Imagine this clinical scenario: a client brings in their pet dog that is presenting with acute abdominal signs. After talking to the owner, you suspect an intestinal obstruction which, if diagnosed, could require surgical intervention. You recommend carrying out some diagnostic imaging tests to identify any intestinal obstructions, including an abdominal radiograph and ultrasonography.
Due to the client’s financial constraints, you can only use one diagnostic imaging method. You decide to consult the evidence to find out whether radiography or ultrasonography is superior at detecting the need for surgical intervention by accurately diagnosing small intestinal mechanical obstruction.
The evidence
Six studies were identified that tested the diagnostic validity of ultrasonography, radiography or both, when used to identify intestinal obstructions. Three papers were prospective cohort studies (Drost et al., 2016; Elser et al., 2020; Winter et al., 2017) that provided moderately strong evidence due to their study design. The other three had a cross-sectional design with a varied level of blinding, which produced weaker evidence (Shanaman et al., 2013; Sharma et al., 2010; Tyrrell and Beck, 2006).
Drost et al. (2016) and Elser et al. (2020) studied the diagnostic accuracy of radiography. The first paper examined 20 dogs that were diagnosed with mechanical intestinal obstruction and evaluated with radiography. The outcomes studied that are relevant to the research question were signs of gastrointestinal obstruction and diagnosis of mechanical obstruction. In comparison, Elser et al. studied 40 dogs with suspected gastrointestinal obstruction. The outcomes studied were sensitivity, specificity and percentage accuracy of the radiography.
Winter et al. (2017) was the only paper that studied the use of ultrasonography without radiography. The paper studied 16 dogs that were suspected of having a complete or partial gastrointestinal obstruction. The outcomes studied were sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ultrasonography in the diagnosis of gastrointestinal obstruction.
Shanaman et al. (2013), Sharma et al. (2010) and Tyrrell and Beck (2006) studied the use of both radiography and ultrasonography. Shanaman et al. examined 19 dogs that were admitted to hospital with abdominal signs, and Sharma et al. examined 82 dogs admitted to hospital with acute vomiting. The outcomes studied in both papers were the identification of clinical signs indicating obstruction. Tyrrell and Beck studied 11 dogs showing clinical signs of a gastrointestinal foreign body; the outcomes studied were the identification of foreign bodies.
Limitations of the evidence
Even among trained individuals, experience can have an impact on interpretation and decision making
There are some limitations to the papers studied, which means the overall strength of the evidence is moderate. Most of the studies had small sample sizes, with the exception of Sharma et al. (2010) which had a sample size of 82, while Drost et al. (2016) used a power calculation.
Five of the papers studied made some attempt at blinding, though some did so in a way that only partially reduced the possibility of bias. Winter et al. (2017) and Shanaman et al. (2013), for example, both made attempts at blinding that didn’t completely remove the possibility of bias, while Tyrrell and Beck (2006) were unable to blind due to their study design.
Another factor to consider was the impact that experience has on the effectiveness of diagnostic imaging technology. This can be seen in Elser et al. (2020), in which four trained radiologists reviewed diagnostic images but were at different stages of their career, ranging from a first-year radiology resident to a board-certified radiologist with 16 years of experience. There were disagreements between the group on their interpretations, which shows that even among trained individuals, experience can have an impact on interpretation and decision making.
Summary of findings
The papers that only studied one of the two diagnostic methods referred to in the research question had the following results. Drost et al. (2016) examined 20 dogs with radiography and found that sensitivity and specificity for the diagnosis of intestinal obstruction was 79.2 percent and 69.4 percent, respectively. Winter et al. (2017) examined 16 dogs with ultrasonography and found that the PPV of this diagnostic method was 93 percent, while sensitivity and specificity of abdominal ultrasound for diagnosis was 100 percent and 67 percent, respectively. Elser et al. (2020) found that the accuracy of diagnosis using radiography ranged from 70.2 to 89.5 percent in a mixed cohort of both cats and dogs.
The papers that studied both ultrasonography and radiography had the following results. Shanaman et al. (2013) found that both radiography and ultrasonography correctly identified eight out of nine (88.9 percent) cases as surgical. Both also achieved the same results on sensitivity (89 percent), specificity (100 percent), PPV (100 percent), NPV (89 percent) and accuracy (94 percent).
Sharma et al. (2010) found that radiography provided a definitive result in whether there was an obstruction in 58 out of 82 dogs (70.7 percent). On the other hand, ultrasonography provided a definitive result in whether there was an obstruction in 80 out of 82 dogs (97.6 percent).
Tyrrell and Beck (2006) found that 9 out of 16 (56 percent) cases of a foreign body were detected using radiography, although this cohort included five cats. On the other hand, 11 out of 11 (100 percent) of canine cases with foreign bodies were detected using ultrasound.
Conclusion
The evidence suggests that ultrasound has the potential to be superior to radiography at detecting intestinal obstructions in dogs with acute abdominal signs
There is moderate evidence to suggest that both radiology and ultrasound inform correct decision making for surgical intervention when used on dogs with suspected intestinal obstruction. The evidence suggests that ultrasound has the potential to be superior to radiography at detecting intestinal obstructions in dogs with acute abdominal signs. However, it must be noted that the experience of the observer correlates with the effective use of both radiography and ultrasonography, so imaging training is vital to help practitioners increase accuracy and confidence when using these tools to diagnose patients. Additionally, it must be noted that there were significant limitations within the studies observed, and there is a need for further research in this area that addresses these.
| The full Knowledge Summary can be read in RCVS Knowledge’s open access journal Veterinary Evidence. |
Disclaimer
The application of evidence into practice should take into account multiple factors, not limited to individual clinical expertise; patient’s circumstances and owner’s values; country, location or clinic where you work; the individual case in front of you; and the availability of therapies and resources.
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.
