Patients with suspected intermittent or low-grade SBO may have a more indolent presentation in which the patient may be asymptomatic at baseline with intermittent symptoms. If a SBO is present, it may be intermittent or very low-grade, requiring provocative measures such as bowel distention to visualize this process on a consistent basis. In low-grade SBO, there is sufficient luminal patency to allow contrast to flow beyond the point of obstruction. Low-grade or intermittent SBO can therefore be more difficult to diagnose with modalities that do not maximally distend or exaggerate the caliber of the small-bowel lumen. The patient may be relatively asymptomatic and with a more nonspecific presentation with other differential considerations possible. On imaging, it may be difficult to visualize dilated abnormal loops and a transition point. In these cases, volume-challenge or dynamic enteral examinations may be preferred to accentuate mild or subclinical obstructions and to better challenge the distensibility of small-bowel. The multiplanar reformatting capabilities of multidetector CT scanners has also helped in evaluating these patients. CT Abdomen and Pelvis Although standard abdominal and pelvic CT examinations in patients with a suspected high-grade SBO have shown diagnostic accuracies of greater than 90% [4,5,17], low-grade or intermittent obstruction has been less accurately diagnosed with a sensitivity of only 48% to 50% and a specificity of 94% [7,80]. In this situation of suspected intermittent or low-grade SBO, the bowel loops may look unremarkable with intrinsic enteral fluid or standard oral contrast administration at CT. Oral contrast may be purposefully given to these patients when SBO is a consideration. When a transition point is identified without passage of orally administered positive contrast, optional re-imaging within 24 hours may depict passage of oral contrast beyond the transition point, indicating incomplete or partial obstruction [81].
Suspected Small Bowel Obstruction. Patients with suspected intermittent or low-grade SBO may have a more indolent presentation in which the patient may be asymptomatic at baseline with intermittent symptoms. If a SBO is present, it may be intermittent or very low-grade, requiring provocative measures such as bowel distention to visualize this process on a consistent basis. In low-grade SBO, there is sufficient luminal patency to allow contrast to flow beyond the point of obstruction. Low-grade or intermittent SBO can therefore be more difficult to diagnose with modalities that do not maximally distend or exaggerate the caliber of the small-bowel lumen. The patient may be relatively asymptomatic and with a more nonspecific presentation with other differential considerations possible. On imaging, it may be difficult to visualize dilated abnormal loops and a transition point. In these cases, volume-challenge or dynamic enteral examinations may be preferred to accentuate mild or subclinical obstructions and to better challenge the distensibility of small-bowel. The multiplanar reformatting capabilities of multidetector CT scanners has also helped in evaluating these patients. CT Abdomen and Pelvis Although standard abdominal and pelvic CT examinations in patients with a suspected high-grade SBO have shown diagnostic accuracies of greater than 90% [4,5,17], low-grade or intermittent obstruction has been less accurately diagnosed with a sensitivity of only 48% to 50% and a specificity of 94% [7,80]. In this situation of suspected intermittent or low-grade SBO, the bowel loops may look unremarkable with intrinsic enteral fluid or standard oral contrast administration at CT. Oral contrast may be purposefully given to these patients when SBO is a consideration. When a transition point is identified without passage of orally administered positive contrast, optional re-imaging within 24 hours may depict passage of oral contrast beyond the transition point, indicating incomplete or partial obstruction [81].