Chest imaging in COVID-19

Iain Au-Yong, Consultant Radiologist.

Objectives

Background –first wave

• Reflections from first wave

• Very little known prior to first wave, preliminary data from China (CT)

• Suggested that imaging could be used for diagnosis and triage

• CXR preferred in Italy.

• Reference:

• Ai T, Yang Z, Hou H, et al. Correlation of Chest CT and RT-PCR Testing in Coronavirus Disease 2019 (COVID-19) in China: A Report of 1014 Cases. Radiology 2020 Feb 26:200642

Diagnosis of COVID-19

• Principles:

• RT-PCR is the gold standard for diagnosis but can be false negative (2-29%)

• Not readily available during the first wave

• Role of imaging:

• Diagnosis, for triage and management

• CXR and CT are the main imaging modalities in use, US is not in widespread use.

• Chest imaging has limited sensitivity and specificity.

• It should therefore be used in conjunction with clinical suspicion and biochemical indices (such as lymphopenia)

• Prognostication

• Detection and management of complications (egthrombosis)

Technical considerations

CT

• Less availability

• Disinfection more complex, risks to staff

• Additional burden of radiation dose and contrast administration (AKI in COVID),

• More sensitive. Specificity an issue

• Complex interpretation.

• Alternative diagnoses more readily made (PE, heart failure)

CXR

• More availability

• Portable CXR more practical, disinfection more straightforward

• Less sensitive. Specificity an issue

• Interpretation more straightforward.

• Can provide prognostic information

Covid 19 NUHT Triage v 217.3.20Suspected Diagnosis of Covid based on symptoms

Dry cough, Fatigue, Myalgia, Fever, Dyspnoea

For Escalation?Based on premorbid function and comorbidities*

Discuss with Respiratory Service

CT Chest*

CT featuresPeripheral multifocal airspace opacities

-Ground glass shadowing-Consolidation

(Majority will have bilateral involvement)

ClearOr Pleural effusion/Pneumothorax

No

F22/QMC

Well- Home

Unwell- ED

QMC/Gen MedConsider second

swab

NCH/Resp/Covid ward

1st Viral PCR

*Escalation factors need definingEg not for escalation-Chronic lung diseaseChronic heart disease

Age criteria

Yes

+ve -ve

NCH/Resp/Covid ward

QMCEDCOVID-19ADULTFLOWPROCESS–2ndApril**SeeEDIU&inpatientpathwayoptionsbelowforfulldetailsofadmissionpathways

1. Anynewcoughinlast7days

OR2. Newfeverwithin7days

OR3. Ambulancetemperature>

37.7C?

Areanyofthefollowingpresent?

• Sneezing,Nasaldischargeorcongestion

• Hoarsenessorsorethroat

• Dyspnoea/SOBorwheezing

• Fatigue/Myalgia

• Delerium/sepsisunknownsource

• D&V–(HCOPpatients)

Immediatedischargepossible?1. Patientlookswell2. HR<1003. O2Sats>94%(Roomair)

(>88%inCOPD)4. Norespiratorydistress

GiveinformationleafletProvidedischargeadviceRecordObs&decisiononMEDWAY

NON-COVIDProcess“ResusinMAJORS”

(MU1-10)MT–MU1

PaedsMT–MU5MUPatients–MU11-20

Illness-GREEN

DoespatientneedHighDependencyCOVID?(RESUS)

• NEWS>8

• Sats<92%despiteHFO2orrespdistress

• Potentialfordeterioration

DotheyneedanAGP?• CardiacArrest

Adult-(MACU1)Paeds–(Paedstreatmentroom)

• IntubationnorCPAP/NIV

A–Transfertheatre/AICUifpossibleB-UTUBay11C-MACUbay1+9D–COVIDResuslastoptionorimminentarrest

TransfertoCOVIDwardNCH&callnursing

stafftohandover

TransferEDIU1or2(MACU/UTU)

completeCXR&swabASAP

POTENTIALCOVID-19

Canbede-escalatedasNON-COVID??

CXR?COVID

Safefordischargeatanystage

AdmitNon-

COVIDwardQMC

Consider

HCOPPathwayorPalliativecare

SpecialistcareneededatQMCsite?

(Surgery,MT,complexgastroetc.)

AdmitunderspecialityatQMC

insideroom

Home

Home

Aretheyforescalation?

NO

NO

YES

YES

YES

YES

YES

YES

YES

AdmitNon-COVIDward

QMC

YES

NO

NO

YES

NO

Likelyclinicalsyndrome,withlymphopenia&raisedCRP?

NO

NO

RingRespBATONphone

COVIDCTPA

NO YESNO

NEGATIVE POSITIVE

ACCEPTED

NOTACCEPTED

NO

CXR

• Sensitivity 56% specificity 60%. (London, April 2020)

• (Borakati et al)

• However these figures vary with prevalence.

• Hot reporting

• Vvvv. Incidental COVID.

Borakati et al, BMJ Open. 2020 Nov 6;10(11):e042946.

Diagnostic accuracy of X-ray versus CT in COVID-19: a propensity-matched database study

BSTI COVID-19 CXR Report Proforma

Findings

Normal

COVID-19 not excluded. Correlated with RT-PCR

Classic/Probable COVID-19

Lower lobe and peripheral predominant multiple opacities that are bilateral (>> unilateral)

Indeterminate for COVID-19

Does not fit Classic or Non-COVID-19 descriptors

Non-COVID-19

Pneumothorax / Lobar pneumonia / Pleural effusion(s) / Pulmonary oedema

Other

Quantifying disease

Mild / Moderate / Severe

Other findings

Codes for subsequent Radiology Information System search:

CVCX0 = Normal CVCX1 = Classic CVCX2 = Indeterminate CVCX3 = Non-COVID-19

Please consider case upload to https://bit.ly/BSTICovid19_Database

CXR Examples

Patient 1 36MFever SOB worsening over 8 days ?COVID

Basal and peripheral involvement

Mild

PCR +ve

• Patient 2 75M

• Presents COPD, productive cough ?COVID

• Peripheral and basal consolidation which is bilateral.

• Classic pattern.

• Severe

• PCR subsequently positive

Patient 3. 38F

Classic pattern, severe

PCR +ve

Patient 436 male

Dad COVID +, unwell 11/7, dry cough, SOB, high RR.

Lymphopenia

First swab –ve, repeat swab +ve

Patient 5PCR positive at time of reporting.

This film would normally be reported as not compatible with COVID-19

Patient 840mFeverlow sats ?COVID ?LRTI

Vague opacity but non specific. Reported as normal.

Patient 8CT performed subsequently

RT-PCR subsequently confirmed positive

CT

Sensitivity 85% Specificity 60% -same study

Findings: Peripheral ground glass. Crazy paving. Consolidation. Bronchovascularthickening. Reverse Halos.

Thromboembolism in COVID

• Several centres report increased incidence in an ITU setting. Pooled analysis suggests a figure of about 17%.

• Difficult to study true prevalence. Nottingham approach and study. Local rate about 3% in triage population

• Immunothrombosis versus embolism

• Anticoagulating all patients does not improve survival

• Criteria for diagnosing PE clinically difficult (D-dimer expected to be raised, patients with pneumonitis have similar symptoms)

• Difficult to exclude clinically

Thromboembolism in COVID

• Remember about renal impairment in COVID 19

• The original BSTI/NHSE algorithm remains the main stay of imaging advice, with CTPA reasonable to perform in severely ill Covid-19 patients if the outcome would influence initiation of therapeutic anticoagulation.

• A less severely ill patient with classic Covid-19 on CXR should not trigger a CTPA routinely.

• CTPA in symptomatic patients with Classic Covid-19 on CXR should ideally be reserved for ‘disproportionate hypoxia’, ‘discordant clinical picture’ or a ‘sudden clinical deterioration’.

• This should be mentioned in all CTPA requests.

• A presenting high D-Dimer in a patient with Covid-19, or an elevation/upward trend should not solely be used to trigger a CTPA.

• At all times, patient stability and infection control considerations must be weighed against the benefit of undertaking the CTPA, especially given the higher infectivity of the new variant.

• When reporting CTPA the radiologist should not use the term “PE” for those with just segmental and/or subsegmental changes but describe the changes and then suggest they may represent PE or immunothrombosis (e.g. “a filling defect is noted; whether or not this represents embolus or immunothrombosis is uncertain”).

• https://www.bsti.org.uk/media/resources/files/Rationale_for_CTPA_in_Covid_considerations_F.pdf

Post COVID fibrosis

• Few data.

• The prevalence of post-COVID-19 fibrosis will become apparent in time, but early analysis from patients with COVID-19 on discharge from hospital suggests a high rate of fibrotic lung function abnormalities. Overall, 51 (47%) of 108 patients had impaired gas transfer and 27 (25%) had reduced total lung capacity. This was much worse in patients with severe disease

• Reference below suggests 1/3 with severe COVID-19 pneumonitis have abnormality at 6 months on imaging

• 1). Han X, Fan Y, Alwalid O, Li N, Jia X, Yuan M, Li Y, Cao Y, Gu J, Wu H, Shi H. Six‐month follow-up chest CT findings after severe COVID‐19 pneumonia. Radiology (In Press) Google Scholar

CT

• Examples on Horos

Some take home

messages

References

• BSTI:

• https://www.bsti.org.uk/standards-clinical-guidelines/clinical-guidelines/bsti-nhse-covid-19-radiology-decision-support-tool/

• Radiopedia article:

• https://radiopaedia.org/articles/covid-19-4?lang=gb

• Cochrane review:

• https://www.cochrane.org/CD013639/INFECTN_how-accurate-chest-imaging-diagnosing-covid-19

• Paper on imaging findings:

• https://pubs.rsna.org/doi/10.1148/rg.2020200159

• RSNA COVID resources

• https://www.rsna.org/covid-19