Review of CT scout view can unveil significant pathologic findings not included in the CT field of view (FOV), according to a study published in the June issue of the American Journal of Roentgenology.
The CT scout view has been overlooked since the advent of CT and a recent medicolegal case spurred lead author Pamela T. Johnson, MD, of the Johns Hopkins Hospital in Baltimore, and colleagues to review literature for investigations on the scout view’s utility. After discovering conflicting evidence, the researchers performed a systematic analysis with a large sample size to determine the frequency and type of additional diagnostic information offered by a scout view that cannot be identified on the CT study.
During the study, two radiologists were blinded to the history and CT findings of 2,032 scout views that were retrospectively reviewed. When necessary, all cases with major findings were correlated with the CT study, another imaging study or medical record by a third radiologist to assess the validity of the scout view finding and whether it was identifiable on the CT study.
Major findings were found in 257 of the cases reviewed by reader one and 436 cases reviewed by reader two. The CT study confirmed 69 to 78 percent of the scout findings and refuted 13 to 16 percent. Fifteen of reader one’s major findings and 48 of reader two’s major findings were not included in the CT FOV.
Five and 21 of the readers' respective findings constituted a missed pathologic finding. The most common finding was cardiomegaly detected on a nonchest CT scout view. Other pathologic findings included fracture, metastasis, avascular necrosis or subluxation of the humeral head, dilated bowel and thoracic aortic dilation. The most common false-positive finding was cardiomegaly.
"Our results support routine review of the anatomic region on the scout view that are not imaged on CT and suggest that interpreting the scout view will not generate unnecessary testing if the limitations of the scout view are recognized,” wrote the study’s authors.
They suggest future investigations to determine the utility of the scout view according to the anatomic location being imaged.
In an associated editorial, Leonard Berlin, MD, of Skokie Hospital in Skokie, Ill., emphasizes the importance of Johnson et al’s findings and draws attention to their medicolegal and ethical implications.
“Although 2 percent appears to be a low percentage, extrapolating Johnson et al’s data to the 85 million patients who undergo CT each year means that as many as 1.7 million patients may have a major abnormal finding that is seen on a scout view but not on the related axial CT images,” wrote Berlin.
Berlin cites a case to illustrate the importance of routinely reviewing CT scout views. After falling off of a bicycle and hitting his head on a sidewalk, a 3 year-old boy was taken to the emergency department at a local hospital. The patient was dazed, but his neurologic exam appeared to be normal. The boy underwent an un-enhanced head CT whose results were interpreted as normal by a hospital staff radiologist. The boy was discharged with a diagnosis of a mild concussion but returned within two hours convulsing. He underwent another unenhanced head CT exam that revealed a large epidural hematoma with a linear parietal bone fracture. Although emergency surgery was performed, the patient died.
The boy’s family filed a medical malpractice suit against the emergency department physician and radiologist. During the trial, the radiologist acknowledged that he did not look at the scout view that accompanied the initial CT scan, which showed a large linear parietal bone fracture.
“It is not known with any degree of accuracy what percentage of radiologists ignore rather than review the CT scout image. Anecdotally Johnson et al and I have found that a sizeable percentage of radiologists fail to review the scout images," wrote Berlin. "Johnson et al concluded that their findings support the routine review of the scout view when interpreting a CT study. Reasonable medical practice, logic, and medicolegal as well as ethical considerations confirm their conclusion."