Objectives Diagnostic tests for SARS-CoV-2 are important for epidemiology, clinical management, and infection control. Limitations of oro-nasopharyngeal real-time PCR sensitivity have been described based on comparisons of single tests with repeated sampling. We assessed SARS-CoV-2 PCR clinical sensitivity using a clinical and radiological reference standard. Methods Between March-May 2020, 2060 patients underwent thoracic imaging and SARS-CoV-2 PCR testing. Imaging was independently double- or triple-reported (if discordance) by blinded radiologists according to radiological criteria for COVID-19. We excluded asymptomatic patients and those with alternative diagnoses that could explain imaging findings. Associations with PCR-positivity were assessed with binomial logistic regression. Results 901 patients had possible/probable imaging features and clinical symptoms of COVID-19 and 429 patients met the clinical and radiological reference case definition. SARS-CoV-2 PCR sensitivity was 68% (95% confidence interval 64-73), was highest 7-8 days after symptom onset (78% (68-88)) and was lower among current smokers (adjusted odds ratio 0.23 (0.12-0.42) p<0.001). Conclusions In patients with clinical and imaging features of COVID-19, PCR test sensitivity was 68%, and was lower among smokers; a finding that could explain observations of lower disease incidence and that warrants further validation. PCR tests should be interpreted considering imaging, symptom duration and smoking status.

Colorectal cancer is the third most commonly diagnosed cancer in men and second most commonly diagnosed cancer in women worldwide. Initial diagnosis of colorectal malignancy is generally made on colonoscopy, sigmoidoscopy or digital rectal examination; however, with increased use of CT as primary investigation in patients with lower gastrointestinal symptoms, the diagnosis of colon cancer is often first apparent to a radiologist prior to more invasive tests. CT can demonstrate a discrete soft-tissue mass that narrows the colonic lumen or focal nodular wall thickening/stricture and a variety of pericolonic changes. Pattern of wall thickening has been described as an aid to differential diagnosis; however, significant overlap remains between primary colonic tumor and non-colonic tumors or benign conditions. Imaging is non-specific, and appropriate clinical history, direct inspection, histological analysis, and sometimes discussion at MDT are essential for accurate diagnosis and treatment planning. In this article, we will review the imaging features of some of these benign and malignant mimics of colorectal cancer, with accompanying histology slides where appropriate.

339 Background: Patients with muscle invasive bladder cancer receiving neo-adjuvant chemotherapy (NAC) prior to radical cystectomy or organ preservation treatment are at higher risk of thrombo-embolic events (TEE). Methods: Retrospective data were collected on patients undergoing NAC prior to radical treatment who had surveillance CT scan chest abdomen pelvis following NAC to assess for response or underwent scan following clinical presentation during NAC requiring imaging. The aim of this study was to document the incidence and characteristics of TEE during NAC prior to radical treatment. Results: Data were collected on 94 patients between January 2012 and December 2015. Median patient age was 67 (IQR: 63, 72) with 28 (30%) females. Chemotherapy received was Cisplatin and Gemcitabine in 90% of cases, Gemcitabine and Carboplatin (9%), and Cisplatin and Etoposide (1%). Performance status was 0 in 59% of cases. G3 disease was recorded in 87%, T2 or T3 in 80% and TCC in 91% of cases. 28 TEE (29.8%, 95 % CI: 20.5%, 39%) were recorded of which 22 (79%) were subclinical TEE and 6 (21%) were clinical TEE. 23 (82%) of TEE were pulmonary emboli, 2 (7%) were concurrent pulmonary emboli and deep vein thombosis, 2 (7%) were abdominal aorta thrombosis, and 1 (4%) was a deep vein thrombosis. Conclusions: Our single centre study demonstrates that the incidence of TEE during NAC prior to radical treatment for bladder cancer is high. Improved imaging techniques lead to reporting of number of sub clinical TEE of uncertain clinical significance. These findings give weight to future prospective clinical trials to investigate the role of anti-coagulation in subclinical TEE and benefit of prophylactic anti-coagulation during NAC.

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