 parts deep superficial subcutaneous The parts blend with one other to form a continuous tube.
- 32. The external sphincter The deep external anal sphincter : ring, together wiht the puborectalis muscle. Superficial : elliptical ,and attached to coccyx Subcutanenous :ring
- 34. • Anorectal sphincter tone can be assessed during digital rectal examination (DRE) when the patient is asked to squeeze the examining finger. The external sphincter
- 35. The intersphincteric plane • Between the external sphincter muscle laterally and the longitudinal muscle medially exists a potential space, the intersphincteric plane. • The plane can be opened up surgically to provide access for operations on the sphincter muscles.
- 36. The longitudinal muscle The longitudinal muscle is a direct continuation of the smooth muscle of the outer muscle coat of the rectum.,
- 37. At the anorectal junction the outer longitudinal layer of rectal m. become fibro elastic and, together with some striated muscles fibres of puborectalis , forms he conjoint longitudinal coat which runs down between the two sphincters.
- 40. The internal sphincter • When exposed during life, it is pearly-white in colour and its circumferentially placed fibres can be seen clearly.
- 41. The anal sphincter mechanism : allows defecation . maintains continence.
- 42. The Defecation • Defecation has four components: 1. mass movement of feces into the rectal vault. 2. rectal–anal inhibitory reflex, by which distal rectal distention causes involuntary relaxation of the internal sphincter; 3. voluntary relaxation of the external sphincter mechanism and puborectalis muscle; 4. increased intra-abdominal pressure.
- 43. The Continence • Continence requires: normal capacitance, normal sensation at the anorectal transition zone, puborectalis function for solid stool, external sphincter function for fine control, internal sphincter function for resting pressure.
- 44. THE INCONTINENCE • INCONTINENCE: – is the inability to prevent elimination of rectal contents. • Etiologies include : – (1) mechanical defects, – sphincter damage from obstetric trauma, fistulotomy, and scleroderma affecting the external sphincter; – (2) neurogenic defects, – spinal cord injuries, pudendal nerve injury due to birth trauma or lifelong straining, and systemic neuropathies such as multiple sclerosis; and – (3) stool content-related causes, – such as diarrhea and radiation proctitis.
- 46. Interior of anal canal
- 48. Interior of anal canal
- 49. Interior of anal canal
- 50. The anal valves join together the lower ends of the anal columns
- 51. most important landmark both morphologically and surgically
- 53. The pectinate line • The pectinate line is not seen on inspection in clinical practice, but under anesthesia the anal canal descends down, and the pectinate line can be seen on slight retraction of the anal canal skin.
- 54. The anal sinuses are furrows in the anal canal, that separate the anal columns from one another. The anal sinuses end below in small valve-like folds, termed anal valves.
- 55. The glands themselves are located at varying depths in the anal canal wall
- 58. The pecten: is a smooth area of hairless stratified epithelium that lies between the anal valves superiorly and the inferior border of the internal anal sphincter inferiorly.
- 60. ANAL FISSURE: it is a split in the anoderm. (a longitudinal tear in the mucosa and skin of the lower third of the anal canal). 90%occur posteriorly (comparatively low blood flow)
- 61. If surgery is required, lateral internal sphincterotomy is 90% successful. ANAL FISSURE
- 62. Blood supply • The blood supply is based on embryology: • ■ Hindgut: Inferior mesenteric artery (IMA) • ■ Distal anus: Internal pudendal artery branches
- 63. arterial supply – above dentate line: • superior rectal artery (from inferior mesenteric artery); • small contributions from middle rectal artery (directly from internal iliac artery) and median sacral arteries – below dentate line: • inferior rectal artery (from internal pudendal artery).
- 68. venous drainage: • continuous with rectal venous plexus (i.e. rich anastomoses). – above dentate line: • superior rectal vein to inferior mesenteric vein (portal venous system) – below dentate line: • inferior and middle rectal veins to internal iliac veins • The anal canal is a site of portosystemic anastomosis.
- 70. Haemorrhoids (‘piles’) Haemorrhoids (piles) are engorged vascular cushions found within the submucosa of the anal canal that exist in three columns in the anal canal: •right anterolateral, • right posterolateral, •and left lateral.
- 72. Innervation • above dentate line and internal anal sphincter – Sympathetic L1,L2: from pelvic plexus ……. Cause contraction – parasympathetic S2,S3,S4( cause relaxsion )and afferent sensory: pelvic splanchnic nerves • below dentate line and external anal sphincter – inferior rectal branches of the pudendal nerve
- 73. last
- 76. SUMMARY • The anorectal area consists of a relatively small but complex region where multiple anatomic and physiologic interactions occur to help aid continence and defecation.
- 78. References • Short Practice Of Surgery Bailey & Love’s 26th Edition • Sabiston Textbook Of Surgery 20TH Edition • Schwartz’s Principles Of Surgery Tenth Edition • Netter’s Surgical Anatomy 2ND Edition • Clinical Anatmy BY Regions ,Snell 9TH Edition • Last Anatomy 2011 . • Cracking The Mrcs Viva 2007. • Slideshare ,Google .
Hinweis der Redaktion
- The anal canal is the most terminal part of the lower GI tract/large intestine, which lies between the anal verge (anal orifice, anus) in the perineum below and the rectum above.
- Posteriorly: The anococcygeal body, which is a mass of fibrous tissue lying between the anal canal and the coccyx Laterally: The fat-filled ischiorectal fossae Anteriorly: In the male,: the perineal body, the urogenital diaphragm, the membranous part of the urethra, and the bulb of the penis In the female, the perineal body, the urogenital diaphragm, and the lower part of the vagina.
- Imperforate anus is a congenital anomaly in which the anal canal fails (completely or incompletely) to open to the exterior. The rectum may also be abnormal (e.g., it may end blindly at a variable level). Various classifications of anorectal anomalies have been proposed.
- Pelvic Floor Muscles The levator ani muscle forms much of the floor of the pelvis. Traditionally the levator ani muscle has been thought to consist of 3 muscles: (1) the iliococcygeal muscle, (2) the pubococcygeal muscle, and (3) the puborectalis muscle. It supports the viscera of the pelvic cavity and aids in defecation with a coordinated action.
- The muscle derives its nerve supply from the sacral somatic nerves, and is functionally indistinct from the external anal sphincter. The position and length of the anal canal, as well as the angle of the anorectal junction, depend to a major extent on the integrity and strength of the puborectalis muscle sling. It gives off fibres that contribute to the longitudinal muscle layer.
- Schwartz’s Principles of Surgery Tenth Edition The internal and external sphincters are tonically active at rest The internal sphincter is responsible for most of the resting, involuntary sphincter tone (resting pressure). The external sphincter is responsible for most of the voluntary sphincter tone (squeeze pressure).
- External anal sphincter Composed of skeletal muscle and classically categorised into deep, superficial, and subcutaneous parts: deep part circular muscle fibres blends with puborectalis part of levator ani (posteriorly and laterally) the aforementioned region is called the anorectal ring, and is palpable on rectal examination superficial part elliptical muscle fibres attaches from the the tip of the coccyx posteriorly to the perineal body anteriorly only part of the sphincter with bony attachment subcutaneous part circular muscle fibres lower ends curve inwards, lying below the end of the internal sphincter, the intersphincteric groove that results is palpable on examination
- deep part circular muscle fibres blends with puborectalis part of levator ani (posteriorly and laterally) the aforementioned region is called the anorectal ring, and is palpable on rectal examination superficial part elliptical muscle fibres attaches from the the tip of the coccyx posteriorly to the perineal body anteriorly only part of the sphincter with bony attachment subcutaneous part circular muscle fibres lower ends curve inwards, lying below the end of the internal sphincter, the intersphincteric groove that results is palpable on examination
- This plane is important as it contains intersphincteric anal glands .and is also a route for the spread of pus, which occurs along the extensions from the longitudinal muscle layer.
- The longitudinal muscle The longitudinal muscle is a direct continuation of the smooth muscle of the outer muscle coat of the rectum, augmented in its upper part by striated muscle fibres originating from the medial components of the pelvic floor. Most of the muscle continues caudally before splitting into multiple terminal septa that surround the muscle bundles of the subcutaneous portion of the external sphincter to insert into the skin of the lowermost part of the anal canal and adjacent perianal skin.
- At the anorectal junction the outer longitudinal layer of rectal m. become fibro elastic and, together with some striated muscles fibres of puborectalis , forms he conjoint longitudinal coat which runs down between the two sphincters. Strands from this sheet penetrate the int. sphinter and the lower part of external sphincter, some reach the fat of ischioanal fossa and perianal skin, other pass through the internal sphin. To mucosa of anal canal.
- Three –quarters ¾* The circular muscle layer of the rectum continues distally to form the thickened and rounded internal sphincter, which terminates approximately 1.5 cm below the dentate line, just cephalad to the external sphincter (intersphincteric groove).sabiston20
- Although innervated by the autonomic nervous system, it receives intrinsic non-adrenergic and non-cholinergic (NANC) fibres, stimulation of which causes release of the neurotransmitter nitric oxide, which induces internal sphincter relaxation.
- The internal sphincter (involuntary) accounts for 80% of resting pressure, whereas the external sphincter (voluntary) accounts for 20% of resting pressure and 100% of squeeze pressure. The external anal sphincter contracts in response to sensed rectal contents and relaxes during defecation.
- DEFECATION Faeces arrive at the rectum from emptying of the distal large bowel, giving rise to the urge to defecate. The intra-abdominal pressure rises with increase in diaphragmatic and abdominal muscle pressures. Anal sphincters now voluntarily relax and the faeces are evacuated.
- Evaluation includes visual and digital examination observing for gross tone or squeeze abnormalities. Anal manometry quantitatively measures parameters of anal function, including resting and squeeze pressure (normal mean >40 and >80 mm Hg, respectively), sphincter length (4 cm in men, 3 cm in women), and minimal sensory volume of the rectum. Pudendal nerve terminal motor latency (PNTML) testing and endoanal ultrasound provide neural and anatomic information. TTT: Major defects require anal sphincter reconstruction, in which the anatomic sphincter defect is repaired. Artificial anal sphincters may be used in patients without a reconstructible native anal sphincter. Severe denervations of an intact anal sphincter may be managed with sacral nerve stimulation, artificial sphincters, or palliative diverting colostomy.
- This involuntary muscle commences where the rectum passes through the pelvic diaphragm and ends above the anal orifice, its lower border palpable at the intersphincteric groove, below which lie the most medial fibres of the subcutaneous external sphincter, and separated from it by the anal intermuscular septum.
- Between the columns of Morgagni are the anal crypts into which drain several anal glands
- The anal columns : are 5 to 10 vertical folds of mucosa separated by anal sinuses and valves; they contain portions of the rectal venous plexus Several vertical mucosal folds, the anal (formerly called rectal) columns, are usually visible in the upper half of the canal (fig. 36-1). The columns are vascular, and enlargement of their venous plexus results in internal hemorrhoids. The anal columns are united below by anal valves, which bound anal sinuses. The lower limit of the anal valves is the pectinate line, below which is a zone termed the pecten. The interval between the internal and external sphincters may be marked by a white line. The pecten merges with the skin of the anus. An ischiorectal abscess may drain through afistula in ano into the anal canal.
- The anal valves are small valve-like folds at the lower ends of the anal sinuses in the rectum. The anal valves join together the lower ends of the anal columns. The anal sinuses are furrows in the anal canal, that separate the anal columns from one another. The anal sinuses end below in small valve-like folds, termed anal valves.
- dentate line is a most important landmark both morphologically and surgically, representing the site of fusion of the proctodaeum and postallantoic gut, and being the site of the crypts of Morgagni (synonym: anal crypts, sinuses).
- The anal sinuses(the crypts of Morgagni) (rectal sinuses) are furrows in the anal canal, that separate the anal columns from one another. The anal sinuses end below in small valve-like folds, termed anal valves.
- The anal glands are located in the wall of the anal canal. They secrete into the anal canal via anal ducts which open into the anal crypts along the level of the dentate line. The glands themselves are located at varying depths in the anal canal wall, some in between the layers of the internal and external sphincter (the intersphincteric plane). The cryptoglandular theory states that obstruction of these ducts, presumably by accumulation of foreign material (e.g. fecal bacterial plugging) in the crypts, may lead to perianal abscess and fistula formation. Gray's Anatomy 80% are submucosal in extent, 8% extend to the internal sphincter, 8% to the longitudinal muscle, 2% to intersphincteric space, and 1% penetrate the external sphincter.
- Abscess Infection originates in the intersphincteric plane, most likely in one of the anal glands. This may result in a simple intersphincteric abscess or it may extend vertically upward or downward (Fig. 53-14), horizontally (Fig. 53-15), or circumferentially (Fig. 53-16), with varied clinical presentations.
- The pecten: is a smooth area of hairless stratified epithelium that lies between the anal valves superiorly and the inferior border of the internal anal sphincter inferiorly.
- Crrugator cutis ani
- baily Thomson: He was also able to show the presence of free communications between tributaries of the superior, middle and inferior rectal veins, as well as tiny direct arteriovenous communications with the submucosal venous dilatations. These communications have been shown both histologically and radiologically, and the oxygen tension of the blood contained within the venous dilatations (as well as the colour) is more arterial than venous.
- HEMORRHOIDS What are haemorrhoids? Haemorrhoids (piles) are engorged vascular cushions found within the submucosa of the anal canal. They consist of a sacculated venous plexus with a rich arterial supply supported by a fibromuscular connective tissue. are vascular and connective tissue cushions that exist in three columns in the anal canal: right anterolateral, right posterolateral, and left lateral. Internal hemorrhoids are above the dentate line and thus covered with mucosa. These may bleed and prolapse, but they do not cause pain. External hemorrhoids are below the dentate line and covered with anoderm. These do not bleed but may thrombose, which causes pain and itching, and secondary scarring may lead to skin tag formation. Hard stools, prolonged straining, increased abdominal pressure, and prolonged lack of support to the pelvic floor all contribute to the abnormal enlargement of hemorrhoidal tissue.
- The external sphincter, under voluntary control, is innervated by the inferior rectal branch of the internal pudendal nerve and perineal branch of the fourth sacral nerve. Thus, the loss of bilateral S3 nerve roots (either surgically or otherwise) will result in incontinence.sabiston
- Last anatomy:
- Lymphatic drainage above dentate line: internal iliac nodes below dentate line: superficial inguinal nodes Lymph from the upper half of the anal canal flows upwards to drain into the postrectal lymph nodes and from there goes to the para-aortic nodes via the inferior mesenteric chain. Lymph from the lower half of the anal canal drains on each side first into the superficial and then into the deep inguinal group of lymph glands.baily