In this clinical variant, there is an established diagnosis of CD. Here, the patient presents with acute worsening of symptoms attributable to known disease. The concern is for an active flare or for the development of a complication of CD (ie, obstruction, abscess, fistula development). The clinical suspicion of an alternative diagnosis mimicking CD is low. CT Abdomen and Pelvis Standard abdomen and pelvis CT with IV contrast with a routine protocol (ie, without oral contrast enterography technique) can be useful in the suspected exacerbation of CD. Although the imaging findings of an acute flare in a known CD patient are typically not subtle (ie, not the situation of subtle mucosal enhancement in a clinically asymptomatic patient undergoing treatment monitoring), optimizing the bowel by enterography technique leads to improved detection of inflammation and should be pursued if the patient can tolerate the oral contrast. On the other hand, CT with positive luminal contrast (without enterography technique) can identify wall thickening, luminal narrowing, and adjacent inflammatory changes that may be seen in CD [19]. In addition, the complications of abscess formation or fistula formation can be detected at standard IV contrast CT in which the positive oral contrast may improve detection of complications. Sensitivities for abscesses are very good, ranging from 86% to 100% [27,36]. There is more variable performance for fistula detection with sensitivities ranging from 68% to 100% [27,40,42]. One study showed a very low sensitivity of 20% for enteroenteric fistulas in their series [40]. Although standard abdomen and pelvis CT can be done either with or without the administration of IV contrast, it is evident that many of the processes seen with an acute flare in CD require IV contrast for optimal assessment. Without IV contrast, such processes can only be inferred by associated findings, such as wall thickening.
Crohn Disease. In this clinical variant, there is an established diagnosis of CD. Here, the patient presents with acute worsening of symptoms attributable to known disease. The concern is for an active flare or for the development of a complication of CD (ie, obstruction, abscess, fistula development). The clinical suspicion of an alternative diagnosis mimicking CD is low. CT Abdomen and Pelvis Standard abdomen and pelvis CT with IV contrast with a routine protocol (ie, without oral contrast enterography technique) can be useful in the suspected exacerbation of CD. Although the imaging findings of an acute flare in a known CD patient are typically not subtle (ie, not the situation of subtle mucosal enhancement in a clinically asymptomatic patient undergoing treatment monitoring), optimizing the bowel by enterography technique leads to improved detection of inflammation and should be pursued if the patient can tolerate the oral contrast. On the other hand, CT with positive luminal contrast (without enterography technique) can identify wall thickening, luminal narrowing, and adjacent inflammatory changes that may be seen in CD [19]. In addition, the complications of abscess formation or fistula formation can be detected at standard IV contrast CT in which the positive oral contrast may improve detection of complications. Sensitivities for abscesses are very good, ranging from 86% to 100% [27,36]. There is more variable performance for fistula detection with sensitivities ranging from 68% to 100% [27,40,42]. One study showed a very low sensitivity of 20% for enteroenteric fistulas in their series [40]. Although standard abdomen and pelvis CT can be done either with or without the administration of IV contrast, it is evident that many of the processes seen with an acute flare in CD require IV contrast for optimal assessment. Without IV contrast, such processes can only be inferred by associated findings, such as wall thickening.