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Does Ultrasound Miss Abdominal Lesions?

November 7, 2007 Leave a comment

Of course it does. But big question is how often? Are some findings more or less reliable?

An interesting article in the recent JAAHA looks at the correlation of abdominal ultrasound findings with gross surgical exploration. Whenever I have access to the ex lap findings of a patient undergoing an explore after one of my ultrasounds, I am anxious to find out how my findings compare. We all fear a negative explore, although almost every patient I can think of who had a negative gross explore, had microscopic lesions that were helpful in patient management. Following up on the ultrasound findings is an essential part of the learning process for anyone performing ultrasound or ordering one for their patient.

This was a retrospective study looking at cases from The Queen Mother Hospital for Animals in the UK. The ultrasounds were performed by experienced radiologists or radiology residents. They looked at 100 cases who had an ex lap within 48 hours of an abdominal ultrasound. There were only 19 cats, so one has wonder whether this was an adequate sample size for this particular species. There were no stats looking at cats versus dogs. However, they did note that there was “no apparent relationship…detected between body size of animal and the sensitivity of ultrasound for the primary lesion.” I find cats much easier to ultrasound than similarly-sized dogs (perhaps that is my bias towards this fabulous species), but I do feel this is a weakness in the study.

Their results are similar to what I have found in my clinical practice:

100 primary lesions & 67 secondary lesions were found at surgery.

Ultrasound did not detect the primary lesion in 24 of these animals and secondary lesions in 11 animals.

“A total of 36 animals [out of 100] had discordant ultrasonographic and surgical findings of their primary and secondary lesions.”

Ultrasound detected peritonitis lesions in 89% of cases.

Ultrasound detected intestinal obstruction in 64% of cases.

Ultrasound detected hepatic or splenic nodules in 63% of cases.

GI lesions were most likely to be missed by ultrasound (perforations, ulcerations) followed by organomegaly.

Although not statistically significant, ultrasound missed 5 GI foreign bodies.

Gross visualization at surgery missed some lesions seen on ultrasound – prostatic cysts, renal lesions, bladder lesions, splenic/liver lesions, and a gall bladder polyp.

This study brings to light my own experience.

If I am presented with a persistently vomiting animal with radiographs that are very suspicious for a GI obstruction but my ultrasound findings do not suggest obstruction – I ALWAYS err on the side of suspecting obstruction. Depending on the status of the animal and the level of suspicion from the radiographs, the next step may be to continue supportive care and repeat rads in 6-12 hours or it may be an exploratory laparotomy. My own cat had a negative explore and a number of my patients have as well. We have always learned something from the biopsies obtained and I have been fortunate to never have an owner be angry about it. The possibility of a negative explore is an important part of my conversation with the owner prior to surgery.

When ultrasound is used as part of check for metastasis, again, I always warn owners that we may be missing something. Ultrasound is notoriously poor at seeing all lesions in a liver or spleen. It may miss a focal intestinal lesion. I cannot count how many times over the course of my residency that Mike Willard showed me pictures of horrid livers at laparoscopy that were deemed normal by very experienced radiologists. Likewise, as was seen in this study, ultrasound may be able to detect architectural irregularities in an organ (especially liver, spleen, kidney) that are not seen on the surface of the organ at surgery. In these cases, a biopsy of a “normal” organ may reveal significant pathology.

This is why I am an annoyance to the surgeons when they explore the abdomens of my patients. Ultrasound is so subjective. It helps to have the objective look at surgery (or necropsy) to verify what I have seen. I am quick to recommend surgery (unless it would be detrimental to the patient) when I have any doubt about what I am seeing with ultrasound or if the animal’s signs are worse than expected based on ultrasound. Until we get a hold of one of Dr. Crusher’s tricorders, we’re stuck with histopathology for a diagnosis in many patients.

Jennifer S. Fryer, DVM

www. veterinaryanswers.com

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