Nick R Anthonisen
In the present issue of the Canadian Respiratory Journal, Turner et al (pages 311–316) describe a prospective study of thoracic computed tomography (CT) scanning at Vancouver General Hospital (Vancouver, British Columbia). They essentially described the hospital’s workload of thoracic CT scans, and used a pre- and postscan questionnaire to assess the diagnostic impact of the scan findings and the appropriateness of the timing of the scan according to priorities that ranged from ‘elective’ to ‘emergency’. They were able to collect usable data – pre- and postscan questionnaire results – from 62% of the patients examined, amounting to 454 cases. This is a substantial number, which I interpret as indicating a high level of cooperation between the radiologists and the referring physicians who filled out the questionnaires.
Many of their results were predictable, I think, given the environment. Most scans were ordered by respirologists, with thoracic surgeons coming in second. Most, especially those carried out in outpatients, were for diagnostic purposes as opposed to observing the progress of a known disease. Surgeons were more likely to order scans for staging, and respirologists for diagnosis. Indications and wait times differed substantially between inpatients and outpatients.
Impacts were assessed in terms of whether the initial diagnosis was changed by the scan result; in 52% of cases, this did not occur, while in 48%, it did. One-quarter of the scans were normal and, in 23%, the diagnosis was changed from one disease to another. In 56% of cases, referring physicians indicated that the results of the scan generated important new information. Although I am sure that these results are accurate and reflect the major contribution that CT scans make to the current diagnosis of lung diseases (see below), I believe the ‘change versus nonchange’ dichotomy is an oversimplified view of clinical decision-making. No one is going to send in a CT requisition with a working diagnosis of ‘normal’, although I am sure that many were ordered to see if they were in fact normal. A particularly good example of this is the suspicion of pulmonary embolism: 68% of the scans investigating this disease were normal, and I am sure that many were performed precisely to ascertain if this was the case. The case is similar for many of the scans for nodules and interstitial lung diseases, other major contributors to the normal category. It would also be somewhat surprising if in the cases in which the disease category was changed, the new diagnosis had not been considered by the referring physician. Turner et al tried to get a feel for this kind of situation by asking about the confidence of the referring physician in the initial and subsequent diagnoses, but this is a tricky business, and results were not very striking. The largest increase in confidence occurred when scans were normal, as may have been expected given the sensitivity of the technique. I should note that the above criticisms are relatively easy to make, but it would be extremely difficult to design a study that answered them in a comprehensive way in a large series of cases.
Of equal interest was the analysis of the time between receipt of the requisition for the CT scan and its execution. Elective cases had a mean wait time of approximately 30 days, while moderate and urgent cases waited less than one week. The wait time for suspected cancer was 12 to 14 days. The referring physician prioritized individual patients, and the results indicate a high degree of concurrence on the part of the radiologists with or without informal communication. In only 4% of cases did the referring physicians feel that the scan was overly delayed. The authors characterize this as reflecting the Canadian health care system. I hope this is the case.
Finally, I must comment that thoracic CT scans are a major advance in the diagnosis of lung disease. They give fantastic anatomical detail and because of this are (I think) easier to read than chest x-rays. They are absolutely essential in the diagnosis and management of lung cancer, interstitial disease and pulmonary embolism, at least. Presumably because of this, they have become much easier to obtain as the number of available scanners has grown; I have no problem in getting prompt outpatient scans in my patients with interstitial disease in Manitoba, and that is a good thing.