From the Guidelines
Abdominal ultrasound is not the recommended test for identifying colon cancer. While an ultrasound can visualize some abdominal structures, it has significant limitations in detecting colon cancer because sound waves cannot penetrate air-filled intestines effectively, and the colon's deep location makes visualization difficult 1. For proper colon cancer screening and diagnosis, colonoscopy remains the gold standard as it allows direct visualization of the entire colon and removal of suspicious polyps. Other more appropriate tests include CT colonography (virtual colonoscopy), flexible sigmoidoscopy, or stool-based tests like FIT or Cologuard.
According to the most recent guidelines, a total colonoscopy is recommended for diagnostic confirmation of colon cancer and to rule out synchronous tumours 1. CT of the thoracic, abdominal and pelvic cavities with i.v. contrast administration is the preferred radiological method for the evaluation of the extent of CRC 1. In some cases, an ultrasound might incidentally detect large masses or metastatic spread to the liver from colon cancer, but it should not be used as a primary screening or diagnostic tool for colorectal malignancies.
The use of abdominal ultrasound is not explicitly recommended for the diagnosis of colon cancer in the provided guidelines 1. Instead, it is mentioned that ultrasonography of the liver and the whole abdomen may be useful, but a CT scan is usually more appropriate for detecting metastatic spread to the liver or complications related to the tumour 1. Therefore, colonoscopy and CT scans are the preferred diagnostic tools for colon cancer, and abdominal ultrasound should not be relied upon for primary screening or diagnosis.
From the Research
Abdominal Ultrasound and Colon Cancer Diagnosis
- Abdominal ultrasound can be used to identify colon cancer, with a sensitivity of 79.06% and a specificity of 92.15% 2.
- The positive predictive value (PPV) and negative predictive value (NPV) of abdominal ultrasound in diagnosing colon cancer are 80.9% and 91.2%, respectively 2.
- Excluding lesions of the rectal ampulla, the sensitivity, specificity, PPV, and NPV of abdominal ultrasound increase to 91.8%, 92.1%, 80.9%, and 96.9%, respectively 2.
Comparison with Other Diagnostic Methods
- Abdominal ultrasound has been compared to colonoscopy, CT, and PET/CT in diagnosing colon cancer, with varying results 3, 4, 5.
- A study found that ultrasound and CT had a sensitivity of 100% in detecting colon cancer, but were poor at diagnosing polyps 4.
- Another study found that PET/CT colonography was at least equivalent to CT + PET for tumor staging in patients with colorectal cancer 5.
Factors Affecting Detection
- The detection of colorectal cancer and colon polyps on screening abdominal ultrasonography is affected by factors such as lesion size and depth of invasion 6.
- Wall thickening may be a consequence of cancer cells invading below the subserosa, making lesions detectable on abdominal ultrasound 6.