·         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.

 

 

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

·         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