What investigations should be performed prior to surgery for large bowel obstruction?

The appropriate investigation prior to surgery for large bowel obstruction is a CT scan to exclude pseudo-obstruction. A CT scan provides detailed cross-sectional images of the abdomen, which can help identify the cause of the obstruction, such as tumors, strictures, or other abnormalities. It is also particularly useful for differentiating true obstructive pathology from pseudo-obstruction, which is a condition where the bowel appears obstructed radiographically but is not due to a physical blockage.

Using CT imaging allows for a comprehensive assessment of the entire abdomen and pelvis, providing critical information that can influence surgical planning. Additionally, it can help identify any associated complications, such as perforation or ischemia, which are critical considerations before proceeding with surgery.

In contrast, other imaging modalities such as ultrasound and MRI are less commonly used for evaluating bowel obstructions. A plain X-ray can give some initial information about bowel distension but is limited in its ability to provide a definitive diagnosis and is not as useful for planning surgical intervention. Similarly, a barium enema is generally not indicated in acute settings of suspected bowel obstruction, as it can risk further complication or delay urgent surgical treatment.