Case Discussion,Tang Chun Xiang 2016/5/25,Axial arterial phase,Axial arterial phase,Axial venous phase,Coronal arterial phase,Sagittal venous phase,Crohn disease,An inflammatory disease of the gastrointestinal tract that typically has an indolent course Characterized by intestinal ulceration, strictures, and fistula formation Commonly affects young adults, small bowel, particularly the terminal ileum Small bowel involvement in Crohn disease is typically transmural, with skip lesions CT and MRI,Introduction-Crohn disease,CT and MRI Useful for differentiating between active and fibrotic bowel strictures Allowing visualization of the entire thickness of the bowel wall Depicting extraenteric involvement Providing more detailed and comprehensive information about the extent and severity,Introduction-Crohn disease,Comb sign Fat halo sign Bowel wall enhancement Bowel wall thickness Stricture and fistula Mesenteric/intra-abdominal abscess (15%-20%) or phlegmon formation Ulcerations and loss of haustration Creeping fat,Imaging findings on CT and MRI,Comb sign Prominence of the vasa recta adjacent to the inflamed loop of bowel Transmural extension of inflammation across the serosa and to engorgement of the hyperemic vasa recta surrounding the inflamed bowel segment Not pathognomic of Crohn disease,Imaging findings on CT and MRI,Fat halo sign Infiltration of the submucosa with fat, between the muscularis and the mucosa Confused with the fat ring sign of mesenteric panniculitis Nearly pathognomonic of inflammatory bowel disease (Crohn disease and ulcerative colitis),Imaging findings on CT and MRI,Bowel wall enhancement The result of increased vascular permeability and angiogenesis The most sensitive indicator of active Crohn disease Enhancement can be graded by comparing to the precontrast images Minor increased enhancement Moderate enhancement Marked enhancement No abnormal enhancement: equivalent to normal bowel wall,Imaging findings on CT and MRI,Pattern of enhancement,Bowel wall thickness Normal bowel wall thickness： lumen distended， 1-2 mm； lumen collapsed, 3-4 mm Mild: 3-5 mm Moderate: 5-7 mm Marked: 7mm One of the most common signs, but not specific Correlates well with the severity of the disease activity Measure when lumen distended well Black border artifacts can distort thickness measurements,Imaging findings on CT and MRI,Stricture A complication of Crohn disease Reversible strictures produced by active disease A lack of enhancement and loss of stratification might be seen in the presence of transmural fibrosis,Imaging findings on CT and MRI,Fistula The detection of penetrating disease is important and may redirect or alter management Enteroenteric fistula, enterovesical fistula, and interloop abscess CT enterography resulted in accurate detection of fistulas in 94% of cases,Imaging findings on CT and MRI,Abscess Often seen in patients with severe active Crohn disease Extraluminal fluid collections without communication with the bowel lumen Fluid collections with an enhancing wall with or without associated air,Imaging findings on CT and MRI,Ulceration Moderate to deep ulceration can be seen, small ulcerations can be difficult to distinguish Active spots of inflammation Increased enhancement,Imaging findings on CT and MRI,Loss of haustration Both the colon and the small bowel are involved in 30%60% Involvement of the colon alone in 20%35% A decrease of haustral folds A common finding in ulcerative colitis,Imaging findings on CT and MRI,Creeping fat Fibrofatty proliferation of fat wrapping, different name for hypertrophy of the subserosal fat Common finding in longstanding Crohn disease The image shows creeping fat surrounding bowel loops,Imaging findings on CT and MRI,CT and MRI Useful for differentiating between active and fibrotic bowel strictures,Summary,CT features of active Crohn disease Mucosal hyperenhancement Wall thickening (thickness 3 mm) Mural stratification with a prominent vasa recta (comb sign),CT features of inactive longstanding Crohn disease Submucosal fat deposition (fat halo sign) Surrounding fibrofatty proliferation (creeping fat), and fibrotic strictures Pseudosacculation,CT and MRI Allowing visualization of the entire thickness of the bowel wall,Summary,Normal bowel wall thickness： lumen distended， 1-2 mm； lumen collapsed, 3-4 mm Mild: 3-5 mm Moderate: 5-7 mm Marked: 7mm,CT and MRI Depicting extraenteric involvement,Summary,Fistula and abscess Enteroenteric fistula Enterovesical fistula Interloop abscess Etc.,CT and MRI Providing more detailed and comprehensive