Chest computed tomography of patients having coronavirus disease (COVID-19) will be analyzed with regards to vascular abnormalities (pulmonary embolism and vascular thickening), and their association with lung inflammation. The prevalence, severity, distribution, and prognostic value of chest CT findings will be assessed. Patients with vascular abnormalities will be compared to patients without, which is supposed to provide insights into the prognostic role of such abnormalities, and the potential impact on treatment strategy.

Since the SARS-CoV-2 outbreak, computed tomography (CT) imaging has almost immediately established itself as the primary non-invasive diagnostic tool for diagnosis, monitoring of COVID-19 pneumonia, and complications thereof.

While most of the currently available literature relies on non-contrast CT, the need to assess vascular abnormalities is being recognized as an increasingly important factor, both to help distinguish COVID-19 pneumonia from other viral infections, and to exclude pulmonary embolism (PE). Acute PE is believed to be a significant contributory factor in patients with adverse outcomes.

Relating to vascular changes other than PE, additional knowledge is required and not yet available to confirm and better understand early observations. In particular, a radiological sign referred to as "vascular thickening", "vascular enlargement", or "vascular congestion" that is thought to be a specific marker of COVID-19 pneumonia, calls for a thorough assessment. Quantitative analysis of this sign and correlation to clinical presentation is highly desirable.

The investigators will conduct a multicentric observational study in the form of a registry. For this purpose, each participating center needs to screen hundreds of COVID-19 patients to select those who meet the inclusion criteria and do not have any exclusion criteria. Then, clinical, laboratory and imaging data of eligible patients will be retrieved. The research will focus on the imaging manifestations of COVID-19 pneumonia and their relationship to vascular abnormalities within the lung; the potential association between such vascular abnormalities and COVID-19 clinical severity will be assessed.

To achieve adequate statistical power, the study needs to be multicentric, involving 7 Swiss institutions; CHUV Lausanne, USZ Zurich, USB Basel, Inselspital Bern, Division Stadt- und Landspitäler Inselgruppe, HUG Genève, HRC Rennaz. The following investigators are involved in this extensive nationwide effort:

• CHUV: Dr DC Rotzinger; Prof SD Qanadli; Prof PY Bochud; Prof L Alberio; Dr JL Pagani
• USZ: Prof H Alkadhi
• USB: Prof J Bremerich; Dr A Sauter
• Inselspital: Prof T Heverhagen; Prof L Ebner
• Division Stadt- und Landspitäler Inselgruppe: Prof A Christe
• HUG: Prof A Poletti
• HRC: Prof O Ratib

Intrahospital medical records, laboratory tests results, and data from chest CT performed in the participating centers between March 1st and July 31st, 2020 will be used to:

• assess the frequency of non-PE related vascular abnormalities on chest CT (vascular thickening), and their association with parenchymal opacities
• evaluate the rate of acute PE among the patients undergoing contrast-enhanced chest CT
• quantify the clot burden in terms of proximal or distal obstruction and quantitative CT obstruction index (CTOI) in patients with CT-proven PE
• evaluate the consequence of PE on pulmonary perfusion (distinguishing perfused vs. non-perfused pulmonary opacities) and cardiac morphology (right ventricle dilatation, reduced left atrial size)
• evaluate the correlation between pulmonary perfusion impairment and clinical severity

Using clinical, laboratory and CT imaging-derived variables, the investigators will perform outcome modelling to derive an integrative score to predict outcomes.

Inclusion Criteria:

• Patients admitted for COVID-19 (with positive rt-PCR for SARS-CoV-2) who had a contrast-enhanced chest CT within the specified timeframe.

Exclusion Criteria:

• Age <18 years Patients with another pre-existing infectious process Documented refusal of the reuse of medical data

All patients with positive rt-PCR for SARS-CoV-2 and chest CT (with or without intravenous contrast material injection) within the specified time frame.