DISCUSSION:
In our study, we aimed to expose the radiologists’ increasing experience on evaluation of chest-CT findings of COVID-19 pneumonia. We have focused on some unobserved challenges on radiologists’ in the COVID-19 pandemic to better understand the diagnostic differences in re-evaluation.
Correlation of re-evaluated chest CT results with PCR tests have demonstrated that PCR test was negative in 84.1% of the scans in “not covid” group. On the other hand, the 91.7% PCR-positivity were calculated in the cases labelled for “normal”. This finding can be explained with the vigorous use of CT in the ER setting, even for the patients who has COVID-19 infection but lack of pneumonia. Calculations with “typical for covid”, “atypical for covid” and combination of this two groups have resulted in 62.8% sensitivity and 40% specificity of Chest-CT according to PCR test results.
We have identified diagnostic differences in 18.5% of the chest CT scans in our cohort. The distribution of this EIs have shown a dramatic accumulation within the first 60 days of pandemic in our country. After this point, the of IEs decrease down to 11.18% (figure 2). There are some reasons that can explain the possible causes of this relatively high EI ratios and its course among the first three months of pandemic. First of all, both national and global total number of cases and new confirmed cases prominently increased within the first two months. The number of total cases significantly increase from ~116.000 to ~3.2 million with an increase in new confirmed case from 4600 to 86.000/day worldwide. Similarly, a total of ~120.000 cases have been identified in our country between 10th March and 1stMay, 2020 with a 2615/day new confirmed cases on 1stMay (5). Our institution as well as most of the healthcare centres worldwide have faced striking hospital admission rates up to ~1000/day with the spread of coronavirus. Between 1st of May and 1st of June, new confirmed daily cases decrease by 67.92%. As of 8thof January 2021, the cumulative number of covid cases are nearly 1.5 million in our country (5). We have re-evaluated the study cohort with a remarkable experience of ~17.000 chest CT scans reported in the past 9 months at our institution.
During pandemic, workload of radiologists have expeditiously increased parallel to the admissions with the suspicion of COVID-19. According to the COVID-19 guidelines published by the ministry of health (appendix-2), chest CT scanning have become the secondary diagnostic tool after the gold standard PCR testing. To overcome the delay in diagnosis due to the PCR testing, clinicians encouraged to use the CT scan as the quickest way to isolate/hospitalize the COVID-19 infected patients (7). Moreover, Chest-CT gained an important role in clarification of PCR-false negative but clinically highly suspected cases.(8) These all have seem to be contributed to acquisition of 5721 Chest CT-scans within this three month period. For comparison, there were approximately 900 chest CTs performed at out institution between the same months of the last year (March to June, 2019). Radiologists on shifts were directly affected from this six-fold increase; up to a total of 140 covid-suspected chest CT scans were reported in a day, along with the other non-covid emergencies. Reporting time was approximately 10-30 minutes after the acquisition. Another difficulty was that the covid dedicated CT scanning protocol included approximately 320 axial slices with a 1 mm slice thickness which makes it more time consuming than the standard chest CT scanning protocol with 3-5 mm slice thickness. All in all, exponentially increased admission rates along with the increased number of covid dedicated, thin slice chest CT scans have become grounds for possible interpretation errors.
Another point worth mentioning is that; although most typical signs of covid pneumonia on chest CT had first identified in Wuhan-China, numerous atypical signs had evolved with the spread of the infection to different profile of patients. As Falaschi et al . stated, incorporation of China experience along with the other previously contaminated countries into daily clinical practice seems to have caused an improvement in our diagnostic accuracy (4). The recognition of the relationship between atypical findings for COVID-19 pneumonia on Chest CT may have contributed to the decline of IE rate. Another possible contributor is the aggregation of educational activities focused on radiological findings of covid pneumonia in the first two months.
Further analysis have shown a marked uneven distribution of IEs among the four CT result groups. More than half of the errors have been made in the “not covid”, followed by the “atypical for covid” group. IEs in the re-evaluated “not covid” group were mostly consisted of incorrect diagnosis for “atypical for covid”. Similarly, analysis of re-evaluated “atypical covid” group have shown a marked incorrect diagnosis for “typical for covid”. These findings have shown us that that the radiological hallmarks of covid pneumonia were successfully identified but there were lack of experience and knowledge, specifically about atypical radiological findings. This situation had probably created a tendency to not to exclude the covid diagnosis, yet point out a suspicion with the statement of “atypical for covid” in CT reports. Another issue to mention is that, there are subspecialized academic and staff radiologists at our department. The COVID-19 pandemic have necessitated rapid responses from radiology departments to overcome the increased demand on diagnosis and management of covid pneumonia. Along with the partial cancellation of elective diagnostic/interventional procedures and outpatient diagnostic services; nearly all radiologists were integrated into a team dedicated to COVID-19 diagnosis. Therefore, as Vijayasarathi et al . stated, subspecialised radiologists have faced an unexpected challenge in this crisis to maintain their versatility in reporting chest CT scans (9). Similarly, Shi et al. and Cavallo et al. have also mentioned imperative outside-role definition of radiology employees (10,11). Hereby, this situation might also contribute to the escalation of interpretation errors. Considering together with the increased workload and physical and psychological stress of pandemic, it seems nearly inevitable to make interpretation errors in the COVID-19 outbreak.
There are some limitations this study. First, we could have included only 13.6% of the Chest CT scans due to lack or delay of PCR test results. Second, we have ignored decline in non-COVID CT cases per/day and focused on COVID dedicated CT reporting volume.
There’s no doubt that COVID pandemic made a huge impact on radiology practices worldwide. Increment of covid-related admission rates and relevant increase in daily workload, rotations of subspecialized personnel for urgent health care management along with growing diagnostic experience over time have possible effects on radiology departments’ performance.