FIGURE 1.

a) Axial chest computed tomography scan showing a full-thickness tracheal lesion with fistula. b) Tracheal cartilage micro-cracks in a patient with coronavirus disease 2019 (COVID-19) and pneumomediastinum (Haematoxylin and eosin ×40). c) Basophilic cartilage matrix and intracellular fracture with chondrocyte apoptosis (Haematoxylin and eosin ×20). d) Control non-COVID-acute respiratory distress syndrome with absent Sonic Hedgehog (Immunohistochemistry ×20). e) Weak positive Sonic Hedgehog tracheal chondrocytes in a COVID-19 patient (Immunohistochemistry ×20). f) Strong expression of Wnt5a in the same patient (Immunohistochemistry ×20).