In this retrospective study, chest CTs of 121 symptomatic patients infected with coronavirus disease-19 (COVID-19) from four centers in China from January 18, 2020 to February 2, 2020 were reviewed for common CT findings in relationship to the time between symptom onset and the initial CT scan (i.e. early, 0-2 days (36 patients), intermediate 3-5 days (33 patients), late 6-12 days (25 patients)). The hallmarks of COVID-19 infection on imaging were bilateral and peripheral ground-glass and consolidative pulmonary opacities. Notably, 20/36 (56%) of early patients had a normal CT. With a longer time after the onset of symptoms, CT findings were more frequent, including consolidation, bilateral and peripheral disease, greater total lung involvement, linear opacities, “crazy-paving” pattern and the “reverse halo” sign. Bilateral lung involvement was observed in 10/36 early patients (28%), 25/33 intermediate patients (76%), and 22/25 late patients (88%).
An average of 3,605 new cases of COVID-19 have been reported per day since our preliminary research was published on February 4, 2020 . Just as clinicians are evaluating more suspected patients, radiologists are similarly interpreting more chest CTs in those suspected of infection. Chest CT is a vital component in the diagnostic algorithm for patients with suspected COVID-19 infection. Indeed, given the limited number of rRT-PCR kits in some centers and the possibility of false negative rRT-PCR results, the National Health Commission of the People’s Republic of China has encouraged diagnosis based on clinical and chest CT findings alone. In this study of 121 patients with confirmed Covid-19 infection, it is noteworthy that 20/36 (56%) of patients imaged 0-2 days (‘early’) after symptom onset had a normal CT with complete absence of ground-glass opacities and consolidation (as opposed to 3/33 [9%] of intermediate patients and 1/25 [4%] of late patients). Only one of these patients (who was in the early group) had an initially negative rRT-PCR result, suggesting that rRT-PCR is positive even in patients with normal chest CT. Chest CT therefore has limited sensitivity and negative predictive value early after symptom onset, and is thereby unlikely a reliable standalone tool to rule out COVID-19 infection.
Other findings of this work largely concur with early radiology investigative efforts insofar as this pattern of ground-glass and consolidative pulmonary opacities, often with a bilateral and peripheral lung distribution, is emerging as the chest CT hallmark of COVID-19 infection. This pattern of disease, somewhat similar to that described in earlier coronavirus outbreaks such as SARS and MERS, also dovetails with the blueprint thoracic radiologists recognize as the archetypal response to acute lung injury whereby an initial (often infectious or inflammatory) acute insult causes ground-glass opacities that may coalesce into dense consolidative lesions, and then progressively evolve and organize in often a more linear fashion with predilection for the lung periphery (and somewhat with a “crazy” paving pattern or emergence of a “reverse halo” sign). The findings in this study, which highlight the increased frequency of such findings as consolidation, bilateral disease, greater total lung involvement, linear opacities, a “crazy-paving” pattern, appearance of the “reverse halo” sign, and peripheral lung distribution in patients imaged with CT a longer time after symptomatology starts, represent the CT correlate for the underlying pathophysiology of the disease process as it organizes. Moreover, the notable absence of ancillary chest CT findings such as lymphadenopathy, pleural effusions, pulmonary nodules, and lung cavitation likewise are consistent with early case descriptions.
There are several limitations to our study. Firstly, some patients were unable to be included in the evaluation of infection time course because of incomplete clinical histories where the precise time of symptom onset was unknown. Furthermore, some patients may have received medical intervention once suspected or confirmed to have infection (perhaps antimicrobial therapy, fluid administration, or steroid therapy may affect chest CT findings), which was not accounted for in this work. In addition, there may have been a selection bias in these institutions in terms of which patients were imaged with CT. For instance, if more clinically ill patients were more likely to be imaged sooner or imaged at all, then this may have an impact on results (although the opposite effect was observed in this study whereby those with the most severe lung involvement had a longer time between symptom onset and CT scan).
Our investigative efforts have demonstrated that frequency of CT findings is related to infection time course. Our data largely concur with work by Pan et al that demonstrated preponderance of ground-glass abnormality in early disease, followed by development of crazy paving, and finally increasing consolidation later in the disease course. Meanwhile, the outbreak is at a stage of evolving from the acute to a more subacute phase in many patients. Recognizing imaging patterns based on infection time course is paramount for not only understanding the pathophysiology and natural history of infection, but also for helping to predict patient progression and potential complication development. Eventually, as infection duration in a large number of patients extends from the acute and subacute phases to either a completely healed outcome or to a chronic phase in patients over the coming several weeks and months, future investigators may evaluate imaging findings in chronic patients. Such work could evaluate if long-term complications absent in this study (such as pleural effusions, empyema, lymphadenopathy, and lung cavitation) potentially arise.
Reference & Source information: https://pubs.rsna.org/
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