Imaging of the large bowel

large Bowel

1. IMAGING OF THE LARGE BOWEL Dr.Archana Koshy 2/29/2016 IMAGING OF LARGE BOWEL 1

2. OVERVIEW Anatomy Investigations Large bowel obstruction . Colorectal tumours Diverticular disease Colitis Miscellaneous conditions Rectum and presacral space Anus 2/29/2016 IMAGING OF LARGE BOWEL 2

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6. The colon is necessary for optimal absorption of nutrients , water and electrolytes and transit and storage of residue . Colonic innervation is extremely complex . Input from the Autonomic nervous system , extra intestinal autonomic ganglia and the enteric nervous system Certain sites are prone to physiological narrowing – Ileocaecal valve . 2/29/2016 IMAGING OF LARGE BOWEL 6

7. RADIOLOGICAL INVESTIGATIONS PLAIN FILMS : (ERECT/SUPINE) Intraluminal Colonic gas is normal Close temporal proximity to either sigmoidoscopy or colonoscopy may cause excessive colonic gas – should not be mistaken for a pathology . 2/29/2016 IMAGING OF LARGE BOWEL 7

8. BARIUM ENEMA Gold standard technique for imaging fine mucosal detail . Scrupulous colon cleansing is mandatory for high quality studies . Barium suspensions are contra indicated if there is a risk of colonic perforation . A series of films are taken to image the entire colon in double contrast . 2/29/2016 IMAGING OF LARGE BOWEL 8

9. EVACUATION PROCTOGRAPHY (DEFECOGRAPHY) Images rectal configuration during evacuation of a barium paste The subject is seated upright on a specifically designed radio opaque commode. Used to investigate difficult rectal evacuation . May be modified by the addition of bladder , vaginal and small bowel contrast – the entire pelvic floor . 2/29/2016 IMAGING OF LARGE BOWEL 9

10. COLONIC TRANSIT STUDIES Used to investigate severely constipated patients Measurement of whole gut transit time using radio opaque markers , Ingested and followed by an abdominal film after an appropriate interval . RECTAL ULTRASOUND Uses a 360⁰ rotating endoprobe Obtains high resolution axial images of the rectal wall Primarily used to stage tumours . ANAL ENDOSONOGRAPHY Modified rectal endoprobe to image the anal sphincters in patients who are anally incontinent . 2/29/2016 IMAGING OF LARGE BOWEL 10

11. LARGE BOWEL OBSTRUCTION Acute abdominal emergency with high morbidity and mortality rates if left untreated . A bdominal radiography is usually the initial imaging study performed . Computed tomography is the imaging method of choice as it can establish the diagnosis and cause of large-bowel obstruction . A contrast agent enema may be used to confirm or exclude large-bowel obstruction . The marked distension of colon proximal to the level of obstruction leads to M ucosal edema B owel ischemia If not treated, bowel infarction and perforation. 2/29/2016 IMAGING OF LARGE BOWEL 11

12. Patients with LBO are usually elderly . signs and symptoms are often insidious in contrast to the abrupt onset of symptoms seen in most SBOs A bdominal pain, constipation or obstipation and abdominal distension . The major sites of obstruction include the cecum, hepatic and splenic flexures and recto-sigmoid colon . O ccurs more frequently within the left colon . 2/29/2016 IMAGING OF LARGE BOWEL 12

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14. 2/29/2016 IMAGING OF LARGE BOWEL 14 X-ray abdomen, supine view shows a HUGELY DILATED LOOP arising from the pelvis with the “ COFFEE-BEAN” SIGN in a case of SIGMOID VOLVULUS

15. 2/29/2016 IMAGING OF LARGE BOWEL 15 64-YEAR-OLD MAN WITH LBO CAUSED BY A COLOCOLONIC INTUSSUSCEPTION. CT scout image shows air-filled dilated colon terminating abruptly in the left upper quadrant . (b) Coronal reformatted CT image of the abdomen and pelvis shows a transverse colonic intussusception.

16. 2/29/2016 IMAGING OF LARGE BOWEL 16 Transverse CT image of the pelvis in an 85-year-old woman with LBO caused by distal fecal impaction . I CT CONTRAST displayed using Lung window shows a dilated colon and large mass of impacted stool in the rectum (arrow )..

17. COLORECTAL TUMOURS POLYPS M acroscopic circumscribed tumour or mucosal elevation that projects above a surrounding flat epithelial surface . Polyps smaller than 5 mm diameter are most often inflammatory or metaplastic lesions that have no malignant potential. Medium (6–9 mm) and large (10 mm and more) polypoid lesions are frequently neoplastic polyps, most often adenomas . Other non-neoplastic polyps that occur in the colon are hamartomatous polyps- found in the Peutz – Jeghers syndrome Juvenile polyps may be single or multiple, and may be found in children and adults . 2/29/2016 IMAGING OF LARGE BOWEL 17

18. Adenomatous polyps are common with the prevalence of 5–10% in asymptomatic individuals older than 40 years of age. A term “ADVANCED ADENOMA” has been introduced to emphasise the significance of polyps >10 mm diameter, whereas small polyps (<10 mm) are frequently considered inconsequential. Adenomatous polyps are SHARPLY CIRCUMSCRIBED, SESSILE OR PEDUNCULATED LESIONS that tend to arise more frequently in the rectosigmoid region , with a similar distribution of carcinomas 2/29/2016 IMAGING OF LARGE BOWEL 18

19. Radiological signs of a polyp on double contrast enema MENISCUS SIGN - A meniscus of barium forms around the base of the polyp. When viewed en face, there is a ring shadow with a sharp inner ring due to the soft tissue-barium interface and a fuzzy outer ring due to fading of the barium peripherally . (2) When it lies within a pool of barium, it appears as a negative filling defect . (3) When viewed obliquely, there is a thin meniscus of barium over its surface creating “the bowler hat sign ". (4) If the polyp is pedunculated , a stalk is visible with a parallel tram track of barium. 2/29/2016 IMAGING OF LARGE BOWEL 19

20. 2/29/2016 IMAGING OF LARGE BOWEL 20 Small polyp where the meniscal rim of barium between the polyp base and adjacent mucosa causes the 'bowler-hat' sign.

21. 2/29/2016 IMAGING OF LARGE BOWEL 21 WHEN SEEN EN FACE, STALKED POLYPS PRODUCE A 'TARGET' SIGN.

22. CT COLONOGRAPHY F acilitates a rapid complete interrogation of the colon and rectum . T he attenuation characteristics of any suspicious lesion helps differentiate faecal residue from polyp, as variable attenuation due to some gas content is a distinguishing feature of residue , but a polyp has uniform attenuation similar to the bowel wall F aecal residue tends to fall onto the dependent colon surface, whereas polyps maintain their position despite patient movement . A definitive diagnosis of a lipoma is based on its fat density . 2/29/2016 IMAGING OF LARGE BOWEL 22

23. 2/29/2016 IMAGING OF LARGE BOWEL 23 CT COLONOGRAPHY OF A LARGE SIGMOID POLYP WITH HOMOGENEOUS ATTENUATION

24. 2/29/2016 IMAGING OF LARGE BOWEL 24 2D CT colonography of a polypoid lesion in the caecum . On standard abdominal windowing the attenuation of this polyp is the same as for fat, confirming a lipoma

25. 2/29/2016 IMAGING OF LARGE BOWEL 25 Magnified view of the sigmoid colon demonstrates THE MID-SIGMOID SESSILE POLYP EN FACE .

26. 2/29/2016 IMAGING OF LARGE BOWEL 26 SESSILE PEDUNCULATED Pedunculated

27. ADENOMAS : Benign neoplasms of colorectal epithelium . Dysplastic and potentially pre malignant with increased incidence with age . Villosity and dysplasia –Most important predictors of malignancy. May be (a) Tubular (b) Tubulovillous (c) Villous Villous adenomas have characteristic morphology , being broad and relatively large ,with a frond like surface . Most adenomas are asymptomatic but large polyps may bleed or causes electrolyte disturbance secondary to mucus secretion . Malignancy is defined by Invasive adenocarcinoma – Cells penetrate the muscularis mucosa to reach the submucosa . MALIGNANT POLYP – When a focus of invasive carcinoma is found within an excised adenoma . 2/29/2016 IMAGING OF LARGE BOWEL 27

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30. POLYPOSIS SYNDROMES Seemingly innocuous polyps that carry no risk of malignancy when single can convey increased risk when multiple. PEUTZ JEGHERS SYNDROME : Autosomal dominant condition characterised by mucocutaneous pigmentation and intenstinal hamartomatous polyps . Patients may suffer from repeated episodes of intussusception . The hamartomas have no intrinsic malignant potential, but the overlying mucosa may become dysplastic- increased risk of upper GI cancer. Increased risk of extra-intestinal cancers, particularly of the ovary, thyroid, testis, pancreas and breast. 2/29/2016 IMAGING OF LARGE BOWEL 30

31. 2/29/2016 IMAGING OF LARGE BOWEL 31 PEUTZ JEGHERS SYNDROME - A LARGE PEDUNCULATED POLYP AND A SMALLER SESSILE POLYP PROXIMALLY .

32. JUVENILE POLYPOSIS V ery rare and presents in infancy. The polyps are hamartomatous with cystic epithelial tubules in an excess of lamina propria – the ‘Swiss cheese’ effect. T ypically smooth and pedunculated . 50–200 polyps in the colon, with further lesions in the small bowel and stomach. Epithelial dysplasia is common in young adults, either in the juvenile polyps or in coexisting adenomas . S ignificant risk of colorectal cancer in this condition. 2/29/2016 IMAGING OF LARGE BOWEL 32

33. HEREDITARY NON-POLYPOSIS COLORECTAL CANCER caused by a fault in the DNA mismatch repair gene and probably accounts for 5 per cent of all colorectal cancer. The criteria for this condition include (A) three or more relatives with CRC (B) one of these is a first-degree relative (C ) cases over two or more generations (D ) CRC diagnosed before the age of 50 years . Cancers occur at an earlier age in HNPCC. 70 per cent are in the proximal colon and multiple tumours are common . 2/29/2016 IMAGING OF LARGE BOWEL 33

34. 2/29/2016 IMAGING OF LARGE BOWEL 34 SMALL RING SIGN EN FACE DUE TO A 3 MM POLYP IN THE DESCENDING COLON OF A 32-YEAR-OLD WOMAN WITH HNPCC

35. FAMILIAL ADENOMATOUS POLYPOSIS M utation of the APC tumour suppression gene on chromosome 5q21 and accounts for about 1 per cent of CRC . Classically micro-adenomas develop in the early teens, becoming macro-adenomas in the late teens. M ore than 100 adenomas have to be present for the diagnosis, and typically several hundred polyps are present throughout the large bowel. R ectal bleeding, diarrhoea and m ucus discharge . Two-thirds of symptomatic patients already have an overt cancer . A ll affected patients eventually develop large-bowel carcinoma, so that restorative proctocolectomy is now recommended once the condition has been diagnosed. 2/29/2016 IMAGING OF LARGE BOWEL 35

36. 2/29/2016 IMAGING OF LARGE BOWEL 36 Double Contrast Barium enema view of the descending colon Multiple small polyps about 5 mm in size creating ring shadow menisci around their bases , or as a filling defect in the barium pool

37. 2/29/2016 IMAGING OF LARGE BOWEL 37 Innumerable colonic adenomas .

38. COLORECTAL CANCER Believed to arise from pre existing adenomatous polyps Colorectal cancer incidence increases with age but mortality rates have fallen over the years, probably due to poylpectomy Risk of developing colorectal cancer is closely related to family history . Change in bowel habit , rectal bleeding and abdominal pain . The majority of colorectal cancers are believed to arise from sporadic adenomas ( adenoma-carcinoma sequence ) Adenomas are defined by dysplasia and cancer occurs when the invasive adenocarcinoma crosses the muscularis mucosa to reach the submucosa . 2/29/2016 IMAGING OF LARGE BOWEL 38

39. Surgical excision is relatively straightforward in the colon unless the tumour is infiltrating locally . The Dukes' and TNM systems both describe the extent of tumour growth and nodal involvement. Involvement of the mesorectal fascia is particularly important when planning total mesorectal excision, as fascial compromise necessitates pre-operative radiotherapy to prevent local recurrence. 2/29/2016 IMAGING OF LARGE BOWEL 39

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42. 2/29/2016 IMAGING OF LARGE BOWEL 42 A POLYPOID CARCINOMA WITH AN IRREGULAR INDRAWN BASE

43. 2/29/2016 IMAGING OF LARGE BOWEL 43 A plaque-like carcinoma at the hepatic flexure that has a smooth surface and is recognized in this view only by its raised edge creating a defect in the barium pool

44. CT COLONOGRAPHY Shows the extent of wall thickening ( normal distended colonic wall <4 mm ) and extramural infiltration. With standard abdominal CT, the enhancement within a tumour is usually homogeneous, but may be heterogeneous with large adenocarcinomas or mucinous tumours . Extramural spread is suggested by the presence of irregular projections from the serosal surface into the surrounding fat, with clouding of the pericolic fat and thickening of contiguous fascial reflections. 2/29/2016 IMAGING OF LARGE BOWEL 44

45. Loss of normal fat planes is suggestive of local invasion. Enhancement differentiates nodes from vessels. Nodal enlargement may be due to reactive hyperplasia or metastatic involvement. The presence of retroperitoneal nodes or pelvic nodes >1.0 cm in diameter, or clusters of more than three intra-abdominal nodes, suggests metastatic involvement. Ascites, peritoneal deposits and omental caking indicate diffuse intra-peritoneal spread. 2/29/2016 IMAGING OF LARGE BOWEL 45

46. Frank carcinoma appears as an annular , irregular , ulcerated lesion – APPLE CORE APPEARANCE Abrupt , shouldered margins Normal mucosal folds cannot be traced through the stricture indicating mucosal destruction 2/29/2016 IMAGING OF LARGE BOWEL 46

47. 2/29/2016 IMAGING OF LARGE BOWEL 47 Annular carcinoma revealing the irregular lumen and thickened bowel wall

48. 2/29/2016 IMAGING OF LARGE BOWEL 48 64-year-old woman with locally advanced colon cancer presenting as palpable mass in right upper quadrant . A- Transverse ultrasound image shows colonic wall thickening . B- Contrast-enhanced CT image confirms transverse colon mass with greater nodularity along anterior mural surface and abdominal wall invasion.

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51. SECONDARY CANCER 2/29/2016 IMAGING OF LARGE BOWEL 51 Dissemination - direct invasion , along mesenteric planes, lymphatic permeation, intraperitoneal seeding or by haematogenous spread . Gastric cancer may invade the colon via the gastrocolic ligament, and pancreatic cancer via the transverse mesocolon . Ascitic flow causes tumour implantation mainly in the pelvis, loops of small bowel in the right iliac fossa, superior border of the colon and right paracolic gutter . Peritoneal spread also involves the omentum , and omental cakes of tumour typically involve the root of the omentum at its attachment to the transverse colon. This is another cause of extrinsic masses involving the transverse colon. The metastases may be multiple, polypoid with a smooth surface due to their submucosal location, and are often umbilicated as a result of differential growth between the centre and the periphery.

52. 2/29/2016 IMAGING OF LARGE BOWEL 52 MULTIPLE BIZARRE STRICTURES AND MUCOSAL PLEATING IN A WOMAN WITH EXTENSIVE PERITONEAL CARCINOMATOSIS FROM AN OVARIAN PRIMARY

53. 2/29/2016 IMAGING OF LARGE BOWEL 53 ENLARGED LYMPH NODES IN A 43-YEAR-OLD MAN WITH METASTATIC COLON CANCER . MULTIPLE HEPATIC METASTASES AS WELL AS ENLARGED PORTACAVAL AND AORTOCAVAL NODES .

54. 2/29/2016 IMAGING OF LARGE BOWEL 54 PULMONARY METASTASES IN A 47-YEAR-OLD MAN WITH COLON CANCER . SPIRAL CT SCAN SHOWS NUMEROUS METASTASES IN THE LUNGS .

55. DIVERTICULITIS Diverticulosis – acquired pulsion diverticula due to the increased colonic segmental pressure . -Mucosal herniations through vasular entry sites into pericolic fat . Diverticulitis – Super imposed inflammation Diverticular disease – Encompasses both concepts . 2/29/2016 IMAGING OF LARGE BOWEL 55

56. The sigmoid colon is typically affected . Muscular thickening due to elastosis ---Luminal narrowing Causes progressive elastosis ----Longitudinal foreshortening and accentuation of sigmoid corrugations . Due to micro/ macroperforation pericolic fibrosis and inflammation also contribute . Muscles covering the diverticula tend to atrophy as they enlarge so that mucous membrane , connective tissue and peritoneal tissue cover the mature diverticula . 2/29/2016 IMAGING OF LARGE BOWEL 56

57. The diverticula appear as flask or rounded like out pouchings . The produce ring shadows . Projection beyond the bowel wall and the presence of a fluid level within it- differentiates it from a polyp Muscular change results in a serrated like appearance Pronounced and persistent spasm, which reflects abnormal motility . 2/29/2016 IMAGING OF LARGE BOWEL 57

58. 2/29/2016 IMAGING OF LARGE BOWEL 58 BARIUM ENEMA- SEVERE SIGMOID DIVERTICULAR DISEASE WITH A COMPLICATING FISTULA TO THE VAGINA

59. 2/29/2016 IMAGING OF LARGE BOWEL 59 FOCAL, MASSLIKE THICKENING OF THE SIGMOID COLON (STRAIGHT ARROWS) WITH ADJACENT STRANDING OF THE PERICOLIC FAT MINIMAL ADJACENT MESENTERIC FLUID (CURVED ARROW) FAVORED DIVERTICULITIS.

60. 2/29/2016 IMAGING OF LARGE BOWEL 60 WALL THICKENING IN THE SIGMOID COLON (ARROWS) WITH ADJACENT INFLAMMATORY CHANGES IN THE PERICOLIC FAT.

61. COMPLICATIONS Diverticulitis results in pericolic abcess and localised peritonitis . Obstruction may complicate an episode of diverticulitis and spasm may be severe enough to obiliterate the lumen. Extension of the inflammation to a neighbouring viscera may lead to FISTULATION Symptoms – Pneumaturia and recurrent UTI . Diverticular disease – cause of torrential and life threatening haemorrhage in the elderly Accounts for majority of Lower GI bleeds in this age group . 2/29/2016 IMAGING OF LARGE BOWEL 61

62. 2/29/2016 IMAGING OF LARGE BOWEL 62 FOCAL WALL THICKENING IS SEEN IN THE LEFT POSTERIOR PART OF THE BLADDER ADJACENT TO THE INFLAMED SIGMOID (ARROW ). A MODERATE AMOUNT OF AIR IS ALSO PRESENT IN THE BLADDER, A FINDING COMPATIBLE WITH A COLOVESICAL FISTULA.

63. 2/29/2016 IMAGING OF LARGE BOWEL 63 CT WAS USED TO PLACE A PERCUTANEOUS DRAIN INTO THIS LARGE PARACOLIC COLLECTION SECONDARY TO DIVERTICULAR DISEASE .

64. COLITIS Describes colonic inflammation broadly divided into : IDIOPATHIC ULCERATIVE COLITIS CROHN’S DISEASE 2. ISCHEMIC 3. INFECTIOUS HALLMARK –Mucosal inflammation and ulceration Contrast enemas remain the corner stone for the diagnosis . 2/29/2016 IMAGING OF LARGE BOWEL 64

65. ULCERATIVE COLITIS Characterised by relapsing and remitting proctitis Rectum is always affected . Affects young adults (15-25 ) years . Attacks are characterised by bloody diarrhea EXTRA INTESTINAL MANIFESTATIONS – -Arthralgia -Erythema Nodosum - Pyoderma Gangrenosum - Sclerosing Cholangitis 6. Proctoscopy and sigmoidoscopy with biopsy are essential . 7 . The changes progress through mucosal granularity and spontaneous haemorrhage to frank, continuous ulceration . 2/29/2016 IMAGING OF LARGE BOWEL 65

66. PLAIN FILMS In total colitis , the reliable features on air enema- -Irregularity of the mucosal edge -Increased thickness of the colon wall . In the absence of enough spontaneous intraluminal air to assess the colonic wall, AIR ENEMA may be done . Plain films are used to detect ACUTE TOXIC MEGACOLON/DILATATION ( when transverse colonic diameter >5.5 cm ) The transverse colon is the most dilated on plain films , due to the patients supine position . The mucosal line is irregular producing MUCOSAL ISLANDS. The colon has a consistency akin to blotting paper, so patients are at risk of perforation and untimely death . 2/29/2016 IMAGING OF LARGE BOWEL 66

67. 2/29/2016 IMAGING OF LARGE BOWEL 67 TOXIC MEGACOLON – LUMINAL DILATATION , ABNORMAL HAUSTRATION WITH MURAL THICKENING .

68. Proctosigmoidoscopy is 10-15% more sensitive overall for primary diagnosis of early , distal ulcerative colitis . Contrast enema – Can accurately demonstrate colonic morphology -Exact location and extent of any stricture can be identified . Any Barium examination is acutely contraindicated If there is evidence of toxic dilatation . 2/29/2016 IMAGING OF LARGE BOWEL 68

69. RADIOLOGICAL FEATURES Earliest change - Blurring of the mucosal line and a fine granularity when mucosa is seen en face Abnormal barium adherence to altered colonic mucous Flecks of barium adhering to superficial erosion . As the disease progresses, the granularity becomes coarser and eventually frank ulceration develops – Projections of barium outside the mucosal line . Ulceration is continuous and tends to be superficial Mucosal changes are accompanied by haustral blunting , luminal narrowing and colonic shortening . A tubular , short , featureless colon is typical of long standing colitis . 2/29/2016 IMAGING OF LARGE BOWEL 69

70. 2/29/2016 IMAGING OF LARGE BOWEL 70 . CT scan of a patient with long-standing ulcerative colitis A SUBMUCOSAL HALO OF FAT WITHIN THE RECTUM (ARROW ) PERIRECTAL FIBROFATTY PROLIFERATION (*).

71. 2/29/2016 IMAGING OF LARGE BOWEL 71 Transverse CT image in a 32-yearold woman with ulcerative colitis and bloody diarrhea demonstrates the double halo, or target, sign with inner (mucosa, arrow) and outer ( muscularis propria , arrowhead) rings of high attenuation separated by a ring of low attenuation, which represents submucosa with edema.

72. 2/29/2016 IMAGING OF LARGE BOWEL 72 TRANSVERSE CT IMAGE IN A 35-YEAROLD PATIENT WITH ULCERATIVE COLITIS AND TOXIC MEGACOLON SHOWS MARKEDLY DISTENDED TRANSVERSE COLON WITH SHAGGY MUCOSA (ARROWS).

73. CROHN’S DISEASE Chronic relapsing immune mediated inflammatory disease, with transmural and segmental involvement of the small bowel. Mouth to anus often with multiple skip discontinuous areas. The most common site is the small bowel (80%), the terminal ileum being most commonly affected site in the small bowel. Approximately ¼ th will have disease limited to the large bowel and DD from U. Colitis becomes relevant . Abdominal pain, diarrhoea , weight loss- frequent Anemia, acute obstruction,

74. First radiological changes are granularity and aphthous ulceration . APHTHOUS ULCERS – Small and discrete , surrounded by slightly elevated edematous mucosa . -Barium collects in the central depression with the surrounding elevation appearing as a radiolucent halo -occur on a background of normal mucosa . -NEVER SEEN IN ULCERATIVE COLITIS . 2/29/2016 IMAGING OF LARGE BOWEL 74

75. As the disease progresses,ulcers become longitudinal and deeper – TRANSMURAL ulceration . Deep longitudinal ulcers combined with mucosal edema – COBBLESTONE APPEARANCE . Discontinuous , both longitudinally and circumferentially 2/29/2016 IMAGING OF LARGE BOWEL 75

76. 2/29/2016 IMAGING OF LARGE BOWEL 76 CONTRACTION AT THE SITE OF ULCER FORMATION – PSEUDODIVERTICULA

77. 2/29/2016 IMAGING OF LARGE BOWEL 77 US IMAGE OF THE TERMINAL ILEUM-THICKENED (ARROW) WITH THICK, ECHOGENIC SUBMUCOSA RELATED TO LYMPHEDEMA

78. ISCHEMIC COLITIS The colon is particularly vulnerable to mesenteric ischemia . Oedema , haemorrhage and ulceration . S pontaneous healing followed by fibrosis – results in subsequent colonic stricturing , Plain films – Splenic flexure irregularity with mural thickening , Characteristic edematous THUMB PRINTING . 2/29/2016 IMAGING OF LARGE BOWEL 78 SPLENIC FLEXURE “THUMB PRINTING “

79. 2/29/2016 IMAGING OF LARGE BOWEL 79 DIFFUSE ISCHEMIC COLITIS. Diffuse , low-attenuation thickening of the colonic wall (arrows ). This is an example of the halo sign. SEGMENTAL ISCHEMIC COLITIS . F ocal thickening of two colonic loops in the left abdomen (arrows).

80. INFECTIOUS COLITIS Bacterial colitis is common and imaging usually reveals non specific pancolitis . Eg’s : Campylobacter , Salmonella , Shigella , Yersinia TUBERCULOSIS – morphology is similar to crohn’s disease. -A conical , contracted caecum is characteristic ; Longitudinal and aphthoid ulcers may occur . 4. NEUTROPENIC COLITIS (TYPHILITIS)- Occurs in immunocompromised patients , secondary to chemotherapy and presents with right sided inflammation . 5 . GRAFT VERSUS HOST DISEASE – Non specific colitis 2/29/2016 IMAGING OF LARGE BOWEL 80

81. 2/29/2016 IMAGING OF LARGE BOWEL 81 MODERATE THICKENING OF THE COLON (ARROWS) AND INFLAMMATORY CHANGES IN THE MESENTERIC FAT. E COLI WAS CULTURED FROM STOOL

82. 2/29/2016 IMAGING OF LARGE BOWEL 82 52-year-old woman with infectious colitis . Gray-scale ultrasound image shows concentric wall thickening and blurring of normal mural stratification in colon . Power Doppler image reveals marked hyperemia in affected segment .

83. PSEUDOMEMBRANOUS COLITIS 2/29/2016 IMAGING OF LARGE BOWEL 83 Marked colonic wall thickening and mucosal plaques P resents with diffuse watery diarrhea and abdominal cramps. The rectosigmoid colon is almost invariably involved, with 3–8-mm in diameter, creamy, white, elevated plaques or nodules. T he disease can progress to toxic megacolon with transmural injury ..

84. Severe cases show a markedly thickened colonic wall with a “ thumbprinting ,” low attenuation from mucosal and submucosal edema,irregular mucosal contour with polypoid protrusions, pericolonic stranding, and ascites The colonic diameter is often enlarged . After administration of intravenous contrast material, the target sign may be seen with enhanced mucosa and serosa . The average wall thickness is 14.7 mm. 2/29/2016 IMAGING OF LARGE BOWEL 84

85. Marked wall thickening throughout the colon (thickness , 15 mm) and pericolic inflammation. The thickening in the transverse colon is asymmetric 2/29/2016 IMAGING OF LARGE BOWEL 85

86. 2/29/2016 IMAGING OF LARGE BOWEL 86 . IN THE SIGMOID COLON, A SHAGGY THICKENED BOWEL WALL WITH ALTERNATING AREAS OF NECROSIS AND PLAQUES.

87. THE RECTUM The rectum is the last segment of the gastrointestinal tract and is bounded by the sigmoid colon the anus. The proximal portion located within the peritoneal cavity and the distal portion being extraperitoneal . The inferior aspect of the rectum, or the anorectal junction, is defined anatomically by the dentate line, which spans 5–10 mm of the anal canal and marks the transitional zone. 2/29/2016 IMAGING OF LARGE BOWEL 87

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90. RECTAL CANCER 40 % of colorectal cancers occur in the rectum Immobility permits accurate radiotherapy and accessibility allows transanal local excision. Rectal staging is particularly useful . MRI and TRUS remain a higher modality for investigation in comparison to CT- Able to visualise the muscularis propria . 2/29/2016 IMAGING OF LARGE BOWEL 90

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93. 2/29/2016 IMAGING OF LARGE BOWEL 93 A n irregular mass in the rectum with an associated enlarged perirectal lymph node . Axial 2D image obtained at the level of the mid abdomen reveals lymphadenopathy (arrows) along the course of the IMV (arrowhead).

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