Pulmonary Thromboembolic Disease

·     Age

o       Usually occurs after 60 years of age

· Cause

o       Most common cause is deep vein thrombosis (DVT) of lower extremity in >90%

· Predisposing factors

o       Immobilization (56%)

o       Surgery (54%)

· Pathophysiology

o       Clot from deep veins of leg breaks off

o       Travels via venous system to right side of heart

o       Fragments in right side of heart

o       Showers lung with emboli varying in size

§         On average > 6-8 vessels are embolized

· Clinical findings

o       Hemoptysis (25-34%)

o       Pleural friction rub

o       Thrombophlebitis

§         But only about 10-33% of patients with fatal pulmonary embolism (PE) are symptomatic for DVT

o       Acute dyspnea (81-86%)

o       Pleuritic chest pain (58-72%)

o       Apprehension (59%)

o       Cough (54-70%)

o       Tachycardia

o       Tachypnea

o       Accentuated 2nd heart sound

o       EKG changes (83%)

§         Mostly nonspecific

o       Elevated levels of fibrinopeptide-a (fpa) = small peptide split off of fibrinogen during fibrin generation

o       Positive d-dimer assay (generated during clot lysis)

· Location of pulmonary emboli

o       Bilateral emboli in 45%

o       Right lung only in 36%

o       Left lung only in 18%

o       Multiple emboli [3-6 on average] in 2/3

· Distribution by lobe

o       Lower lobes more often than upper lobes

o       RUL (16%)

o       RML (9%)

o       RLL (25%)

o       LUL (14%)

o       LLL (26%)

· Site ─ central versus peripheral

o       Central = segmental or larger veins in 58%

o       Peripheral = subsegmental or smaller veins in 42%

o       In subsegmental branches exclusively in 30%

o       Emboli are occlusive in 40%

·         Resolution of pulmonary embolism

o       Through fibrinolysis and fragmentation

o       By time interval

§         In 8% by 24 hours

§         56% by 14 days

§         77% by 7 months

o       By completeness

§         Complete in 65%

§         Partial in 23%

§         No resolution in 12%

§         Resolution less favorable with increasing age and cardiac disease

· Embolism without infarction (90%)

o       Dual blood supply of lungs ─ pulmonary and bronchial

· Imaging findings in embolic disease without infarction

o       Normal chest film common

o       Normal chest x-ray has a negative predictive value of only 74%

o       Plate-like (subsegmental, discoid) atelectasis

o       Lobar consolidation in lower lung zones and pleural effusion (most common findings with the lowest positive predictive value)

o       Westermark sign represents an area of oligemia (due to vasoconstriction distal to embolus)

§         Uncommonly seen

Axial CT image just below level of tracheal bifurcation demonstrates large intraluminal filling defects
in both right and left pulmonary arteries representing a "saddle embolus" straddling
the pulmonary arteries.

Pulmonary embolism. There is a large filling defect (white arrows) in the right pulmonary artery representing clot.

o Fleischner sign refers to local widening of artery by impaction of embolus (due to distension by clot / pulmonary hypertension developing secondary to peripheral embolization)

o      "Knuckle sign" is term used for abrupt tapering of an occluded vessel distally

· Imaging findings in embolism with infarction

o       Segmentally distributed wedge-shaped consolidation (54%)

§         With or without cavitation

o       Hampton hump is a pleural-based area of consolidation in the form of a truncated cone with base against pleural surface

o       Pleural effusion  in slightly over 50%

§         Thoracentesis

·         Bloody (65%)

·         Predominantly PMNs (61%)

·         Exudate (65%)

o       Usually no air-bronchogram because of hemorrhage into alveoli

o       "Melting sign" is the sign that refers to disappearance of the opacification within few days to weeks from periphery toward center

o       Fleischner lines = long-line shadows (fibrotic scar)

o       Plate-like (subsegmental, discoid) atelectasis (27%)

o       Cardiomegaly or CHF (17%)

o       Elevated hemidiaphragm (17%)

o       Subsequent nodular or linear scar more often than pneumonia leads to scarring

Hampton Hump. Axial CT scan of the chest shows bilateral filling defects in both pulmonary arteries (white arrows) representing thrombi. There is a large, wedge-shaped, pleural-based soft tissue density that represents the infarct and is called a Hampton Hump.

· CT findings (can be equal to angio in detection of emboli within proximal arteries):

o       Subsegmental intraluminal filling defects may not be detectable

o       Detection is poorer in middle lobe and lingular branches

o       Peripheral wedge-shaped lung densities with the triangle base adjacent to pleural surface

o       Peripheral rimlike contrast enhancement in a pulmonary artery

o       Intraluminal filling defect in pulmonary artery

· NUC (VQ scan = guide for angiographic evaluation)

·   Interpreted in reference to Biello or PIOPED criteria

o       Low- / intermediate-probability scans (73%)

§         Additional studies recommended

o       High-probability scan

§         In 12% normal angiogram

·         Angiographic findings

o       Intraluminal defect (94%)

o       Abrupt termination of pulmonary arterial branch

o       Pruning and attenuation of branches

o       Wedge-shaped parenchymal hypovascularity

o       Absence of draining vein in affected segment

o       Tortuous arterial collaterals

o       Complications of pulmonary angiography

§         Arrhythmia, endocardial injury, cardiac perforation, cardiac arrest, contrast reaction