key: cord-0817434-vfrtzppb authors: Hamilton, N. E.; Adam, G. H.; Ifan, D. L.; Lam, S. S.; Johnson, K.; Vedwan, K.A.G.; Shambrook, J. S.; Peebles, C. R.; Harden, S. P.; Abbas, A. title: Diagnostic utility of additional whole-chest CT as part of an acute abdominal pain CT imaging pathway during the COVID-19 pandemic date: 2020-06-09 journal: Clin Radiol DOI: 10.1016/j.crad.2020.06.002 sha: 41efef6f8455265d8da4a5e6d39d2b8d969b9946 doc_id: 817434 cord_uid: vfrtzppb Abstract Aim To evaluate the diagnostic utility of additional whole-chest computed tomography (CT) in identifying otherwise unheralded COVID-19 lung disease as part of an acute abdominal pain CT imaging pathway in response to the COVID-19 pandemic. MATERIALS AND METHODS Consecutive patients (n=172) who underwent additional whole-chest CT via a COVID-19 acute abdominal pain CT imaging pathway between 27 March and 3 May 2020 were evaluated in this retrospective single-centre study. Chest CT examinations were graded as non-COVID-19, indeterminate for, or classic/probable for COVID-19. CT examinations in the latter two categories were further divided into one of three anatomical distributions (lung base, limited chest [below carina], whole chest [above carina]) based on location of findings. Reverse transcriptase-polymerase chain reaction (RT-PCR) results and clinical features of COVID-19 were assessed to determine if COVID-19 was clinically suspected at the time of CT referral. RESULTS Twenty-seven of the 172 (15.7%) patients had CT features potentially indicative of COVID-19 pneumonia, 6/27 (3.5%) demonstrating a classic/probable pattern and 21/27 (12.2%) demonstrating an indeterminate pattern. After correlation with clinical features and RT-PCR 8/172 (4.7%) were defined as COVID-19 positive, of which only 1/172 (0.6%) was clinically unsuspected of COVID-19 at the time of CT referral. All COVID-19 positive cases could be identified on review of the lung base alone. CONCLUSION Whole-chest CT as part of an acute abdominal pain CT imaging pathway has a very low diagnostic yield for the present cohort of patients. All COVID-19-positive patients in the present cohort were identified on review of the lung bases on the abdominal CT and this offers an alternative imaging approach in this patient group. In December 2019, China reported a cluster of pneumonia cases in Wuhan, which was later discovered to be caused by SARS coronavirus 2 (SARS-CoV-2) and was given the name COVID-19. COVID-19 spread rapidly around the globe and on 11 March 2020, the World Health Organization (WHO) declared a global pandemic. To date, there have been over 4 million cases worldwide, with over 215,000 confirmed cases and over 31,000 deaths in the UK alone [1, 2] After exposure to the virus, there is an asymptomatic incubation period lasting on average 5-6 days, but this can be up to 14 days [3] . Fever, dry cough, and myalgia are the most frequently occurring symptoms [4] . Among atypical COVID-19 presentations, gastrointestinal symptoms including abdominal pain, diarrhoea, and nausea have been reported [5] . The typical imaging characteristics of COVID-19 have been well documented in the literature. Chest radiography demonstrates bilateral, peripheral pulmonary infiltrates, and on thoracic computed tomography (CT), the most common appearance is multifocal, subpleural, ground-glass opacification with a basal predominance. Interlobular septal thickening and consolidation are also commonly present [6, 7] . In March 2020, the Lancet published a Chinese study by Lei et al. [8] demonstrating poor post-surgical outcomes in 34 COVID-19 positive patients who had undergone planned surgery during their incubation period. Concerns regarding reported increased intensive care unit (ICU) admission and mortality rates in this study prompted some surgical societies to issue guidelines on preoperative patient care. In the UK, this included the Intercollegiate General Surgical Guidance on COVID-19, which recommended all patients presenting acutely or requiring emergency surgery and undergoing CT of the abdomen and pelvis, should also undergo CT of the whole thorax [9] . This was supported by the Royal College of Radiologists and incorporated into the British Society of Thoracic Imaging (BSTI) and British Society of Gastrointestinal and Abdominal Radiology (BSGAR) decision tool for chest imaging in patients undergoing CT for acute abdominal pain [10, 11] . The rationale proposed for justifying additional imaging in this cohort of patients is that the chest CT findings, in conjunction with a low probability of COVID-19, might assist the surgical decision to pursue conservative or operative patient management. To date, there has been no published data to assess the role of whole-chest CT as part of an acute abdominal pain imaging pathway to identify otherwise unheralded COVID-19 lung disease. Furthermore, review of the literature reveals variation in the sensitivity of thoracic CT in COVID-19 positive patients during the incubation period. The study by Inui et al. had the largest sample size (76 asymptomatic patients) and reported 54% sensitivity [12] . Smaller studies with sample sizes ranging from three to 26 patients demonstrated higher sensitivities from 65-71% [13] [14] [15] . The UK has reportedly now passed the peak of the first wave of coronavirus cases. The post-peak phase may potentially last for 6-18 months [16, 17] and is predicted to be characterised by declining disease prevalence and public health efforts to prevent future peaks. It is therefore necessary to re-assess and rationalise imaging pathways put in place earlier in the pandemic to ensure they remain appropriate and sustainable. This is especially important as elective imaging, and consequently radiology departmental activity, begins to return to pre-pandemic levels. The principal aim of this retrospective study is to evaluate the diagnostic utility of additional whole-chest CT in identifying otherwise unheralded COVID-19 lung disease as part of an acute abdominal pain imaging pathway in response to the COVID-19 pandemic. The secondary aim is to evaluate potential alternative CT approaches for this cohort of patients. This retrospective study was assessed by the Health Research Authority and local research and development Committee as not requiring ethics approval and written informed consent was waived for all cases. Inclusion criteria for this retrospective study were defined as patients who had presented to our institution between 27 March to 3 May 2020 as an emergency with acute abdominal pain and, subsequently, undergone CT chest, abdomen, and pelvis according to the Intercollegiate General Surgical Guidance, RCR guidance and BSTI/BSGAR decision tool [9, 10] . Patients were identified as suitable for inclusion Continuous data were represented using the mean and standard deviation (SD) whilst categorical variable were represented using percentages. Table 3) . All cases with a classic/probable pattern of COVID-19 pneumonia on CT (n=6) were visible at the lung bases, meaning the diagnosis could have been confirmed without an additional CT (Table 4) . Those with indeterminate CT findings (n=21) were visible at the lung bases in 66.7% of cases and below the carina in 90% of cases. Of note, in the two cases with indeterminate CT features defined as COVID-19 positive after clinical and RT-PCR correlation, the CT findings were visible at the lung bases. Clinical suspicion for COVID-19 at the time of referral for CT In total, 7/27 patients (26%) with CT appearances graded as either indeterminate or classic/probable for COVID-19 were suspected clinically as having COVID-19 at the time of referral for CT (Table 3 ). In 20/27 (74%) patients in whom COVID-19 was not suspected clinically at the time of referral for CT, only a single case was identified as being COVID-19 positive after CT. This equates to a total unheralded COVID-19 lung disease diagnostic rate in the present cohort of patients of 1/172 (0.6%). In this single case, the abnormality on CT was present at the lung bases. The mean additional DLP associated with performing the thoracic CT was 266.7 (± 218.9) mGycm (Table 5 ). This resulted in an estimated mean increased radiation dose of 3.7 (±3.1) mSv (Fig. 4) . During the transition into the next phase of the COVID-19 pandemic, it is vital that the longer-term suitability of imaging pathways established to support patient care during the initial surge phase of this global public health crisis is reviewed [9] [10] [11] . Although the numbers of cases in the UK continues to fall [16] , it is anticipated that SARS-CoV-2 will remain prevalent in society for many months until a suitable vaccine is available for widespread use [6] . In this context, it is essential pragmatic precautionary measures are developed that safeguard the health of communities and healthcare workers, whilst at the same time ensuring that these practices are sustainable in order to enable radiology departments to restore elective activity to pre-pandemic levels. The role of whole-chest CT to screen for COVID-19 lung disease in asymptomatic groups remains controversial. Although major UK and international imaging societies do not support the routine use of CT for screening for COVID-19 lung disease, some potential exceptions have been proposed for selected groups. This includes patients with acute abdominal pain and those undergoing certain types of elective surgery requiring postoperative ICU care [9] [10] [11] 18] . The rationale for supporting the use of whole-chest CT is based on isolated reports of unheralded COVID-19 infection in patients presenting with acute abdominal pain as well as reported poorer postoperative outcomes in patients with COVID-19 disease [8, 10] ; however, there are few data in the literature to evaluate the diagnostic utility of imaging pathways incorporating whole-chest CT to address this issue, or that the introduction of these pathways significantly alters clinical outcomes [8, 20] . Some authors have recommended that alternative approaches to whole-chest CT in these settings should be formally evaluated, including the role of review of limited lung CT images acquired for abdominal pain and other non-thoracic clinical indications prior to patient transfer from the CT machine [20, 21] . Our institution is a large tertiary referral centre in the UK with 1,400 hospital beds, providing care for a local catchment area of 0.5 million people and a tertiary referral population of approximately 3 million people. The BSTI/BSGAR additional wholechest CT for acute abdominal pain COVID-19 imaging pathway was introduced 28 March 2020 as part of the institution's evolving response to the initial surge phase of the COVID-19 pandemic [10, 11] . Retrospective review of the institution's experience with this pathway was performed as part of an ongoing decision-making process for restoration of elective imaging levels within the department. Similar activity will undoubtedly be performed within other radiology departments in the UK. Where appropriate, it is vital that these experiences are disseminated widely to guide the ongoing efforts of the radiology community to develop practical and safe workflow solutions for healthcare delivery until effective widespread SARS-CoV-2 vaccines are available. In the present cohort of acute abdominal pain patients, only six (3.4%) had classic/probable CT findings of COVID-19 and only a further two (1.1%) cases with indeterminate CT findings of COVID-19 were confirmed to be COVID-19 positive following correlation with clinical and RT-PCR findings. The total diagnostic yield for COVID-19 lung disease in the present study was eight (4.6%) and only one (0.6%) of these cases was clinically unsuspected for COVID-19 at the time of CT referral. Overall, this represents a very low diagnostic yield for unheralded COVID-19 lung disease. The additional whole-chest CT performed as part of this pathway resulted in the present patients receiving a mean additional radiation dose of 3.7 mSv (DLP 266.7). Many authors have questioned the need for CT assessment in patients who are clinically stable and RT-PCR positive, as CT findings would not alter clinical diagnosis or management in these cases [19, 22] . In patients who are RT-PCR negative, the role of CT is less well defined, but assessment of asymptomatic patients can result in significant false-negative rates of up to 46% [12, 22] . Based on the authors' experience, additional whole-chest CT as part of a COVID-19 acute abdominal pain pathway has a very low overall diagnostic yield, and it is, therefore, difficult to continue to justify the increase in radiation dose that these patients are exposed to. In total 27 (15.7%) of the present cohort demonstrated abnormalities on CT, which were either classic/probable, or indeterminate for, COVID-19. Of these 27 cases, 74% were identifiable at the immediate lung bases and 90% within the lung below the carina. All eight patients (100%) with confirmed COVID-19 disease had abnormalities that could be identified at the lung bases alone. Specifically, the single case of unheralded COVID-19 in the patient cohort would have been diagnosed on review of the lung bases only, potentially negating the need for whole-chest CT in this group of patients. Although the detailed distribution of lung abnormalities comparing lung bases to limited lower lobes below the carina has to the authors' knowledge not been reported, the prevalence of lower-lobe abnormalities identified on CT in patients with COVID-19 is reported to be as high as 93-98% in both Asian and European populations [23, 24] . Unfortunately, the relatively small number of COVID-19 positive patients in the present cohort makes it difficult from the present data alone to make definitive recommendations on the use of a lung base review versus a limited chest review strategy; however, when combined with the known very high prevalence of lower-lobe disease, this would support the use of at least a limited lower-lobe imaging assessment for acute abdominal pain rather than necessitating a wholechest CT approach, particularly for patient populations with a relatively low COVID-19 prevalence [23, 24] . Further assessment of established COVID-19 CT imaging databases to define the distribution of lung parenchymal abnormalities in patients with confirmed COVID-19 lung disease using a lung base versus limited lungs (below carina) versus whole-chest scoring system is recommended to better define the relative roles of these CT strategies for acute abdominal pain patients [25] . Several limitations of the present study should be addressed. In the setting, clinical, demographic and outcome data were limited due to the retrospective study design and the timeframe allowed for analysis, in the context of an urgent need to provide evidence to guide decision-making around this imaging pathway at a time when greater levels of elective imaging care are required locally and across the UK. One limitation in particular, was that not all of the present patients had RT-PCR testing if not clinically considered to be COVID-19 positive as was standard practice at that time. Although this means some of the indeterminate CT patients only had clinical correlation with CT findings to establish their COVID-19 clinical status, the fact that RT-PCR testing was not performed in these patients is likely to indicate that there was no significant clinical suspicion of COVID disease in this subgroup. The present study is further limited by retrospective analysis of data from only a single centre, which reflects the prevalence of SARS-CoV-2 in the present cohort. This potentially means the present experience will differ from other centres with different COVID-19 disease burdens. In particular, those centres with a significantly higher prevalence of COVID-19 infection may experience a greater diagnostic yield than was seen in the present cohort due to higher burden of disease in the population of patients attending their institutions' emergency departments. Although this was a particularly important consideration during the initial surge phase of the pandemic, geographic differences in disease prevalence in the UK is anticipated to change as overall disease burdens decrease based on the experience of other countries [16] . In conclusion, the present single-centre study suggests that the use of additional whole-chest CT in patients referred for CT assessment of acute abdominal pain has a very low diagnostic yield for identifying unheralded COVID-19 lung disease. In the present institution, these findings also support review of the limited lung base images rather than necessitating a whole-chest CT for all patients with acute abdominal pain. This approach warrants further multicentre evaluation but may be applicable more widely. Values are mean ± SD or n (%). CT, computed tomography; RT-PCR, reverse transcriptase-polymerase chain reaction. Values are n (%). CT, computed tomography; RT-PCR, reverse transcriptase-polymerase chain reaction. CT, computed tomography. Values are n (%). CT, computed tomography. Values are mean ± SD. a Fourteen patients excluded as CT chest performed as a continuous helical scan with the abdomen and pelvis. European Centre for Disease Prevention and Control. 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