What is the most appropriate investigation for a 56-year-old man presenting with absolute constipation, rectal bleeding, and a dilated colon with small bowel dilatation on conventional abdominal x-ray (radiograph)?

From the Guidelines

The most appropriate investigation for this 56-year-old man with absolute constipation, rectal bleeding, abdominal distension, empty rectum on digital examination, and radiographic findings of dilated colon and small bowel is option D, Conventional CT scan. A conventional CT scan is the preferred initial investigation because it can rapidly identify the cause of large bowel obstruction while also evaluating for potential complications such as perforation or ischemia, as supported by the study published in the World Journal of Emergency Surgery in 2019 1. This patient's presentation suggests a large bowel obstruction, possibly due to colorectal cancer, and the CT scan can visualize the site of obstruction, assess for masses, and determine the extent of bowel dilatation. While colonoscopy might eventually be needed for tissue diagnosis, it is contraindicated in acute obstruction due to the risk of perforation. CT colonography requires bowel preparation which is inappropriate in obstruction, and CT enteroclysis focuses primarily on small bowel pathology rather than colonic disease. The conventional CT scan provides comprehensive information about intra-abdominal pathology without requiring bowel preparation, making it the safest and most informative initial investigation for this clinical scenario, and is in line with the recommendations for suspected small-bowel obstruction as outlined in the Journal of the American College of Radiology in 2020 1. Some key points to consider include:

• The ability of CT scans to provide information about the underlying cause of obstruction or alternative diagnoses if no signs of bowel obstruction are present 1
• The superiority of CT scans with intravenous contrast over conventional abdominal radiography and ultrasound in diagnostic accuracy 1
• The importance of identifying ischemia and necrosis, especially in adhesive small bowel obstruction and sigmoid volvulus, which can be accurately evaluated with CT scans 1

From the Research

Diagnostic Approach

The patient presents with symptoms of absolute constipation, rectal bleeding, and a distended abdomen, which suggests a possible bowel obstruction. The digital rectal examination reveals an empty rectum, and the conventional abdominal x-ray shows a dilated colon with associated dilatation of the small bowel.

Investigation Options

The most appropriate investigation for this patient would be:

• CT enteroclysis, as it is a sensitive and specific test for detecting small bowel obstruction and can also help identify the cause of the obstruction 2, 3, 4.
• This test is particularly useful in evaluating the small bowel and can provide detailed images of the bowel lumen and wall.
• CT enteroclysis has been shown to be superior to other imaging tests, such as conventional CT and barium enteroclysis, in the diagnosis of small bowel obstruction 3.

Rationale

The use of CT enteroclysis is supported by studies that demonstrate its effectiveness in diagnosing small bowel obstruction and identifying the cause of the obstruction 2, 3, 4. Additionally, CT enteroclysis can provide detailed images of the bowel lumen and wall, which can help identify other potential causes of the patient's symptoms, such as tumors or inflammatory bowel disease. In contrast, conventional CT scan may not provide sufficient detail to diagnose small bowel obstruction, and colonoscopy may not be suitable for evaluating the small bowel 5. CT colonography is also not the most appropriate test in this case, as it is primarily used for detecting colon cancer and may not provide sufficient information about the small bowel.