Colon and Appendix

• Ileo-anal distance


  1.5 meter
• Taenia coli

  • Longitudinal muscle bands that shorten the colon and form haustra
• Ileocaecal valve


  Should be competent, nodular and bilabial types
• Caecum


  • RFI, may be mobile, sometimes totally intraperitoneal, sometimes partially retroperitoneal
• Ascending Colon


  • Extraperitoneal, in the anterior pararenal space
• Hepatic flexure


  • Forms 2 curves: Proximal posterior curve against right kidney and duodenum and a distal anterior curve against the gallbladder
• Transverse colon


  • Intraperitoneal, suspended from the transverse mesocolon
• Splenic flexure


  • Anchored by the phrenocolic ligament, which separates pathology in the left subphrenic space from the left paracolic gutter
• Descending colon


  • Extraperitoneal
• Sigmoid


  • Intraperitoneal and mobile
• Prone versus supine position


  • For viewing the sigmoid colon and rectum
• Filling defects/masses

  • Polyps
  • Tumours
  • Air bubbles
  • Faecal material
  • Mucus
  • Foreign bodies
• Polyps


  Can be pedunculated or sessile - may cause the "bowler hat" sign
• Filling defects

  • Colorectal Ca
  • Polyps and associated syndromes
  • Lymphoid hyperplasia
  • Lymphoma
  • Lyomyomas, lyomyosarcomas
  • Lipomas
  • Extrinsic masses
• Colorectal Adeno Carcinoma


  Most common GIT malignancy, risk factors include ulcerative colitis, Crohn's, familial adenomatous polyposis, and Peutz-Jeghers, 50% originate in the rectum and rectosigmoid, 25% originate in the sigmoid, 25% equally distributed between the remaining colon, most are annular constrictive lesions, 2-6 cm in diameter, with "rolled" borders and ulcerated mucosa, polypoid tumours are less common, scarce is the scirrous type which is analoque to linitis plastica, tumours spread directly to the pericolic fat and surrounding organs, via lymphatics to regional nodes, and hematogenous via the portal system to the liver and systemic circulation, intraperitoneal spread also occurs sometimes, obstruction is the most common complication, scarce complications are perforation, intussusception, abscess formation, and fistula formation, +/- 5% have a simultaneous second carcinoma
• Polyp types


  • Hyperplastic polyps: Round, sessile, <5mm, no risk of malignancy
  • Adenomatous polyps: A premalignant condition, present in 5-10% of people of 40+ years
  • Hamartomatous polyps (juvenile ~): No risk of malignancy, cause rectal bleeding in children, seen in certain syndromes like Peutz-Jeghers and Cowden's disease
  • Inflammatory polyps: Multiple, associated with inflammatory bowel disease
• Polyp risk of malignancy


  Polyps <5mm: 0.5% risk

  Polyps 5-10mm: 1% risk

  Polyps 10-20mm: 10% risk

  Polyps >20mm: 50% risk
• Familial Adenomatous Polyposis

  • Autosomal dominant, patients have multiple polyps which increases with age, develops cancer at 40+ years age, Gardner described a triad of skin, soft tissue and bone lesions (osteomas of skull and mandible), this being a subtype of F.A.P.
• Lymphoid hyperplasia


  May involve the colon, multiple small nodules 1-3mm in trans section
• Lymphoma of the colon


  Less common than lymphoma of the stomach and small bowel, higher incidence with AIDS, small or big nodules that ulcerate, cavitate or perforate, NHL > Hodgkins, otherwise diffuse infiltration with thickened folds and wall thickening
• Lyomyomas and lyomyosarcomas


  Scarce, exofitic, mural or intraluminal, mostly >25mm, ulcerate frequently
• Lipomas


  Common, especially right sided colon, =/- 40% present with intussusception, 1-3cm filling defects, can change its form with compression, measures fat on CT
• Extrinsic masses


  Generally causes an impression on the bowel, endometriosis: sigmoid and rectum involved, metastases: cause wall thickening, increase distance between bowel folds, spiculation (also seen with inflammation), narrowing, angulation and serosal plaques, extrinsic inflammatory processes: appendicitis, pelvic abscesses etc.
• Inflammatory bowel conditions

  • Ulcerative colitis
  • Crohn's
  • Pseudomembranous colitis
  • Amebiasis
  • Ischemic colitis
  • AIDS-related colitis
  • Radiation colitis
  • Cathartic colon
• Ulcerative colitis


  Idiopathic, patients 20-40 years, superficial ulcerations, edema, hyperemia, radiological features: granular mucosa, continuous superficial ulcers, later narrowing of the lumen, progresses throughout the colon from the rectum proximally, confusion can be caused by the deeper "collar button" ulceration, caused by contrast stretching deeper into the submucosal crypts, later: polyp formation - pseudo polyps appears due to residual edematous mucosa between the big areas of continuous ulcera, as well as post inflammatory polyps seen in the remission phase of the disease, "backwash ileitis" is a rare appearance, complications: stricture 2-3 cm in rectum, transverse colon, colorectal Ca- 1% per year risk, toxic megacolon 2-5%, massive bleeding, extra-intestinal features: sacro-ileitis 20%, eye lesions 10%
• Crohn's


  Involves the colon in 2/3 of cases, isolated only to colon in 1/3 of cases
• Types of colitis

  • Radiation colitis
  • Cathartic colon
  • Ulcerative colitis
• Ulcerative colitis


  • Idiopathic, patients 20-40 years
  • Superficial ulcerations, edema, hyperemia
  • Radiological features: Granular mucosa, continuous superficial ulcers, later narrowing of the lumen, progresses throughout the colon from the rectum proximally
  • Confusion can be caused by the deeper "collar button" ulceration, caused by contrast stretching deeper into the submucosal crypts
  • Later: Polyp formation : pseudo polyps appears due to residual edematous mucosa between the big areas of continuous ulcera, as well as post inflammatory polyps seen in the remission phase of the disease
  • "Backwash ileitis" is a rare appearance
  • Complications: Stricture 2-3 cm in rectum, transverse colon, Colorectal Ca- 1% per year risk, Toxic megacolon 2-5%, Massive bleeding
  • Extra-intestinal features: Sacro-ileitis 20%, eye lesions 10%
• Crohn's


  • Involves the colon in 2/3 of cases, isolated only to colon in 1/3 of cases
  • Features: Early aphthous ulcers, later deep confluent ulcers, non-circumferential, non-continuous involvement with normal colon in between; stricture, fistulae and sinuses
  • Pseudodiverticulae: Due to fibrosis of the one side of the colon with saccular projections contralaterally
  • Involves rectum in 50% vs. 100% by ulcerative colitis
  • Involves especially the terminal ileum
  • Low risk for progression to cancer
• Pseudomembranous colitis


  • Bacterial overgrowth and pseudomembrane formation, precipitated by several factors: eg. antibiotics, surgery, radiation etc.
  • Presents with a severe colitis
  • Abdominal films: Dilated colon, nodular haustra, ascites
  • Barium enema: "Thumbprinting", superficial ulcers, plaque-like filling defects
  • CT: Wall thickening : 15mm with "halo/target" appearance, typical stripes of contrast between thickened walls ("accordion sign"), pericolic fat inflammation, ascites
• Amebiasis


  • Trophozoites are set free in the small bowel after ingestion, migrates then to the colon where they bury themselves submucosally and form small abscesses
  • May spread hematogenous or directly
  • Mimics Crohn's radiologically: Aphthous or deep ulcers, asymmetrical with "skip lesions"
  • Complications: Stricture, ameboma formation (a hard granuloma that can look like a Ca ), toxic megacolon, fistulae, liver abscesses and pleural effusions
• Ischaemic Colitis


  • May mimic Crohn's or Ulcerative Colitis clinically/radiologically
  • Follows after vascular insufficiency eg. arteriosclerosis, vasculitis etc. or venous trombosis eg. protrombotic conditions – oral contraception, low flow conditions – heart failure, hypotension etc.
  • The anatomical pattern involved give a clue to the underlying condition
  • S.M.A.: Caecum to splenic flexure
  • I.M.A.: Splenic flexure to rectum
  • Radiological signs : "Thumbprinting", later ulcerations, perforations, scarring, stricture, pneumatosis intestinalis
  • CT: Symmetrical or lobulated bowel wall thickening with irregular narrowed lumen, low density ring of edema submucosally
  • Sometimes even thrombus visible in S.M.A./S.M.V.
• AIDS-related colitis


  • When CD4 -count goes below 200
  • Secondary to CMV, cryptosporidium, HIV itself
  • Right colon disease with ulceration and colitis
• Radiation colitis


  • May be indistinguishable from early ulcerative colitis
  • The result of radiation related endarteritis
  • Radiologically: Thickened walls, ulceration, stricture, spiculation, sometimes fistulae
  • Later fibrosis with a rigid bowel
  • Healing can lead to pseudopolyps and polyps
  • History essential
• Cathartic colon


  • Due to laxatives eg. senna, caster oil
  • Radiologically: Dilated colon, ahaustral
  • Especially right colon
• Types of diverticular disease


  • Diverticulosis: An acquired state where the mucosa and muscularis mucosa herniates through the muscularis propria
  • Diverticulitis: Inflammation of diverticulae, with perforation or pericolic abscess formation, seen in up to 20% of diverticulosis cases
  • Complications of diverticulae includes obstruction, bleeding, peritonitis, sinus tract en fistula formation
• Diverticulosis


  • A painless bleed and diverticulitis can be life threatening
  • Enema shows from small lesions to bigger gas- or contrast filled diverticulae
  • CT also shows muscle hypertrophy as well as a thickened colon wall
• Diverticulitis


  • Inflammation of diverticulae, with perforation or pericolic abscess formation, seen in up to 20% of diverticulosis cases
  • Barium enema is safe EXCEPT if free air or sepsis are present.CT demonstrates the paracolic inflammation and complications better
• Causes of lower GI bleeding


  • Colon diverticulae
  • Angiodisplasia
  • Colon Ca
  • Polyps
• Angiodisplasia


  Refers to age related unfolding of submucosal veins, with acute or chronic lower G.I.T. bleeding