 Introduction/Background Crohn disease (CD) is a chronic inflammatory disorder involving the gastrointestinal tract, typically characterized by episodic flares and times of remission. Over the past several decades, there has been an increasing incidence of this disease [1-3]. Any portion of the gastrointestinal tract or alimentary tract may be involved, but the small bowel alone is affected in about a third of patients, the colon alone in a somewhat higher percentage of patients, and combined involvement of the colon and the small bowel is seen in less than a third of patients [4,5]. Perianal disease is another not uncommon manifestation [6]. Pathologically, CD is characterized by transmural granulomatous inflammation [7]. Although the bowel may return to normal after an acute flare, underlying structural damage progressively occurs over time with recurrent bouts of inflammation, leading to stricture formation, penetrating sinuses or fistulas, or a combination of the two [8]. The diagnosis of CD is based on a combination of clinical, laboratory, endoscopic, histological, and imaging findings [7,9]. No single diagnostic test allows unequivocal diagnosis. The imaging characteristics and distribution of disease provide supportive evidence for the diagnosis of CD. In addition, imaging is complementary to endoscopic techniques such as ileocolonoscopy, which allows diagnosis of disease when endoscopy is negative because of intramural disease without associated mucosal activity or because of a lack of colonic and distal ileal involvement [10]. Disease activity has been traditionally determined by clinical factors including patient symptoms and laboratory tests in which indices, such as Crohns Disease Activity Index, help to determine management. There is growing evidence, however, that active inflammation can exist despite clinical resolution of symptoms [11-13] and that complete mucosal healing represents a better treatment target for long-term outcomes than reliance on clinical symptoms [13].
Crohn Disease.  Introduction/Background Crohn disease (CD) is a chronic inflammatory disorder involving the gastrointestinal tract, typically characterized by episodic flares and times of remission. Over the past several decades, there has been an increasing incidence of this disease [1-3]. Any portion of the gastrointestinal tract or alimentary tract may be involved, but the small bowel alone is affected in about a third of patients, the colon alone in a somewhat higher percentage of patients, and combined involvement of the colon and the small bowel is seen in less than a third of patients [4,5]. Perianal disease is another not uncommon manifestation [6]. Pathologically, CD is characterized by transmural granulomatous inflammation [7]. Although the bowel may return to normal after an acute flare, underlying structural damage progressively occurs over time with recurrent bouts of inflammation, leading to stricture formation, penetrating sinuses or fistulas, or a combination of the two [8]. The diagnosis of CD is based on a combination of clinical, laboratory, endoscopic, histological, and imaging findings [7,9]. No single diagnostic test allows unequivocal diagnosis. The imaging characteristics and distribution of disease provide supportive evidence for the diagnosis of CD. In addition, imaging is complementary to endoscopic techniques such as ileocolonoscopy, which allows diagnosis of disease when endoscopy is negative because of intramural disease without associated mucosal activity or because of a lack of colonic and distal ileal involvement [10]. Disease activity has been traditionally determined by clinical factors including patient symptoms and laboratory tests in which indices, such as Crohns Disease Activity Index, help to determine management. There is growing evidence, however, that active inflammation can exist despite clinical resolution of symptoms [11-13] and that complete mucosal healing represents a better treatment target for long-term outcomes than reliance on clinical symptoms [13].