Pulmonary Thrombosis (PT) in Patients with Covid-19 Pneumonia: is It Pulmonary Thromboembolism or Thrombosis in Situ?

Introduction Mechanisms of PT in COVID-19 are unknown. Thromboembolism and local pulmonary inflammation are suggested as potential factors, but most data come from retrospective studies with patients included due to clinical suspicion, and association between number of thrombi (NT) and pulmonary involvement (TLI) has not been evaluated yet. Objectives (1) To determine the NT surrounded by lung opacification (TSO), their percentage (PTSO) in each COVID-19 patient, and the relationship with TLI. (2) To analyze the PTSO, according to location and TLI. Methods Seventy consecutive patients admitted to the hospital with COVID-19 pneumonia and PT were included. All computed tomography pulmonary angiographies were analyzed at patient level (TLI and PTSO/patient), and at thrombi level (NT, TSO and PTSO). A random thrombus location would correspond to a PTSO equivalent to TLI. Results Three (2-8) thrombi/patient were detected, with PTSO/patient of 100% (75-100%). Sixty-five patients (92.9%) were above the random scenario and had significantly more PTSO/patient than TLI independent of TLI. Most thrombi (n=299, 75.1%) were TSO. TLI was higher in TSO compared to non-TSO (20.5 vs. 2.2%), but when evaluating by TLI (<10, 10-20, 20-30, and >30%), PTSO was higher in most groups. Thrombi were mainly in subsegmental/segmental arteries, and PTSO was significantly higher in all locations. Conclusions COVID-19 patients had higher PTSO than TLI. Most of the thrombi were TSO, independently of TLI, and its location, supporting the hypothesis that COVID-19 could promote local pro-thrombotic phenomena rather than classic thrombo-embolism.