However, patient factors such as obesity and guarding, especially in the acutely ill scenario, may preclude adequate compression with the US probe. In addition, large amounts of shadowing gas may obscure bowel, preventing an optimal examination. Location of bowel involvement affects diagnosis with higher sensitivities for terminal ileal involvement detection as compared with more proximal small bowel disease [87]. False-positive diagnoses of abscesses are more likely at US [97]. The determination for alternative etiologies may also be decreased as compared with CT or MRI. HMPAO WBC Scan Leucoscintigraphy or Tc-99m-hexamethyl propylene amine oxime-labeled white blood cell (Tc-99m HMPAO WBC) scan have demonstrated good sensitivities and specificities for intestinal inflammation in the 79% to 85% and 81% to 98% range, respectively [98]. Proponents contend that leucoscintigraphy is useful in the diagnosis and evaluation of activity of extent of disease [99] with performance results equivalent to cross-sectional imaging [28]. However, the disadvantages of this examination, such as the decreased ability to depict and therefore detect alternative diagnoses and the complicated time-consuming technical aspects (ie, labeling and handling of blood products) have limited its use in initial diagnosis. Furthermore, leucoscintigraphy is limited in alternative diagnoses mimicking CD. FDG-PET/CT Skull Base to Mid-Thigh The addition of metabolic information from PET with the morphologic anatomic imaging of CT or MR shows promise. It may be helpful to better assess the level of active inflammation from fibrosis [100,101]. Studies also show improved assessment in the colon in a murine animal model [102], which points to potential future usefulness because the colon is less well evaluated at both CT enterography and MR enterography. At this point, there are few large-series published clinical studies but small series show promising results [103,104]. Variant 2: Known Crohn disease, suspected acute exacerbation.
Crohn Disease. However, patient factors such as obesity and guarding, especially in the acutely ill scenario, may preclude adequate compression with the US probe. In addition, large amounts of shadowing gas may obscure bowel, preventing an optimal examination. Location of bowel involvement affects diagnosis with higher sensitivities for terminal ileal involvement detection as compared with more proximal small bowel disease [87]. False-positive diagnoses of abscesses are more likely at US [97]. The determination for alternative etiologies may also be decreased as compared with CT or MRI. HMPAO WBC Scan Leucoscintigraphy or Tc-99m-hexamethyl propylene amine oxime-labeled white blood cell (Tc-99m HMPAO WBC) scan have demonstrated good sensitivities and specificities for intestinal inflammation in the 79% to 85% and 81% to 98% range, respectively [98]. Proponents contend that leucoscintigraphy is useful in the diagnosis and evaluation of activity of extent of disease [99] with performance results equivalent to cross-sectional imaging [28]. However, the disadvantages of this examination, such as the decreased ability to depict and therefore detect alternative diagnoses and the complicated time-consuming technical aspects (ie, labeling and handling of blood products) have limited its use in initial diagnosis. Furthermore, leucoscintigraphy is limited in alternative diagnoses mimicking CD. FDG-PET/CT Skull Base to Mid-Thigh The addition of metabolic information from PET with the morphologic anatomic imaging of CT or MR shows promise. It may be helpful to better assess the level of active inflammation from fibrosis [100,101]. Studies also show improved assessment in the colon in a murine animal model [102], which points to potential future usefulness because the colon is less well evaluated at both CT enterography and MR enterography. At this point, there are few large-series published clinical studies but small series show promising results [103,104]. Variant 2: Known Crohn disease, suspected acute exacerbation.