Lung ultrasound for pulmonary embolism

Images Edward Christian Text Genevieve Carbonatto

A 65 year old man presents to the Emergency Department with a 1 week of cough and left sided chest pain. The pain is intermittent but worse at night when lying down. It is not exacerbated by activity. The patient  is experiencing shortness of breath when the chest pain comes on. He has had subjective fevers and a dry non productive cough. He has chronic right lower leg swelling but no pain. There is no history of DVT or family history of thrombophilia. His past history includes paroxysmal AF and hypertension.

On examination his RR is 30, saturations 93% on 4l using nasal prongs. His HR is 94/min and his BP 115/56, temperature 36.5. There are a few crackles at his right base and some reduced air entry at his left base on auscultation.

His Chest Xray is unremarkable. No area of consolidation seen. He is in sinus rhythm and there are no acute ischaemic changes

Blood gas : pH 7.38, pCO2 40mmHg, HCO3  23 mmol/l, lactate 2.8

His WCC is 16 CRP 95

In view of his unremarkable chest Xray and the abscence of fever, an ECHO is performed to look for right heart strain in the context of a possible PE or evidence of a pericardial effusion in the context of a pericarditis.

This is his PLAX. His LV is small. His RV large in comparaison.

This is his PSAX: There is flattening of the interventricular septum indicating high RV pressure

This is his 4C view. The RV is dilated and  McConnell’s sign is present.

There is evidence of right heart strain on this basic ECHO. A PE is to be excluded.

A lung ultrasound is performed which shows a hypoechoic lesion at  the left base. It has a hyperechoic centre.

He has a vascular scan performed by the vascular lab in the emergency department which shows a thrombus in the popliteal vein. The vein also appears aneurysmal. He has a double popliteal vein (duplication of the femoral and popliteal veins is common, with a prevalence of 20% in the femoral vein segments and 35% in the popliteal vein) (5)

A CTPA confirms extensive bilateral pulmonary emboli and right heart strain. He is anticoagulated and transferred to ICU

Discussion:

The diagnosis of PE was made on ECHO in conjunction with the history and confirmed with a CT angiogram. The lung ultrasound was nevertheless interesting.

The use of ultrasound for detection of PE was  first described 40 years ago, largely ignored and then “rediscovered” 20 years ago (4). Lung ultrasound is not the best imaging modality for the diagnosis of PE but, in the acute situation, may be helpful.

There are some criteria which may help in the diagnosis of PE using ultrasound. These include:

  1. One lesion may be present but often multiple lesions are present ( 2 or 3)
  2. Hypoechoic , pleural – based parenchymal lesion –
  3. Usually wedge shaped (>85%)
  4. May be rounded or polygonal
  5. In 20% may  be associated with a central hyperechoic lesion indicating the presence of an air – filled bronchiole
  6. Lesions may be associated with a pleural effusion
  7. Using Colour Doppler, in pulmonary infarction, pulmonary arterial flow is not detected . This is termed “consolidation with little perfusion”
  8. A congested thromboembolic vessel may be visible called “vascular sign”
  9. The  posterior lower parts of the lung are affected most  ( > 70% ) of patients. The explanation for this is not clear but may be due the anatomic structure of the pulmonary tree
  10. The right lung was affected more frequently than the left (66.7%)

The  presence of these findings supports the diagnosis of PE. The absence of these findings does not exclude a PE

The differential diagnosis includes

  1. Pneumonia
  2. ARDS
  3. Malignancy

In the literature, the sensitivity, specificity, and accuracy of ultrasound  for diagnosing PE is 74%-80%, 92%-95%, and 84%, respectively

Teaching point: Lung ultrasound is not the best modality to diagnose pulmonary embolism. CTPA is be the diagnostic modality of choice. In situations where clinical suspicion is high and CTPA is not available then ultrasound may be a valuable adjunct to confirm the diagnosis along with venous Doppler studies and ECHO.

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References

  1. Chest. 2005 Sep;128(3):1531-8.
    Thoracic ultrasound for diagnosing pulmonary embolism: a prospective multicenter study of 352 patients.
    Mathis G1, Blank W, Reissig A, Lechleitner P, Reuss J, Schuler A, Beckh S.
  2. Ann Thorac Med. 2013 Apr-Jun; 8(2): 99–104.
    The role of thoracic ultrasonography in the diagnosis of pulmonary embolism
    Sevda Sener Comert, Benan Caglayan, Ulku Akturk,1 Ali Fidan, Nesrin Kıral, Elif Parmaksız, Banu Salepci, and Betul Ayca Ozdere Kurtulus
  3. Chest June 2003Volume 123, Issue 6, Pages 2154–2155
    Lung Sonography in Pulmonary Embolism
    Angelika Reissig, MD, Claus Kroegel, MD, PhD, FCCP
  4. Chest. 2001 Dec;120(6):1977-83.
    Sonography of lung and pleura in pulmonary embolism: sonomorphologic characterization and comparison with spiral CT scanning.
    Reissig A1, Heyne JP, Kroegel C.
  5. https://www.sciencedirect.com/topics/neuroscience/popliteal-vein

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