Dr Abhishek Neral

Dr Abhishek Neral is the Director and Consultant Radiologist at Galaxy Vidarbha Diagnostic at Nagpur. He has completed Masters in Radio Diagnosis (MD) and has worked at various reputed hospitals including Guys & St.Thomas (London, UK), Conquest Hospital (Hastings UK), SMC Medical Center (Dubai), Breach Candy Hospital Trust (Mumbai) to name a few.

High Resolution Computed Tomography also known as HRCT or CT scan is a fast emerging tool now being widely used for better analysis of the lungs and COVID-19 among patients.

Why do we need HRCT scan for diagnosis of COVID-19?

COVID₹19 is a respiratory system illness that manifests as upper respiratory tract infection, which settles downs with pneumonia, consolidation, pulmonary infractions and eventually lung fibrosis.

In response to viral attack, the body tries to fight back by liberating various protective enzymes, which evolve inflammatory reaction. When body tries to counteract replicating viral load, it releases lots of Cytokinin called as cytokine storm as an immune response.

If the body fails to counteract this viral attack, it leads to multi-organ failure and eventually morbidity and mortality. To prevent these complications early diagnosis and treatment is the key.

Given today’s scenario, the count of COVID₹19 cases is increasing at an unstoppable rate. Maharashtra is experiencing increasing number of cases by the day.

However there is no guarantee that the cases that are being reported are the same as actual number of COVID cases amongst the public. The major reason behind this fall back is the problem we are facing with the testing of COVID.

Diagnosis is usually made with an RTPCR assay, also known as the SWAB test.

However, the RTPCR itself has limitations:

False negative results can occur because of incorrect sampling, location of the swab test, insufficient viral material in the specimen and test sample quality.

The sensitivity of this test is considered as low as 59%₹71%, more importantly the shortage of test kits.

Also, RT-PCR takes hours or even days before the results are available. Such limitations and delays would lead to increase and transmission of infection. Due to these inaccuracies, dependency on RT-PCR cannot be continued for quick and accurate test results of the patients and hence treatment and recoveries.

How can HRCT san compensate for the above limitations

HRCT examinations, however, can compensate for the above limitations. HRCT scans can play a very important role in the diagnosis and management of COVID-19 patients. HRCT scan is more accurate (95% according to the recent reports).

It decreases the chances of false-negative results. Many suspected patients with atypical CT findings but a negative RT-PCR test have been found to have this disease. HRCT scan process is relatively simple and quick and can be used as a rapid screening tool for suspected patients when RT-PCR results are negative and results are available right away.

This leads to early detection and early isolation and prevents transmission of the virus.

HRCT findings are positive for viral pneumonia sometimes even before laboratory results are positive or in false-negative reports.

A predictive model and scoring system combining both clinical and CT features are developed to enable high diagnostic efficiency for COVID-19.

Therefore, chest CT findings in particular high resolution computed tomography (HRCT), represents a valuable tool to identify patients with COVID-19 infection in early stage when clinical symptoms may be nonspecific or sparse.

CO-RADS CLASSIFICATION
The COVID-19 Reporting and Data System (CO-RADS) developed by the Dutch Radiological Society, (approved by ICMR) provides a framework for reporting HRCT.

Clinicians for ease of communication and workflow optimisation readily embraced CO-RADS. It assesses the suspicion for pulmonary involvement on CT. Based on the CT findings, the level of suspicion of COVID-19 infection is graded from very low or CO-RADS 1 up to very high or CO-RADS 5 and hence the severity and stage of the disease is determined.

CT involvement score known as the CT severity score (CTSS)
The severity of the lung involvement on the CT correlates with the severity of the disease. The method is by scoring the percentages of each of the five lobes that are involved. The total CT score is the sum of the individual lobar scores and can range from 0 (no involvement) to 25 (maximum involvement). There is another system to calculate with segmental involvement of count 40. Typical CT manifestations of COVID-19 have been described including Ground glass opacity (GGO), crazy-paving pattern, and multifocal lesions in a peripheral distribution.

GGO and consolidation are two main signs of COVID-19 lesions on CT images.

Conclusion

HRCT is an important investigation for diagnosis, grading, severity and prognosis of the disease. Positive results can determine whether patient needs immediate hospitalisation or not. Follow up study reveals progression or resolution of disease.

HRCT displays various lung patterns in COVID-19 positive cases. HRCT is necessary for accurate diagnosis; scan procedure is simple and sensitivity is as high as 95%. Moreover, reports and results are available right away.

HTCT can also be used as a follow-up tool to monitor the evolution and severity of the virus in the patients. It is perhaps a great tool for management and patient care considering the on-going scenario.

(Views are personal)