Diagnostic/perception error has been defined as a diagnosis that is missed, delayed or wrong as determined by a subsequent definitive test or finding. The lack of perception of a normal finding may also constitute a diagnostic error when clinically relevant. Initial work by Garland in 1949, who estimated an average radiology perception error rate of up to 30%, has led to extensive study in human perception and factors in perception error which, for the most part, remain poorly understood [4, 7, 8]. Increasing workloads, cognitive biases, systemic factors such as lighting, along with rising quality expectations are potential yet minor factors that contribute to perception error, often the result of mental or visual fatigue [1, 3, 5]. Attempts to improve error by work hour alterations, improved environmental setting such as decreased interruptions and changes in luminescence of monitors have had limited success [5].
Errors in imaging have been classified into two broad categories comprising errors in perception versus interpretive errors. Perception error accounts for 60–80% of radiologists errors in clinical practice. The majority lacks any identifiable cause [5, 9]. The persistence of investigative studies depicting the degree of perceptual error among imagers worldwide despite the level of training or experience and spanning multiple modalities would suggest that errors related to carelessness, negligence or underperformance of some kind are not the typical cause. Rather, there appears to be an inherent misperception or under perception associated with the complex process of image interpretation perhaps below the threshold of conscious awareness [5]. More recent studies have further defined perceptual error into three basic types. These include (1) scanning error—a failure to fixate on the adequate region; (2) recognition error—a fixation on the region but for inadequate time and (3) decision-making error—fixation on the appropriate region for adequate time, but an unexplained lack of recognition of pathology [3]. We believe that a lack of perception of a normal finding during the scanning process, rather than the usual lack of recognition on a set of provided images, that will alter patient care and management should be included in this third type.
Previous studies have shown the value of sonographer experience in patient diagnosis [10,11,12]. Our study hopes to also illustrate the role of an inherent perceptual skill that some sonographers display that can affect patient care. Missed and misinterpreted diagnosis in sonography are often too easily attributed to technical factors such as body habitus or overlying bowel gas. While these factors may limit an examination, the sonographer’s ability to adequately perceive anatomic fascial planes in the region of concern will often determine the ultimate clinical value of the study. Intuitively, one would expect that increased experience (years of training) in scanning or increase in knowledge base (as one would expect the senior residents to have gained more imaging knowledge than the juniors) would correlate with an improved ability to perceive the normal appendix. We found this to be the case, as our junior residents demonstrated a lower ability to identify the normal appendix as compared to their more senior colleagues. Although in general, sonographers with more years of experience correlated with an increase in perceiving the normal appendix, within the group of experienced sonographers there was a wide discrepancy in frequency of perception of a normal appendix suggesting there may be an inherent individual perceptual skill. Just as some radiologists are able to more quickly spot the lung nodule on chest radiographs or the individual who is able to perceive “Waldo” more easily than others, we suggest that there are sonographers that find the normal appendix more easily than others [13].
Utilizing the “query” appendicitis ER population illustrates the potential clinical effect of this difference in sonographer perceptual skill. Demonstration of a normal appendix on sonography can, for the most part, eliminate this potentially dangerous disease process from the physician’s list of concern, potentially saving the patient from further studies such as CT/MR and expediting patient care through the emergency department. Interestingly, if all the patients sent to the imaging department to rule out appendicitis could have been triaged to the four sonographers with the greatest success in perceiving the normal appendix, an additional 50 patients would have had their appendix visualized, and the overall percentage of cases where the appendix was not seen would drop from 52 to 12%. As such, it may be of benefit for less experienced sonographers to accompany sonographers who are more experienced to gain experience and technical skills in visualizing the appendix. Alternatively, this discrepancy in sonographer perceptual skill may suggest that triaging query appendicitis cases to a set of sonographers more adept than others may result in higher efficiency and a decrease in unnecessary further testing for the patient.
The study has multiple limitations which need to be acknowledged. We are a relative small center which resulted in variable and sometimes insufficient number of cases for adequate assessment of each sonographer and an overall small sample volume. The body mass index (BMI) was not utilized, which may affect the ability to see the appendix. As the patients were referred to the department without direction to a specific sonographer it was felt that over time the differences in BMI would likely equalize out among the scanners. Further limitations were a potential bias related to the sonographer choosing not to perform a ‘query’ appendicitis case deferring to a sonographer with more confidence if possible. In addition, the ability of the staff radiologists to perceive the normal appendix was not assessed. Given, we are at an academic center, the majority of the ER cases sent to the department were initially performed by the trained sonographers who then present the case to the radiology resident on service. The cases may not be reviewed initially by the staff unless a concern or question is raised by the resident. Additionally, the cases are often performed after hours with the resident on-call or available sonographer. It is possible that availability of staff radiologists may have improved detection of the normal appendix. Lastly, a further limitation was utilizing the initial sonography image recorded on the PACS images as the start of the exam as this may not take into account the full time the sonographer took to perform a “scout” scan before acquiring images.
