Anatomy and Embryology of General Surgery: Colon, Rectum and Anal Canal

1. Kingdom of BahrainArabian Gulf UniversityCollege of Medicine and Medical Sciences General Surgery Colon, Rectum and Anal Canal Ali Jassim Alhashli

2. Anatomy and Embryology • Embryology: • Midgut: from ampulla of Vater to mid-transverse colon. Midgut is supplied by SMA. • Hindgut: rest of the colon to proximal anus. Hindgut is supplied by IMA. • Distal anus from ectoderm. Blood supply from branches of internal pudendal artery. • Dentate line marks the transition between proximal anus and ectoderm. • Anatomy: • Colon: • It extends from ileocecal valve to the rectum and consists of: cecum, ascending colon, transverse colon, descending colon and sigmoid colon (1-1.5 meters in length). • Colon is characterized by the presence of: • Haustra • Taenia coli: 2 distinct bands of longitudinal muscle converging at the appendix. • Fat appendages. • Intraperitonealvs retroperitoneal parts of the colon: • Intraperitoneal: cecum, transverse colon and sigmoid colon. • Retroperitoneal: ascending colon, descending colon and posterior parts of hepatic and splenic flexures.

3. Anatomy and Embryology

4. Anatomy and Embryology • Anatomy (continued): • Rectum: • Length: 15 cm. • Fascia: • Waldeyer’s fascia: extending from S4 vertebra (in sacrum) to the rectum. • Denovillier’s fascia: anterior to lower third of the rectum. • Pelvic floor: • Formed by levatorani which is composed of the following muscle: pubococcygeus, iliococcygeus and puborectalis. Levatorani is innervated by S4. • Anus: • Anal canal extends from pelvic floor to anal verge (junction between anoderm and perianal skin). • Dentate line: separates proxminal anus in which epithelium is columnar from distal anus in which the epitheliam is squamous (from ectoderm). • Columns of Morgagni: 12-14 columns, superior to dentate line, separated by crypts, perianal glands discharge their secretions at the base of these columns. • Anal sphincter: • Internal anal sphincter: made of smooth muscle, involuntary, contracted at rest. • External anal sphincter: made of striated muscle, voluntary.

5. Anatomy and Embryology

6. Anatomy and Embryology • Blood supply: • Arterial supply: • SMA: • Supplies cecum, ascending colon and proximal 2/3 of transverse colon. • Via: ileocolic, right colic and middle colic arteries. • IMA: • Supplies: distal third of transverse colon, descending colon, sigmoid colon and superior rectum. • Via: left colic, sigmoidal and superior rectal arteries. • Notice that splenic flexure represents “watershed” area between the areas supplied by SMA and IMA. • Internal iliac artery: • Supplies: middle and distal rectum. • Via: middle and inferior rectal arteries. • Internal pudendal artery: • Supplies the anus. • Venous drainage: • SMV: drains cecum, ascending colon and transverse colon. • IMV: drains descending colon, sigmoid colon and superior rectum. • Internal iliac veins: drain middle and inferior rectum. • Middle rectal vein: drains upper anus. • Inferior rectal vein: drains lower anus.

7. Anatomy and Embryology

8. Anatomy and Embryology • Innervation: • Sympathetic: inhibits peristalsis. • Parasympathetic: stimulates peristalsis. • Lymphatic drainage of anal canal: • Above dentate line: internal iliac lymph nodes. • Below dentate line: inguinal lymph nodes. • Histology: • Colon and rectum: mucosa, submucosa, inner circular muscle layer and outer longitudinal muscle layer. • Anus: anoderm.

9. Physiology • What are the functions of colon and rectum? • Absorption of water and electrolytes from stool. • Storage of feces. • Motility: • Segmental contraction (most common): localized simultaneous contractions of longitudinal and circular muscle of the colon. • Retrograde movement (from transverse colon to cecum): prolonging the time of presence of colon contents to increase the absorption of water and electrolytes. • Mass movement: • Antegrade propulsion of luminal contents. • Duration = 30 seconds, frequency: 3-4 times/day (especially after waking up or eating), rate = 0.5-1 cm/second. • Neuronal control of the colon: • Extrinsic: sympathetic and parasympathetic. • Intrinsic: Meissner’s plexus and Auerbach’s plexus. • Process of defecation: • Mass movement will push feces to be stored in the rectum. • Rectum will distend causing relaxation of internal sphincter. • Relaxation of external sphincter leads to propulsion of feces through anal canal. • Increased intra-abdominal pressure aids in the propulsion of feces.

10. Physiology

11. Irritable bowel syndrome: characterized by • Abdominal pain. • Alternating diarrhea and constipation for 3 months. • Abdominal pain relieved by defecation. • Constipation: • Definition: passing > 3 stools/week. • Types: • Acute constipation: > 3 months. • Chronic constipation: < 3 months. Obstipation: it is constipation and inability to pass flatus (gas) and it is considered to be an indication of obstruction. • Causes: • Lack of enough fluid intake and dietary fibers. • Lack of physical activity. • Hypothyroidism. • Medications (such as opiates). • Neurologic disease (Parkinson’s disease and multiple sclerosis). • Treatment: • Change diet: by increasing fluids and fibers. • Physical activity. • Stool softeners. • Diarrhea: • Definition: passing < 3 loose stools/day. • Causes: infectious, ischemic, neurologic disruption, short-bowel syndrome or complication of gastric bypass surgery. • Diagnosis: • Stool sample for: leukocytes, culture, occult blood and fat content. • Chronic diarrhea: colonoscopy + biopsy. • Treatment: depending on the cause. Disorders of Motility

12. Pseudomembranous colitis: • Definition: it is the acute inflammation of the colon which is characterized by the formation of pseudomembranes at sites of mucosal injury. It usually occurs after administrating broad-spectrum antibiotics (especially clindamycin). • Cause: Clostridium difficile (Gram +, anaerobic and spore-forming organism). • Signs and symptoms: diarrhea. • Diagnosis: • Detection of C.difficile toxin in stool. • Colonoscopy (if you are not sure about your diagnosis). • Treatment: metronidazole. • Ischemic colitis: • Definition: acute or chronic ischemia of the colon which occurs due to hypoperfusion (splenic flexure most commonly affected) or due to embolus/thrombosis of IMA. It is commonly seen among elderly. • Risk factors: • Old age. • Atrial fibrillation. • Hyperocoagulation status. • Post abdominal aortic aneurysm repair. • HTN. • Sickle cells disease. • Signs and symptoms: • Mild lower abdominal pain. • Rectal bleeding. • Diagnosis: • AXR: pneumatosis (air in bowel wall) + thumbprinting (indicating the presence of submucosal edema). • CT-scan: thickened bowel wall. • Colonoscopy: pale muscoa with petechial bleeding. • Treatment: • Mild: IV fluids and observe. • Moderate (with fever and leukocytosis): IV fluids + IV antibiotics. • Severe (with peritoneal signs): exploratory laparotomy with colostomy. Colitis

13. Colitis Thumb-printing sign Pneumatosis

14. Ulcerative colitis: • Definition: it is an inflammatory bowel disease which exclusively affects the colon. Inflammation is limited to the mucosa (not transmural), continuous (no skip lesions) and usually starting from the rectum. It is thought to be due to autoimmune process. • Risk factors: • Positive family history. • Jewish descent. • White race. • Urban dwelling السكن الحضري • Notice that smoking is a PROTECTING factor against ulcerative colitis (in contrast to Crohn’s disease). • Signs and symptoms: • Abdominal pain and bloody diarrhea (more common than Crohn’s disease). • Diagnosis: • Barium: lead-pipe appearance (NO LONGER TEST OF CHOICE). • Sigmoidoscopy + biopsy. • Treatment: • Medical (similar to Crohn’s disease): • Mild/moderate disease: corticosteroids or salicylates. • Severe disease: IV steroids. • Refractory disease: immunosuppression (azathioprine/infliximab). • Surgery (it is curative unlike in Crohn’s disease): • Indications: increased risk of cancer with long-standing disease, bleeding and perforation. • Procedure: proctocolectomy (surgical removal of rectum and all/part of colon) with end ileostomy. Colitis

15. Colitis

16. Definitions: • Diverticula: outpouching of mucosa through muscular layer of bowel wall. • Diverticulosis: presence of numerous diverticulae. • Diverticulitis: inflammation of diverticula. Diverticular disease commonly affects sigmoid colon. • Risk factors: • Old age. • Low dietary fibers. • Signs and symptoms: • Diverticulosis: 80% of patients are ASYMPTOMATIC; symptomatic patients commonly present with PAINLESS, MASSIVE LOWER GI BLEEDING. • Diverticulitis: • LLQ abdominal pain. • Fever and leukocytosis. • Anorexia and nausea/vomiting. • Diagnosis: • Diverticulosis: barium enema or colonoscopy. • Diverticulitis: CT-scan (barium enema and colonoscopy are contraindicated due to the high risk of perforation). • Treatment: • Uncomplicated diverticulitis: • Outpatient management: analgesia, oral antibiotics and clear liquid diet. • Inpatient management (when outpatient therapy fails): IV hydration, IV antibiotics and bowel rest. • Complicated diverticulitis: • Hinchey’s staging system: • Stage-I: Colonic inflammation with pericolic abscess. • Stage-II: colonic inflammation with retroperitoneal or pelvic abscess. • Stage-III: purulent peritonitis. • Stage-IV: fecal peritonitis. • Treatment of Stage-I and II: CT-guided aspiration + IV antibiotics. • Treatment of Stage-III and IV: operative management. Diverticular Disease

17. Diverticular Disease Diverticulosis barium Diverticulosis colonoscopy Diverticulitis CT-scan

18. Lower GI Bleeding • Definition: it is bleeding which occurs distal to ligament of Treitz. • Causes: • Most common: diverticulosis and angiodysplasia. • Others: cancer, hemorrhoids, IBD and ischemic colitis. • Diagnosis: identify the site of bleeding • Colonoscopy. • Rate of bleeding ≥ 0.5 ml/minute → bleeding scan with Tc-sulfur colloid. • Rate of bleeding ≥ 1 ml/minute → angiography. • Treatment: • IV fluids and blood units (as needed). • If the site of bleeding is identified, your options are: octreotide, vasoconstrictiion with epinephrine, cautery with heat or embolizations. • If the site of bleeding is not identified or bleeding is massive and patient is unstable: laparotomy with possible resection of the affected segment of bowel.

19. Large Bowel Obstruction • Epidemiology: • It occurs in elderly. • It is less common than SBO. • The 3 most common causes of large bowel obstruction are: • Adenocarcinoma (65%). • Scarring secondary to diverticulitis (20%). • Volvulus (5%). • Signs and symptoms: • Abdominal distention. • Crampy abdominal pain. • Constipation/obstipation. • Nausea/vomiting. • Diagnosis: • Supine and upright AXR: air-fluid levels, air proximal to site of obstruction, lack of air distal to the site of obstruction. • Treatment: • NPO and NG tube (although it will not decompress the colon). • IV fluids and electrolytes. • Broad-spectrum antibiotics. • Relieve obstruction surgically.

20. Volvulus of Large Bowel • Definition: twisting of a segment of large bowel around its mesenteric axis especially occurring in elderly. • Location: • Most common: sigmoid (75%). • Cecum (25%). • Risk factors: • Old age. • Chronic constipation. • Hypermobilececum. • Psychotropic drugs. • Signs and symptoms: • Abdominal distention. • Crampy abdominal pain. • Constipation/obstipation. • Nausea and vomiting. • Diagnosis: • AXR: kidney bean appearance. • Barium enema: bird’s beak at areas of colonic narrowing. • Treatment: • Cecalvolvulus: right hemicolectomy. • Sigmoid volvulus: • Acute setting: decompression with rigid sigmoidoscopy. • Surgery (emergent if there is strangulation of perforation)

21. Pseudo-Obstruction of Large Bowel (Ogilvie Syndrome) • Definition: massive colonic dilation without evidence of mechanical obstruction which especially occurs in elderly. • Risk factors: • Severe infection. • Recent surgery or trauma. • Polypharmacy (especially antipsychotics). • Signs and symptoms: • Abdominal distention. • Mild abdominal pain. • Decreased/absent bowel sounds. • Diagnosis: • AXR: massive colonic distention. • Exclude mechanical cause of obstruction by: colonoscopy/barium enema. • Treatment: • NPO, NG tube and rectal tube (for both proximal and distal decompression). • IV fluid and electrolytes. • Stop offending medications. • Pharmacological decompression with neostigmine (alternative: colonoscopic decompression). • If peritoneal signs develop: exploratory laparotomy (for possible perforation).

22. Benign Tumors of Large Bowel • Colorectal polyps: • Morphological classification: • Sessile (flat). • Pedunculated (on a stalk). • Histological classification: • Inflammatory: ulcerative colitis. • Lymphoid: no malignant potential. • Hyperplastic: overgrowth of normal tissue; no malignant potential. • Adenomatous: considered to be pre-malignant; further classified to: tubular (75%), tubulovillous (15%) and villous (10%). • Hamatomatous: normal tissue arranged in abnormal configuration. • Malignant potential of a poly is determined by: • Size: < 2 cm. • Histology: villous. • Epithelial dysplasia: severe. • Signs and symptoms: • Most are ASYMPTOMATIC. • Melena/hematochezia. • Change in bowel habits (and it large enough it can result in obstruction). • Diagnosis: colonoscopy. • Treatment: removal of polyp by colonoscopy → if not possible → surgery (segmental colon resection).

23. Polyposis syndromes: Benign Tumors of Large Bowel

24. Epidemiology: • It is the 2nd most common cause of cancer deaths (after lung cancer). • Incidence increases with increasing age. • Risk factors: • Increased age (< 50 years). • Positive family history or past history of colon cancer. • Diet high in red meat and low in fibers. • Smoking. • Inherited polyposis syndromes. • Long-standing Crohn’s disease or ulcerative colitis. • Screening: • Patient is of average risk → starting from age of 50 years • Fecal Occult Blood Test annually. • Flexible sigmoidoscopy every 5 years. • Colonoscopy every 10 years. • Patient has a positive family history of colon cancer in a first-degree relative: starting 10 years before the age of the youngest affected relative: • Colonoscopy every 5 years. • Pathophysiology (adenoma-carcinoma sequence): • Normal mucosa of colon → hyperproliferation (APC gene loss/mutation and/or loss of DNA methylation) → early adenoma (Ras gene mutation) → intermediate adenoma → late adenoma (loss of DCC and p53 genes). Colorectal Carcinoma

25. Colorectal Carcinoma

26. Signs and symptoms: • Right-sided colon cancer: occult bleeding and anemia. • Left-sided colon cancer: rectal bleeding, obstructive symptoms and change of stool caliber. • Both: anorexia and weight loss. • Diagnosis: • Colon cancer: colonoscopy. • Rectal cancer: proctoscopy. • Staging (TNM): Colorectal Carcinoma

27. Staging (continued): • Stage-I: T1/T2, N0, M0 • Stage-II: T3/T4, N0, M0 • Stage-III: nodal disease. • Stage-IV: distant metastasis. • Treatment: • Surgical resection of the affected segment of colon with its lymphatics (once there is lymphatic involvement –stage III- chemotherapy with 5-FU is indicated): • Cecum or right colon: right hemicolectomy (removal of terminal ileum, cecum, ascending colon and proximal transverse colon). • Proximal/mid transverse colon: extended right hemicolectomy (same as right hemicolectomy + resection of remaining of transverse colon and splenic flexure). • Splenic flexure and left colon: left hemicolectomy (removal of distal transverse colon, descending colon and sigmoid colon). • Sigmoid: sigmoid colectomy. • Proximal rectum: low anterior resection. • Distal rectum: abdominal perineal resection. Colorectal Carcinoma

28. Colorectal Carcinoma

29. Hemorrhoids: • Definition: prolapse of submucosal veins in left lateral, right anterior and right posterior quadrants of anal canal. • Types: • Internal hemorrhoids: above dentate line; covered by columnar epithelium; PAINLESS • External hemorrhoids: below dentate line; covered by anoderm; PAINFUL • Grades: • Grade-I: protrusion through lumen; no prolapse; bleeding. • Grade-II: prolapse with straining; spontaneous return; bleeding. • Grade-III: manual reduction of prolapse, bleeding and pruritis. • Grade-IV:prolapse which cannot be reduced, bleeding and pruritis. • Risk factors: • Constipation. • Portal hypertension. • Pregnancy. • Increased pelvic pressure (ascites, tumor). • Diagnosis: history, Physical examination and visualization with anoscope. • Treatment: • Grades I, II and III → non-resectional measures (rubber-band ligation or injection sclerotherapy). • Grade IV → surgical excision. Perianal and Anal Problems

30. Perianal and Anal Problems

31. Anal fissure: • Definition: it is a linear tear in midline of posterior aspect of anal canal below the dentate line. • Causes: chronic constipation or excessive diarrhea. • Signs and symptoms: • Pain with defecation and sitting. • Bright red blood (hematochezia). • Extreme pain on digital rectal examination (patient will not allow you to examine him) and there is a visible tear. • Diagnosis: history and physical examination. • Treatment: • Sitz bath. • Stool softners (for chronic constipation) + increased fluid intake. • Topical nifedipine or nitroglycerine ointment. • Botulinum toxin injection. • Lateral internal sphincterotomy. • Anorectal abscess: • Definition: obstruction of anal crepts resulting in bacterial overgrowth. • Types: perianal, intersphincteric, ischiorectal and supralevator. • Risk factors: • Constipation/diarrhea/IBD. • Immunocompromised status. • Previous history of anorectal abscess. • Signs and symptoms: • Fever and leukocytosis. • Rectal pain of sudden onset. • Perianal area: erythema, swelling and warmth. • Treatment: surgical drainage and antibiotics. Perianal and Anal Problems

32. Perianal and Anal Problems

33. Anorectal fistulas • Definition: a fistula is an abnormal comminucation between two epithelialized surfaces. Anorectal fistulas originate from glands of anal canal at the dentate line (usually as a complication of anorectal abscess). • Types of anorectal fistulas: • Intersphincteric (most common). • Transsphincteric. • Suprasphincteric. • Extrasphincteric. • Signs and symptoms: • Recurrent or persistent perianal drainage. • It becomes painful if occluded. • Diagnosis: • Digital rectal examination. • Anoscopy. • If internal opening cannot be identified, inject methylene blue or hydrogen peroxide in the external opening of the fistula. • Treatment: • Unroofing of the entire tract of the fistula with or without placement of setons. • Goodsall’s rule: can be used to clinically predict the course of an anorectal fistula tract. Imagine a line that bisects the anus in the coronal plane. Any fistula that originates anterior to the line will course anteriorly in a direct route. Fistulae that originate posterior to the line will have a curved path. Perianal and Anal Problems

34. Perianal and Anal Problems

35. Pilonidal Disease • Definition: it is a cystic inflammation at the upper edge of gluteal cleft caused by trauma to her follicles which result in subsequent infection. • Epidemiology: • More common among hairy males. • Occurring from late teens to the 3rd decade. • Signs and symptoms: • Acute: presenting as an abscess. • Chronic: presenting as a draining sinus. • There is pain in gluteal area. • Treatment: • Acute presentation (abscess): incision and drainage under local anesthesia (with removal of hair) + antibiotics. • Chronic presentation (draining sinus): excision of the cyst and its tract.

36. Pilonidal Disease

37. Anorectal Cancer • Rare! • Risk factors: • Anal intercourse. • Multiple sexual partners. • HIV or HPV. • Immunocompromised status. • Smoking. • Signs and symptoms: • Often ASYMPTOMATIC. • If symptomatic: bleeding, lump and itching. • Diagnosis: biopsy with histopathologic evaluation • Tumors of perianal skin: squamous cell carcinoma, basal cell carcinoma, Paget’s disease or Bowen’s disease. • Tumors of anal canal: epidermoid (squamous cell carcinoma, transitional cell carcinoma) or malignant melanoma. • Staging: CXR, abdomino-pelvic CT-scan and LFT. • Treatment: • Tumors of perianal skin: wide local excision ± chemotherapy/radiation. • Tumors of anal canal: chemotherapy (5-FU and mitomycin C) and radiation. • Prognosis: 5-year survival rate • Tumors of perianal skin: 80% • Anal canal tumors: • Epidermoid: 50% • Malignant melanoma: 15%

38. Ostomies • What is an ostomy? • It is a man-made fistula in which GI tract is connected to the skin of abdominal wall or to the lumen of another hollow organ. • What is the difference between colostomy and ileostomy?