Covid-19 which is caused by SARS-CoV-2 erupted for the first time in Wuhan city of China in Dec, 2019 [1] . This virus mainly affects the lungs, resulting in mild to severe pneumonia which took the lives of millions of people around the world. Coronavirus has different variants including the newly identified UK variant (B.1.1.7) in December 2020 [2] . Since then other new variants have also appeared in other locations around the world. In Pakistan it was first isolated in Feb 2021, which has caused severe pneumonia in comparison with the previous strain.

However the Real-time polymerase chain reaction (RT-PCR) is considered the gold standard for the diagnosis of COVID-19, there are some limitations to this lab test as well, which include, probability of false negativity [3] [4] , it is time-consuming and not readily available, as well as low sensitivity of about 60% - 71% [5] . HRCT (high-resolution CT) has a crucial role in the diagnosis of COVID-19 pneumonia with a sensitivity of up to 98% [6] , particularly in cases with negative PCR or asymptomatic patients. HRCT is also useful in the assessment of the degree of damage [7] and monitoring the progression of the disease process.

Despite a wide variety of HRCT findings of COVID-19 pneumonia including crazy paving pattern, reversible halo sign, reticular pattern, airway changes [8] [9] [10] , ground-glass opacity (GGO) with posterior and peripheral distribution [11] was found to be the hallmark. This is also confirmed by the recent study performed by Omar et al. [5] .

After a review of the role of imaging in COVID-19 in recent studies, our objective is to study the HRCT features of COVID-19 pneumonia.

This prospective study which includes 127 COVID-19 positive patients (age 18 - 80 years, both genders) was conducted at Radiology Department of Sir Ganga Ram Hospital, Lahore in 2021 after clearance of local ethical review board.

Confirmed patients with brief clinical history were referred to radiology department during a time period of March 15 to April 15, 2021 for taking HRCT. After taking informed consent from the patients or their attendants and excluding situations like the low quality of images irrespective of its reason, HRCT indications other than COVID-19 pneumonia and patients who do not want to participate in the study, HRCT chest images without IV contrast were obtained in supine position in end-inspiratory phase. The 4-slice TOSHIBA CT scan machine was used to take all images with 2 mm slice thickness using 120 KV and 300 mAs. Bone algorithm was used for reconstruction process. As CT machine was being used for COVID-19 patients. After each scan CT machine was disinfected with ethanol. Data is then transferred to the workstation for interpretation. All variables including continuous and discrete were described as medians/ranges, and counts/percentages respectively.

Considering the exclusion and inclusion criteria which were already mentioned in method section, totally 127 COVID-19 confirmed patients ranging age from 18 to 80 years with mean age of 52 ± 18 years, took part in this study. There were 74 male and 53 female patients with a male to female ratio of 1.2:1. Demographic and major clinical characteristic are stated in Table 1. All HRCTs were interpreted and various CT features in COVID-19 infection were assessed. The pattern of detected HRCT findings is described in Table 2 and shown in Figures 1-5. Ground-glass haze was seen in all patients (100%) as shown in Figures 1-5. 119 patients (93.7%) revealed bilateral lung involvement as shown in Figures 1-3 and Figure 5. Only one patient had unilateral involvement (0.78%) as shown in Figure 4. Postero-basal and peripheral subpleural distribution of ground-glass haze were observed in 121 (95.2%) and 115 (90.5%) patients respectively with subpleural predominance shown in Figure 1 and Figure 5. Multi-lobe involvement was present in 113 (88.9%) patients with basal predominance shown in Figure 2, Figure 3 and Figure 5. Upper lobe distribution, consolidation, air bronchogram, bronchiectasis, crazy paving pattern, pleural effusion and mediastinal lymphadenopathy were identified in 78 (61.4%), 104 (81.8%), 80 (63%), 46 (36.2%), 11 (8.6%), 127 (3.1%) and 19 (14.9%%) patients respectively. whereas septal thickening was

appreciated in less than 20% of patients. Only two patients had pulmonary nodules. Consolidation with air bronchogram is shown in Figure 1, however crazy paving is shown in Figure 2.

Commonly observed HRCT findings are shown image vise above.

However, lots of studies conducted to evaluate findings of COVID-19 pneumonia in HRCT chest so far, particularly in the last year. We wanted to perform a study as well, in order to evaluate findings of disease during the third wave of COVID-19 in our population in 2021. Among 127 confirmed cases, the most common feature in all patients was found to be ground-glass opacification. Most of the hazes were observed bilaterally with typical posterior and peripheral distribution. Other typical manifestations were included consolidation having air bronchogram, bronchiectasis and crazy paving. Less common features were pleural effusion and septal thickening. Pulmonary nodules also presented as atypical features.

In comparison with our study, research conducted by Zhu et al. reported that ground-glass opacification was appreciated in only 47% of patients [12] [13] . As well, we described that consolidation presented in 81.8% of patients, however Salehi et al. [14] who conducted research on 919 patients reported that only 31% of patients had consolidation and prevalence of Peripheral and bilateral involvement of lungs and ground-glass opacification were reported as of (95.2% vs 76%) and (100% vs 88%) respectively. Study done by Omer et al. [6] which is performed on 30 patients, showing that crazy paving as compared to our study was found in 13.3% of cases. Mediastinal lymphadenopathy was not a common finding in our study.

A study by Bai et al. reported that 59% confirmed patients had increased calibre of pulmonary vessels at subsegmental level [15] [16] . This unusual finding was also reported by Albarello et al. in only 2 patients [17] . However, we did not report any subsegmental pulmonary vessel dilatation in any of our patients. Although the inflammatory changes have been shown to be the cause of pulmonary vessel dilatation [18] , variable studies attribute hyperemia caused by COVID-19 as compared to other viral pulmonary diseases [19] [20] [21] .

Despite constant referral of COVID-19 confirmed patients, there were few limitations too, including small sample size, follow up and almost lack of pediatric cases as well as no histopathologic correlation.

HRCT chest plays an important role in the diagnosis of COVID-19 pneumonia initially and can help in the proper assessment of the severity of the infectious process. In our study, the ground-glass haze was found to be the most common findings in all patients. Most of the hazes were observed bilaterally with the typical posterior and peripheral subpleural distribution involving multiple lobes, predominantly basal. Consolidation associated with air bronchogram and bronchiectasis was also found commonly.

The authors declare no conflicts of interest regarding the publication of this paper.

Hayat, A.M. and Bhatti, S.K. (2021) High Resolution Computed Tomography Features of Third Wave of COVID-19 Pneumonia in Confirmed Cases. Advances in Computed Tomography, 10, 11-17. https://doi.org/10.4236/act.2021.102002