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Pulmonary Embolism

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Historia

70 year old male with IPF (secondary to UIP, diagnosed by biopsy 2 months prior) was found to have deterioration of pulmonary function despite being on a 2-week trial of 20mg prednisone and home oxygen therapy.

Follow up Echocardiography  demonstrated normal left ventricular size and motion with estimated EF of 60-65%. RVSP of 40mmHg.


Wyniki

1. Multiple subsegmental mismatched perfusion defects in bilateral lungs more prominent in the basal segments

2. Mismatched segmental perfusion defect in the right posterior basal segment.

3. Decreased perfusion  of the entire right upper lobe seen as heterogenous perfusion in the RPO projection but appears more clearly hypoperfusion in the posterior projection.

4. The photopenic focus in the right upper lobe with peripheral perfusion ("stripe sign") is secondary to en-face hypoperfusion extending to the lateral periphery of the lung.


Diagnoza

Pulmonary Embolism


Dyskusja

This is a high probability V/Q scan based on Modified PIOPED II criteria. A follow up lower extremity duplex ultrasound demonstrated noncompressible/occluded posterior tibial and peroneal veins.

Follow up CTA demonstrated multiple filling defects in the branches of the right pulmonary artery with occlusive thrombosis of the right upper lobe anterior segmental artery and additional filling defects in the right lower lobe segmental and subsegmental arteries.

The interesting aspect of this case is that the right upper lobe perfusion defect is not indentified as segmental until the lateral projection is viewed.


Kluczowe punkty

1. Modified PIOPED II criteria for High probablity: 2 or more mismatched segmental defects; note that experienced readers should use a gestalt interpretation in conjunction with the known criteria (1)

2.  Often we come across ancillary findings not attributed to a thrombotic event (noted seperately in technical parameters), and readers should have a working knowledge of them.

3. RVSP can be estimated from echo using the doppler-derived velocity of the tricuspid regurgitation jet. Generally, an RVSP>34 mmHg (for screening only) should raise concern for pulmonary artery hypertension which is then diagnosed with a PA mean pressure >25 mmHg (occlusion pressure<15 mmHg)on cardiac catheterization (2).

4. Ancillary scintigraphic findings commonly used include(3):  artifacts (pacemakers), cephalization of blood floow secondary to pulmonary venous hypertension, stripe sign secondary to pleurally based bronchopulmonary segments (NPV 93%), Fissure sign secondary to pleural effusion or chronic parenchymal lung disease, or segmental countour pattern secondary to lymphangitic spread of carcinoma.

5. In clinical practice, ideally one should ask for an additional single breath ventilation; in this case in the posterior projection to compare with the perfusion defect of the right upper lobe.


Odnośniki

1)Parker, J. Anthony, et al. "SNM practice guideline for lung scintigraphy 4.0." Journal of nuclear medicine technology 40.1 (2012): 57-65.

(2)Minai, Omar A., and Marie M. Budev. "Diagnostic strategies for suspected pulmonary arterial hypertension: a primer for the internist." Cleveland Clinic journal of medicine 74.10 (2007): 737-747.



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