Surgical Anatomy of Colon, Abdominal Vasculature, and Nerve Plexuses, Anal Canal PDF

Surgical Anatomy of (Colon, Abdominal vasculature and nerve plexuses, Anal canal) Prepared by Dr Ibrahim Mousa Maaroof Higher Diploma student M.B.Ch.B. Dr Sarmad Nadhem Ismael Higher Diploma student M.B.Ch.B. Supervised by Assist. Prof. Dr Baderkhan Saeed Ahmed Assist. Prof. Dr Azhy Muhammed Dewana...

Surgical Anatomy of (Colon, Abdominal vasculature and nerve plexuses, Anal canal) Prepared by Dr Ibrahim Mousa Maaroof Higher Diploma student M.B.Ch.B. Dr Sarmad Nadhem Ismael Higher Diploma student M.B.Ch.B. Supervised by Assist. Prof. Dr Baderkhan Saeed Ahmed Assist. Prof. Dr Azhy Muhammed Dewana 19 December 2023 1 COLON COLON • The colon (large intestine) is the distal part of the gastrointestinal tract, extending from the cecum to the anal canal. • It receives digested food from the small intestine, from which it absorbs water and electrolytes to form faeces. • Anatomically, the colon can be divided into four parts Of the four parts of the colon, the transverse and sigmoid parts are suspended in mesenteries • The ascending and descending colon are plastered on to the posterior abdominal wall. ASCENDING COLON • The ascending colon is about 13 cm long and lies in the right lower quadrant. • It’s a retroperitoneal structure which ascends superiorly from the cecum. • When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon. RELATIONS Anteriorly: Coils of small intestine, the greater omentum, and the anterior abdominal wall Posteriorly: The iliacus, the iliac crest, the quadratus lumborum, and the lower pole of the right kidney. The iliohypogastric and the ilioinguinal nerves cross behind it. • Blood Supply Arteries The ileocolic and right colic branches of the superior mesenteric artery supply this area. Veins The veins correspond to the arteries and drain into the superior mesenteric vein. • Lymph Drainage The lymph vessels drain into the superior mesenteric nodes. • Nerve Supply Sympathetic and parasympathetic (vagus) nerves from the superior mesenteric plexus supply this area of the colon. TRANSVERSE COLON • The transverse colon extends from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly. This turn is known as the left colic flexure. Here, the colon is attached to the diaphragm by the phrenicocolic ligament. • The transverse colon is the least fixed part of the colon, and is variable in position (it can dip into the pelvis in tall, thin individuals). Unlike the ascending and descending colon, the transverse colon is intraperitoneal and is enclosed by the transverse mesocolon. RELATIONS • Anteriorly: The greater omentum and the anterior abdominal wall (umbilical and hypogastric regions) • Posteriorly: The second part of the duodenum, the head of the pancreas, and the coils of the jejunum and the ileum Blood Supply • Arteries The proximal two thirds are supplied by the middle colic artery, a branch of the superior mesenteric artery The distal third is supplied by the left colic artery, a branch of the inferior mesenteric artery. • Veins The veins correspond to the arteries and drain into the superior and inferior mesenteric veins. Lymph Drainage • The proximal two thirds drain into the superior mesenteric nodes; the distal third drains into the inferior mesenteric nodes. Nerve Supply • The proximal two thirds are innervated by sympathetic and vagal nerves through the superior mesenteric plexus, distal third is through the inferior mesenteric plexus. DESCENDING COLON • After the left colic flexure, the colon moves inferiorly towards the pelvis – and is called the descending colon. It is retroperitoneal in the majority of individuals, but is located anteriorly to the left kidney, passing over its lateral border. • Lies in the left upper and lower quadrants • Extends downward from the left colic flexure, to the pelvic brim, • Where it begins to turn medially, it becomes the sigmoid colon. RELATIONS • Anteriorly: Coils of small intestine, the greater omentum, and the anterior abdominal wall • Posteriorly: The lateral border of the left kidney, the quadratus lumborum, the iliac crest, and the left psoas Blood Supply • Arteries The left colic and the sigmoid branches of the inferior mesenteric artery • Veins The veins correspond to the arteries and drain into the inferior mesenteric vein. Lymph Drainage • Lymph drains into the inferior mesenteric nodes around the origin of the inferior mesenteric artery. Nerve Supply • The nerve supply is the sympathetic and parasympathetic nerves through the inferior mesenteric plexus. SIGMOID COLON • The 40cm long sigmoid colon is located in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of the S3 vertebra. This journey gives the sigmoid colon its characteristic “S” shape. • The sigmoid colon is attached to the posterior pelvic wall by a mesentery – the sigmoid mesocolon. The long length of the mesentery permits this part of the colon to be particularly mobile. RELATIONS • Anteriorly: In the male, the urinary bladder; in the female, the posterior surface of the uterus and the upper part of the vagina • Posteriorly: The rectum and the sacrum. The sigmoid colon is also related to the lower coils of the terminal part of the ileum. Blood Supply • Arteries Sigmoid branches of the inferior mesenteric artery. • Veins The veins drain into the inferior mesenteric vein, which joins the portal venous system. Lymph Drainage • The lymph drains into nodes along the course of the sigmoid arteries; to the inferior mesenteric nodes. Nerve Supply • The sympathetic and parasympathetic nerves from the inferior hypogastric plexuses THE RECTUM • is the most distal segment of the large intestine, and has an important role as a temporary store of faeces. • It is continuous proximally with the sigmoid colon (S3), and terminates into the anal canal. • It passes downward, following the curve of the sacrum and coccyx, and ends in front of the tip of the coccyx. • The lower part of the rectum is dilated to form the rectal ampulla • The puborectalis portion of the levator ani muscles forms a sling at the junction of the rectum with the anal canal and pulls this part of the bowel forward, producing the anorectal angle. • The peritoneum covers the anterior and lateral surfaces of the first third of the rectum and only the anterior surface of the middle third, leaving the lower third devoid of peritoneum 19 December 2023 19 RELATIONS • Posteriorly: The rectum is in contact with the sacrum and coccyx, and levatores ani muscles; the sacral plexus; and the sympathetic trunks • Anteriorly: In the male, the upper two thirds of the rectum, is related to the sigmoid colon and coils of ileum that occupy the rectovesical pouch. The lower third of the rectum is related to the posterior surface of the bladder, vas deferens and the seminal vesicles on each side, and to the prostate In the female, the upper two thirds of the rectum, is related to the sigmoid colon and coils of ileum that occupy the rectouterine pouch. The lower third of the rectum, is related to the posterior surface of the vagina. BLOOD SUPPLY • Arteries The superior, middle, and inferior rectal arteries supply the rectum. • The superior rectal artery is a direct continuation of the inferior mesenteric artery and is the chief artery supplying the mucous membrane. • The middle rectal artery is a small branch of the internal iliac artery and is distributed mainly to the muscular coat. • The inferior rectal artery is a branch of the internal pudendal artery in the perineum. It anastomoses with the middle rectal artery at the anorectal junction. • VEINS The veins of the rectum correspond to the arteries. The superior rectal vein is a tributary of the portal circulation and drains into the inferior mesenteric vein. The middle and inferior rectal veins drain into the internal iliac and internal pudendal veins, respectively Lymph Drainage • The lymph vessels of the rectum drain first into the pararectal nodes and then into inferior mesenteric nodes. • Lymph vessels from the lower part of the rectum follow the middle rectal artery to the internal iliac nodes. Nerve Supply • The nerve supply is from the sympathetic and parasympathetic nerves from the inferior hypogastric plexuses. The rectum is sensitive only to stretch. ABDOMINAL VASCULATURE ABDOMINAL AORTA • The abdominal aorta is a continuation of the thoracic aorta beginning at the level of the T12 vertebrae. It is approximately 13cm long and ends at the level of the L4 vertebra. At this level, the aorta terminates by bifurcating into the right and left common iliac arteries that supply the lower body. BRANCHES IN DESCENDING ORDER • Inferior phrenic arteries: Paired parietal arteries arising posteriorly at the level of T12. They supply the diaphragm. • Coeliac artery: A large, unpaired visceral artery arising anteriorly. It is also known as the celiac trunk and supplies the liver, stomach, abdominal oesophagus, spleen, the superior duodenum and the superior pancreas. • Superior mesenteric artery: A large, unpaired visceral artery arising anteriorly, just below the celiac artery. It supplies the distal duodenum, jejuno-ileum, ascending colon and part of the transverse colon. It arises at the lower level of L1. • Middle suprarenal arteries: Small paired visceral arteries that arise either side posteriorly to supply the adrenal glands. • Renal arteries: Paired visceral arteries that arise laterally at the level between L1 and L2. They supply the kidneys. • Gonadal arteries: Paired visceral arteries that arise laterally. Note that the male gonadal artery is referred to as the testicular artery and in females, the ovarian artery. • Inferior mesenteric artery: A large, unpaired visceral artery that arises anteriorly at the level of L3. It supplies the large intestine from the splenic flexure to the upper part of the rectum. • Median sacral artery: An unpaired parietal artery that arises posteriorly to supply the coccyx, lumbar vertebrae and the sacrum. • Lumbar arteries: There are four pairs of parietal lumbar arteries that arise postero-laterally between the levels of L1 and L4 to supply the abdominal wall and spinal cord. INFERIOR VENA CAVA • The inferior vena cava is the common convergence of venous drainage from all structures below the diaphragm. It is located on the posterior abdominal wall; anteriorly to the vertebral column and to the right of the abdominal aorta. • The vessel is formed by the union of the common iliac veins at the L5 vertebral level. It ascends superiorly, and leaves the abdomen by piercing the central tendon of the diaphragm at the T8 level (the caval hiatus). Within the thorax, the inferior vena cava drains into the right atrium of the heart. TRIBUTARIES The inferior vena cava is responsible for the venous drainage of all structures below the diaphragm. It receives tributaries from: • Common iliac veins – formed by the external and internal iliac veins. They drain the lower limbs and gluteal region. • Lumbar veins – drain the posterior abdominal wall. • Renal veins – drain the kidneys, left adrenal gland and left testis/ovary. • Right testicular or ovarian vein – drains the right testes in males and the right ovary in females (the left testicular or ovarian vein drains into the left renal vein). • Right suprarenal vein – drains the right adrenal gland (the left adrenal vein drains into the left renal vein). • Inferior phrenic veins – drain the diaphragm. • Hepatic veins – drain the liver. There are no tributaries from the spleen, pancreas, gallbladder or the abdominal part of the GI tract – as these structures are first drained into the portal venous system. However, venous return from these structures ultimately enters the inferior vena cava via the hepatic veins (after being processed by the liver). URETERS • The ureter is 25 cm long. Its points of narrowest caliber are at the pelviureteric junction and as it passes through the bladder wall. • The ureter passes down on psoas major under cover of the peritoneum and crosses in front of the genitofemoral nerve, being itself crossed anteriorly by the gonadal vessels • On the right the upper part is behind the third part of the duodenum, while lower down it is crossed anteriorly by the right colic and ileocolic vessels and by the root of the mesentery • On the left it is lateral to the inferior mesenteric vessels and is crossed anteriorly by the left colic vessels • It leaves the psoas muscle at the bifurcation of the common iliac artery, over the sacroiliac joint, and passes into the pelvis. • It can be distinguished from vessels and nerves in the living body in that it is a whitish, non-pulsatile cord which shows peristaltic activity when gently pinched with forceps. Ureters THE LUMBOSACRAL PLEXUS • is a network of nerve fibers, derived from the roots of lumbar and sacral spinal nerves that branch out to form the nerves supplying the lower limb. • In the human body, there are 31 pairs of spinal nerves corresponding to a segment of the vertebral column is formed by the anterior rami of spine • It is located on the posterolateral wall of the pelvis, adjacent to the lumbar spine. The lumbosacral plexus then embeds itself into the psoas major muscle and later emerges in the pelvis. PELVIC BLOOD SUPPLY • The pelvic cavity contains the organs of reproduction, urinary bladder, pelvic colon, rectum and numerous muscles. Its arterial supply is largely via the internal iliac artery, with some smaller arteries providing additional supply. THE INTERNAL ILIAC ARTERY • Is the major artery of the pelvis. It originates at the bifurcation of the common iliac artery into its internal and external branches. This approximately occurs at vertebral level L5. • The artery descends inferiorly, crossing the pelvic inlet to enter the pelvis. During its descent, it is situated medially to the external iliac vein and obturator nerve. At the superior border of the greater sciatic foramen, it divides into anterior and posterior trunks. ANTERIOR TRUNK The anterior trunk gives rise to numerous branches that supply the pelvic organs, the perineum, and the gluteal and adductor regions of the lower limb. The following branches of the internal iliac • Obturator artery – Travels through the obturator canal, accompanied by the obturator nerve and vein. It supplies the muscles of the thigh’s adductor region. • Umbilical artery – Gives rise to the superior vesical artery, which supplies the superior aspect of the urinary bladder. • Inferior vesical artery – Supplies the lower aspect of the bladder. In males, it also supplies the prostate gland and seminal vesicles. • Vaginal artery (female) – Descends to the vagina, supplying additional branches to the inferior bladder and rectum. • Uterine artery (female)– Travels within the cardinal ligament to reach the cervix, where it ascends along the lateral aspect of the uterus. At origin of the fallopian tubes, it anastomoses with the ovarian artery. • Middle rectal artery – Travels medially to supply the distal part of the rectum. It also forms anastomoses with the superior rectal artery (derived from the inferior mesenteric) and the inferior rectal artery (derived from the internal pudendal) • Internal pudendal artery – Moves inferiorly to exit the pelvis via the greater sciatic foramen. Accompanied by the pudendal nerve, it then enters the perineum via the lesser sciatic foramen. It is the main artery responsible for the blood supply to the perineum. • Inferior gluteal artery – The terminal branch of the anterior trunk. It leaves the pelvic cavity via the greater sciatic foramen, emerging inferiorly to the piriformis muscle in the gluteal region. It contributes to the blood supply of the gluteal muscles and hip joint. POSTERIOR TRUNK The posterior trunk gives rise to arteries that supply the lower posterior abdominal wall, posterior pelvic wall and the gluteal region. There are typically three branches: • Iliolumbar artery – Ascends to exit the pelvis, dividing into a lumbar and iliac branch. • Lateral sacral arteries (superior and inferior) supply structures in the sacral canal, and the skin and muscle posterior to the sacrum. • Superior gluteal artery – The terminal branch of the posterior trunk.It is the major blood supply to the muscles and skin of the gluteal region. ANAL CANAL ANAL CANAL • The anal canal is the final segment of the gastrointestinal tract. • It has an important role in defecation and maintaining faecal continence. Anatomical Position • The anal canal is located within the anal triangle of the perineum between the right and left ischioanal fossae. It is the final segment of the gastrointestinal tract, around 4cm in length. • The canal begins as a continuation of the rectum and passes inferoposteriorly to terminate at the anus. 19 December 2023 48 ANATOMICAL STRUCTURE Except during defecation, the anal canal is collapsed by the internal and external anal sphincters to prevent the passage of faecal material. Anal Sphincters The anal canal is surrounded by internal and external anal sphincters, which play a crucial role in the maintenance of faecal continence: • Internal anal sphincter – surrounds the upper 2/3 of the anal canal. It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall. • External anal sphincter – voluntary muscle that surrounds the lower 2/3 of the anal canal (and so overlaps with the internal sphincter). It blends superiorly with the puborectalis muscle of the pelvic floor. 19 December 2023 49 • The external anal sphincter is divided into three parts: • Subcutaneous • Superficial, which is attached to the coccyx behind and the perineal body in front • Deep, which is continuous with the puborectalis part of levator ani. • The deep part of the external sphincter where it blends with levator ani together with the internal anal sphincter is termed the anorectal ring. • The anorectal ring is palpable with a finger in the anal canal where it forms a ring, immediately above which the finger enters the ampulla of the rectum. 19 December 2023 50 The subcutaneous part of the external anal sphincter is traversed by a fan-shaped expansion of longitudinal muscle fibres of the anal canal. The nerve supply of the external sphincter is via the inferior rectal branch and the pudendal nerve (S2, S3) and the perineal branch of S4. 19 December 2023 51 INTERNAL STRUCTURE • The superior aspect of the anal canal has the same epithelial lining as the rectum (columnar epithelium). • However, in the anal canal, the mucosa is organised into longitudinal folds, known as anal columns. • These are joined at their inferior ends by anal valves. • Above the anal valves are small pouches which are referred to as anal sinuses – these contain glands that secrete mucus. • The anal valves collectively form an irregular circle – known as the pectinate line (or dentate line). 19 December 2023 52 This line divides the anal canal into upper and lower parts, which differ in both structure and neurovascular supply. This is a result of their different embryological origins: • Above the pectinate line – derived from the embryonic hindgut. • Below the pectinate line – derived from the ectoderm. • Inferior to the pectinate line, the anal canal is lined by non-keratinised stratified squamous epithelium (known as the anal pecten). It is a pale and smooth surface, which transitions at the level of the intersphincteric groove to true skin (keratinised stratified squamous). 19 December 2023 53 19 December 2023 54 ANATOMICAL RELATIONS • The anal canal lies in close proximity to several other important structures in the pelvis and perineum: 19 December 2023 55 NEUROVASCULA R SUPPLY AND LYMPHATICS As discussed above, the pectinate line divides the anal canal into two parts – which have a different arterial supply, venous drainage, innervation and lymphatic drainage. 19 December 2023 56 DIGITAL RECTAL EXAMINATION The following structures can be palpated by the finger passed per rectum in the normal patient. • Both sexes: o o o o o anorectal ring coccyx sacrum ischiorectal fossae ischial spines. • Male: o prostate o rarely, the seminal vesicles. • Female: o perineal body o cervix o occasionally, the ovaries. 19 December 2023 57 The following abnormalities can also be detected. • Lumen: o faecal impaction o foreign bodies. • In the wall: o rectal tumours o rectal strictures o thrombosed haemorrhoids (haemorrhoids are not palpable unless thrombosed). • Outside rectal wall: o prostatic abnormalities o abnormalities of the uterine cervix o ovarian enlargement o masses in the pouch of Douglas o tenderness in the pouch of Douglas with peritonitis o pelvic bony tumours o foreign bodies in the vagina, e.g. tampon, pessary or others. 19 December 2023 58 ISCHIORECTAL FOSSA This is a space between the anal canal and side wall of the pelvis. Its boundaries are: • medially: fascia over levator ani and the external anal sphincter • laterally: fascia over obturator internus • anteriorly: extends forwards as a prolongation deep to the urogenital diaphragm • posteriorly: limited by the sacrotuberous ligaments and the origin of gluteus maximus from this ligament. 19 December 2023 59 19 December 2023 60 REFERENCES • O'Connell, P.R., McCaskie, A.W., & Sayers, R.D. (Eds.). (2023). Bailey & Love's Short Practice of Surgery - 28th Edition • Brunicardi F, & Andersen D.K., & Billiar T.R., & Dunn D.L., & Kao L.S., & Hunter J.G., & Matthews J.B., & Pollock R.E.(Eds.), (2019). Schwartz's Principles of Surgery, 11e. 19 December 2023 61 Thank You 19 December 2023 62