Error and discrepancy in radiology: inevitable or avoidable?

It was recently estimated that one billion radiologic examinations are performed worldwide annually, most of which are interpreted by radiologists [1]. Most professional bodies would agree that all imaging procedures should include an expert radiologist’s opinion, given by means of a written report [2]. This activity constitutes much of the daily work of practising radiologists. We don’t always get it right. Although not always appreciated by the public, or indeed by referring doctors, radiologists’ reports should not be expected to be definitive or incontrovertible. They represent clinical consultations, resulting in opinions which are conclusions arrived at after weighing of evidence [3]; “opinion” can be defined as “a view held about a particular subject or point; a judgement formed; a belief” [4]. Sometimes it is possible to be definitive in radiological diagnoses, but in most cases, radiological interpretation is heavily influenced by the clinical circumstances of the patient, relevant past history and previous imaging, and myriad other factors, including biases of which we may not be aware. Radiological studies do not come with inbuilt labels denoting the most significant abnormalities, and interpreting them is not a binary process (normal vs abnormal, cancer vs “all-clear”). In this context, defining what constitutes radiological error is not straightforward. The use of the term “error” implies that there is no potential for disagreement about what is “correct”, and indicates that the reporting radiologist should have been able to make the correct diagnosis or report, but did not [3]. In real life, there is frequently room for legitimate differences of opinion about diagnoses or for “failure” to identify an abnormality that can be seen in retrospect. Expert opinion often forms the basis for deciding whether an error has been made [3], but it should be noted that “experts” themselves may also be subject to question (“An expert is someone who is more than fifty miles from home, has no responsibility for implementing the advice he gives, and shows slides.” - Ed Meese, US Attorney General 1985–88). Any discrepancy in interpretation that deviates substantially from a consensus of one’s peers is a reasonable and commonly accepted definition of interpretive radiological error [1], but even this is a loose description of a complex process, and may be subject to debate in individual circumstances. Certainly, in some circumstances, diagnoses are proven by pathologic examination of surgical or autopsy material, and this proof can be used to evaluate prior radiological diagnoses [1], but this is not a common basis for determining whether error has occurred. Many cases of supposed error, in fact, fall within the realm of reasonable differences of opinions between conscientious practitioners. “Discrepancy” is a better term to describe what happens in many such cases. This is not to suggest that radiological error does not occur; it does, and frequently. Just how frequently will be addressed in another section of this paper. Negligence Leonard Berlin, writing in 1995, found that the rate of radiology-related malpractice lawsuits in Cook County, Illinois, USA, was rising inexorably, with the majority of suits for missed diagnosis, and we have no reason to believe that this pattern has since changed. Interestingly, his data showed a progressive reduction in the length of time between the introduction of a new imaging technology and the first filed lawsuit arising from its use, from over 10 years for ultrasound (first suit 1982), to 8 years for CT (first suit 1982), and 4 years for MRI (first suit 1987) [5]. The distinction between “acceptably” or “understandably” failing to perceive or report an abnormality on a radiological study and negligently failing to report a lesion is an important one, albeit one that is difficult to explain to laypersons or juries. As Berlin wrote: “[F]rom a practical point of view once an abnormality on a radiograph is pointed out and becomes so obvious that lay persons sitting as jurors can see it, it is not easy to convince them that a radiologist who is trained and paid for seeing the lesion should be exonerated for missing it. This is especially true when the missing of that lesion has delayed the timely diagnosis and the possible cure of a malignancy that is eventually fatal” [6]. A major influence on the determination of whether an initially missed abnormality should have been identified arises in the form of hindsight bias, defined as the “tendency for people with knowledge of the actual outcome of an event to believe falsely that they would have predicted the outcome” [6]. This “creeping determinism” involves automatic and immediate integration of information about the outcome into one’s knowledge of events preceding the outcome [6]. Expert witnesses are frequently influenced by their knowledge of the outcome in determining whether a radiologist, acting reasonably, ought to have detected an abnormality when reporting a study prior to the outcome being known, and thus in suggesting whether failure to detect the abnormality constituted negligence. Berlin quotes a Wisconsin (USA) appeals court decision which helpfully teases out some of these points: “In determining whether a physician was negligent, the question is not whether a reasonable physician, or an average physician, should have detected the abnormalities, but whether the physician used the degree of skill and care that a reasonable physician, or an average physician, would use in the same or similar circumstances…A radiologist may review an x-ray using the degree of care of a reasonable radiologist, but fail to detect an abnormality that, on average, would have been found… Radiologists simply cannot detect all abnormalities on all x-rays… The phenomena of “errors in perception” occur when a radiologist diligently reviews an x-ray, follow[s] all the proper procedures, and use[s] all the proper techniques, and fails to perceive an abnormality, which, in retrospect is apparent… Errors in perception by radiologists viewing x-rays occur in the absence of negligence” [6]. Radiologists base their conclusions on a varying number of premises (e.g. available clinical information, statistical likelihood). Any of the bases for conclusions may prove to have been false. Subsequent information may show the original conclusion to have been false, but this does not constitute a prima facie error in judgement, and the possibility that a different radiologist might have come to a different conclusion based upon the same information does not imply negligence on its own [7]. It is important to avoid the temptation (beloved by plaintiffs’ lawyers) to apply the principle “radiologists have a duty to interpret radiographs correctly” to specific instances (“radiologists have a duty to interpret this particular radiograph correctly”). The inference that missing an abnormality on a specific radiograph automatically constitutes malpractice is not correct [7]. Experienced, competent radiologists may miss abnormalities, and may be unaware of having done so. Experienced radiologists may make different judgements based on the same study; thus differences in judgement are not negligence [7]. Unfortunately, juries are often swayed by compassion for an injured defendant, and research has shown that the results of malpractice suits are often related to the degree of disability or injury rather than to the nature of the event or whether physician negligence was present [7].