In a study titled Unexpected Findings in Complete Versus Partial Ultrasound Examinations researchers found that there will be an unacceptable rate of missed significant findings in limited ultrasound examinations.
In that study, 785 abdominal ultrasound examinations were performed on canine and feline patients. Unexpected findings were found in 228 (29%) of cases. Of those 228 unexpected findings, 133 (58.7%) were considered clinically significant. Therefore, clinically significant unexpected findings were found in 16.9% of the total 785 cases.
My clinical experience supports this study. This is why I discourage limited abdominal ultrasound studies.
The situation in veterinary medicine is different than in human medicine where limited studies are commonly performed. In human medicine, ultrasound is often used as an adjunct imaging modality with other studies such as CT or MRI of the abdomen. Conversely, in veterinary medicine, abdominal ultrasound is often the primary and many times only imaging study that will be performed. Furthermore, in veterinary medicine, abdominal ultrasound is often performed in older patients that may have more than one problem or lesion.
In conclusion, the risk of missing a significant unexpected lesion in the abdomen is not worth the small benefit of saving the client a few dollars.
Reference: Henry, G.A. Unexpected Findings in Complete Versus Partial Ultrasound Examinations. Proc. Am. Coll. Vet. Radiol. 2001. http://www.acvr.ucdavis.edu/activities/meetings/hawaii01/hawaii.pdf
(This article originally appeard in a 2006 MVMA newsletter)