Can abdominal ultrasound (abdominal ultrasonography) identify rectal bleeding?

From the Guidelines

Abdominal ultrasound is not a reliable method for identifying rectal bleeding due to its limitations in visualizing the lower gastrointestinal tract, particularly the rectum. The primary issue with using abdominal ultrasound for this purpose is that ultrasound waves cannot effectively penetrate through gas-filled bowel loops, creating significant technical limitations in visualizing the intestinal tract 1. Furthermore, the rectum's location deep in the pelvis makes it difficult to assess adequately with an abdominal ultrasound.

Some of the key limitations of abdominal ultrasound in the context of trauma and internal injuries include its inability to identify certain types of injuries such as contained solid organ injuries, mesenteric vascular injuries, hollow viscus injuries, and diaphragmatic injuries, as well as its low sensitivity for detecting free intra-peritoneal fluid in penetrating torso trauma and in blunt abdominal trauma in children 1.

Given these limitations, rectal bleeding requires more specific diagnostic approaches such as colonoscopy, sigmoidoscopy, or anoscopy, which allow direct visualization of the bleeding source. Other more appropriate imaging studies for investigating rectal bleeding might include CT scans, MRI, or nuclear medicine studies like tagged red blood cell scans, especially for active bleeding 1.

In clinical practice, if a patient presents with rectal bleeding, they should undergo a physical examination including digital rectal exam and appropriate endoscopic evaluation rather than relying on abdominal ultrasound as the primary diagnostic tool. The use of abdominal ultrasound might be considered in the initial assessment of patients with suspected abdominal trauma to quickly identify free intra-abdominal fluid, but its findings should be interpreted with caution and in conjunction with other diagnostic modalities and clinical assessments 1.

Key points to consider in the diagnostic approach to rectal bleeding include:

• The need for direct visualization of the bleeding source through endoscopy
• The limitations of abdominal ultrasound in evaluating the lower gastrointestinal tract
• The potential role of other imaging studies like CT scans, MRI, or nuclear medicine studies in certain cases
• The importance of a thorough physical examination, including digital rectal exam, in the initial assessment of patients with rectal bleeding.

From the Research

Abdominal Ultrasound and Rectal Bleeding

• Abdominal ultrasound can be used to identify rectal bleeding, but its effectiveness varies depending on the location and cause of the bleeding 2.
• A study published in 2006 found that transabdominal ultrasound was able to localize the bleeding site in 66% of patients with lower gastrointestinal bleeding, but its detectability was lower for rectal bleeding (30%) compared to other locations (82-100%) 2.
• Another study published in 2013 discussed the role of MDCT and CT angiography in evaluating rectal bleeding, but did not mention abdominal ultrasound as a diagnostic tool for this condition 3.
• Digital rectal examination has been shown to be an important diagnostic tool for identifying rectal bleeding and malignancies, and can reduce hospital admissions, endoscopies, and medical therapy in patients with acute gastrointestinal bleeding 4, 5.

Limitations of Abdominal Ultrasound

• Abdominal ultrasound may not be effective in diagnosing rectal bleeding caused by certain conditions, such as diverticular bleeding or rectal varices 2.
• The usefulness of abdominal ultrasound for diagnosing lower gastrointestinal bleeding is not fully established, and colonoscopy remains the first-line modality for diagnosis 3, 2.

Alternative Diagnostic Tools

• MDCT and CT angiography have been shown to be valuable diagnostic tools for evaluating rectal bleeding, particularly in patients with active bleeding and hemodynamic instability 3.
• Digital rectal examination is an important diagnostic tool for identifying rectal bleeding and malignancies, and can be used in conjunction with other diagnostic modalities such as colonoscopy and abdominal ultrasound 4, 5.