Reticular pattern was defined as thickened pulmonary interstitial structures such as interlobular septa and intralobular lines [26, 29], manifested as a collection of innumerable small linear opacities on CT images (Fig. 2a). The formation of this pattern might associate with interstitial lymphocyte infiltration causing interlobular septal thickening [27]. Several studies have listed reticular pattern with interlobular septal thickening as the common chest CT manifestation of COVID-19, only second to GGO and consolidation [15, 18, 19]. As the disease course gets longer, the prevalence of reticular pattern could increase in COVID-19 patients [18].
Fig. 2 a A 34-year-old female COVID-19 patient presenting fever with dry cough for 2 days. CT scan shows slight reticular pattern in the left lower lobe and subpleural area (red frame). b An 81-year-old female COVID-19 patient presenting fever with cough for 7 days. CT scan shows reticular pattern superimposed on the background of GGO, resembling the sign of crazy paving stones in the right middle lobe (red frame)