Imaging in pulmonary circulation disease by Dr. Milan silwal

1. IMAGING IN PULMONARY
CIRCULATION DISEASES
DR. Milan Silwal
Resident, MD Radiodiagnosis
NAMS

2. Presentation outline
• Pulmonary Circulation
• Pulmonary venous hypertension
• Pulmonary arterial hypertension
• Pulmonary AV malformations
• Pulmonary embolism

3. Pulmonary circulation: anatomy
• is unique in many ways:
– its response to hypoxia is arterial constriction
(as opposed to arterial dilatation in the systemic
circulation).
– directly influenced by cardiac function and vice
versa (as venous congestion is caused due to left heart
failure or pulmonary hypertension causing right ventricular
dysfunction or even failure).
– it follows a dual flow model (both pulmonary
and bronchial circulations supply the lung).

4. Pulmonary Arteries
• Pulmonary trunk originates from the right ventricle.
• approx. 5 cm in length and is entirely enveloped
within the pericardium.
• At about the level of T5, it divides into the longer
right and the shorter left pulmonary artery.
• In adults, the upper limit for the diameter of the
pulmonary trunk is 29–33 mm (for female: 27 mm),
and for the right and left pulmonary artery 23 and 22
mm, respectively.

5. • Left pulmonary artery: runs superiorly over the left main
bronchus to enter the left hilum and bifurcates into an
ascending and descending branch.
• Ascending branch then divides almost immediately into the
apicoposterior and anterior segmental branches which supply
the left upper lobe.
• Descending branch gives a branch to the lingula which itself
divides into two segmental arteries (superior and inferior
lingular segmental artery).
• The next branch from the descending branch is the superior
segmental artery, supplying the superior segment of the left
lower lobe .
• Subsequent branches supply the remaining segments of the
left lower lobe.

6. • Right pulmonary artery runs under the aortic arch, posterior
to the superior vena cava and anterior to the right main
bronchus, and just before entering the hilum it divides into
the ascending (truncus anterior) and the descending
(interlobar) branch.
• The ascending branch divides into apical, anterior and
posterior segmental branches.
• The interlobar artery gives rise to the middle lobe artery
(which further divides into the lateral and medial segmental
branches) and the right lower lobe artery, which immediately
gives off the artery to the superior segment of the right lower
lobe.
• As on the left side, subsequent branches supply the remaining
4 segments of the right lower lobe.

7. • The arterial branching follows and runs parallel to
the divisions of the bronchial tree (and having the
same name), supplying each bronchopulmonary
segment.

8. Pulmonary Veins
• The pulmonary veins, classically two on each side, transport
the oxygenated blood from the lung back to the left
atrium of the heart.
• The veins run independently from the pulmonary arteries
and bronchi towards the heart.
• The superior pulmonary veins drain the blood from the
upper lobes, including the middle lobe on the right side;
the inferior pulmonary veins drain the lower lobes.
• In addition, the veins from the visceral pleura drain into
the pulmonary veins, whereas the veins of the parietal
pleura drain into the systemic circulation via the veins of
the thoracic wall.

9. Bronchial Arteries
• bronchial arteries are responsible for 1% of the
lung blood flow but they are the major high-
pressure oxygenated blood supplier.
• In more than 70%, the bronchial arteries arise
from the descending thoracic aorta, most
commonly between the levels of T5 and T6.
• In most individuals there are 2 to 4 bronchial
arteries present, arising either independently or
from a common trunk; and a single right
bronchial artery.

10. • The right bronchial artery usually (78%) arises
within a common stem, with the first aortic
intercostal (intercostobronchial artery) from
the posteromedial aspect of the descending
aorta.
• On the left side, there is generally a superior
and an inferior branch, both arising from the
anterior aspect of the descending thoracic
aorta.

11. • Anomalous bronchial arteries, defined as
bronchial arteries that originate outside the
levels of T5 and T6, are found in up to 21% of
patients with haemoptysis.
• These anomalous arteries arise in the majority
of cases arise from the aortic arch.

12. Bronchial veins
• The bronchial veins drain into the pulmonary
veins and to a lesser extent into azygous vein.

13. Pulmonary circulation: physiology
• The pulmonary circulation is, unlike the
systemic circulation, a low-pressure system.
• There is only a relatively small pressure
difference between the pulmonary arteries
(mean pressure 12–20 mmHg) and the left
atrium(7–12 mmHg).
• The pressure in the capillaries and the veins
approximates the pressure in the left atrium.

14. • The pulmonary interstitial space is
usually kept dry by pulmonary
lymphatic channels.
• They drain any excess fluid which
enters the interstitium from the
alveoli.
• However, if the rate of accumulation
of fluid exceeds the capacity of
lymphatic clearance, fluid will begin
to accumulate within the
interstitium.

15. Euler–Liljestrand reflex (HPV)
• In the pulmonary system hypoxia results in local
vasoconstriction, causing diversion of blood to regions of
better ventilation.
• Hypoxia  hypoxia sensitive voltage gated K+ channels 
depolarization voltage gated Ca++ channels  smooth
muscle contraction of PA.
• Additional channels and mechanism: TRPC6 (transient
receptor potential canonical 6), TRPV4 (transient receptor
potential vanilloid 4).
• Recently it is proposed that hypoxia is sensed at the
alveolar/capillary level transducted to pulmonary artery
smooth muscles via gap junctions .

16. • blood circulation is
influenced by gravity and
body position.
• In case of acute volume
overload or left cardiac
failure, especially the
vessels in zone III are
affected.

17. Pulmonary Venous Hypertension
• PVH is caused by increased resistance in the
pulmonary veins and is elevation of the mean
pressure > 12 mmHg.
(Normal: 8-12 mm of Hg).

19. > 50

20. Pulmonary venous hypertension
• Stage 1: cephalisation
of the blood flow (12-19
mm of Hg)
• The upper zone vessels
are frequently as large
as or larger in diameter
than the lower zone
vessels.

21. RDPA >16

22. Stage 2: interstitial edema
,pleural effusion (20-
25mm Hg)
– Kerley lines
– peribronchial cuffing
and tram tracking
– perihilar haze
– Thickening of the
interlobar fissures
(subpleural edema)

23. • Typical radiological signs of an interstitial oedema are interstitial
(Kerley) lines
• Kerley lines- thickening of the interlobular septa as a result of fluid
accumulation within the lung.
• Kerley B lines are the most obvious ones and are short (1 cm or less)
interlobular septal lines, found predominantly in the lower zones
peripherally, and parallel to each other but at right angles to the
pleural surface.
• Kerley A lines are deep septal lines (lymphatic channels), radiating
from the periphery (not reaching the pleura) into the central
portions of the lung and approximately 4 cm long.
• Their presence normally indicates a more acute or severe degree of
oedema.

24. Stage 3
• This is termed alveolar
oedema.
• Kerley B lines
• airspace nodules,
• bilateral symmetric
consolidation in the mid
and lower lung zones
• and pleural effusions
may be seen. Stage 3 Alveolar oedema (>25)
‘Bat wing’ appearance

26. Cardiogenic pulmonary edema
– Heart failure
– Coronary artery disease with left ventricular failure.
– Cardiac arrhythmias
– Fluid overload : e.g.- renal failure.
– Cardiomyopathy
– Obstructing valvular lesions : e.g.- mitral stenosis
– Myocarditis and infectious endocarditis

27. Non-cardiogenic pulmonary edema
– Smoke inhalation.
– Head trauma
– Overwhelming sepsis.
– Hypovolemia shock
– Re-expansion
• By drainage of a large pleural effusion with thoracentesis
• Of the lung collapsed by a large pneumothorax
– High altitude pulmonary edema
– Disseminated intravascular coagulopathy (DIC)
– Near-drowning
– Overwhelming aspiration
– Heroin overdose
– acute respiratory distress (deficiency) syndrome (ARDS)

28. Cardiogenic vs non cardiogenic edema

29. Pulmonary Arterial Hypertension
• Haemodynamically it is defined as a systolic
pulmonary artery pressure of > 35 mmHg or a
mean pulmonary artery pressure of > 25
mmHg at rest or > 30 mmHg with exertion.

31. Plain radiograph
• elevated cardiac apex due to right ventricular
hypertrophy
• enlarged right atrium
• enlarged pulmonary arteries
• pruning of peripheral pulmonary vessels

32. • Vascular Signs
• A diameter of the main pulmonary artery at
the level of its bifurcation > 29 mm. ( Sn= 87%,
Sp= 89%)

33. Main pulmonary artery
(pulmonary trunk) to
ascending aorta ratio:
– higher ratio correlates
with higher PA pressure
– adult: normal ratio is less
than 1.0
– children: normal up to a
ratio of around 1.09
PA : AA ratio > 1 is highly
specific
A case of PAH with major increase in the calibre of the
pulmonary trunk with a pulmonary trunk/ascending
aorta ratio around 2.

34. • Enlarged pulmonary
arteries
• The maximum diameter
of the descending branch
of the pulmonary artery
measured 1 cm lateral
and 1 cm inferior to the
hilar point is 16mm for
males and 15 mm for
females.

35. 16

36. Pruning of peripheral pulmonary
vessels
• Rapid tapering of
peripheral vessels in
comparison to central
vessels

37. • Dilatation of bronchial arteries (> 1.5 mm) is
an indicator that they participate in blood
oxygenation due to (major) occlusion of
pulmonary arteries

38. • Cardiac Signs
Flattening and later bowing of the
cardiac septum and dilatation of
the short-axis diameter of RV as
compared to the LV (RV:LV >1)
are indicative of increased
pulmonary pressure,
though most of experience with
respect to the usefulness of this
sign refers to acute pulmonary
embolism

39. Parenchymal Signs:
• Mosaic perfusion is a hallmark of CTEPH, reflecting
peripheral vascular obstruction.
• In patients with Eisenmenger and IPAH, tiny
serpiginous intrapulmonary vessels may be seen (so
called neovascularity) arising from centrilobular
arteries.
• Diffuse centrilobular acinar opacities

40. Pulmonary Arteriovenous Malformations
• Rare vascular anomalies of lung, abnormally
dilated vessels provide a right-to-left shunt
between the pulmonary artery and vein.
• F: M = 1.5-1.8:1, p= 2-3/100,000
• diagnosed on clinical grounds and/or by familial
screening in patients with hereditary
haemorrhagic telangiectasia (HHT).
• When acquired, they may be seen in conjunction
with liver cirrhosis, schistosomiasis and
metastatic thyroid carcinoma.

41. • They can be classified as simple, complex or
diffuse.
• simple type: commonest; has a single segmental
artery feeding the malformation (~75%).
• complex type: have multiple segmental feeding
arteries (~20% )
• diffuse type: rare (~5% of lesions); the diffuse
form of the disease is characterised by hundreds
of malformations; some patients can have a
combination of simple and complex AVMs within
a diffuse lesion

42. • Usually asymptomatic,
• Clinically they may produce systemic arterial
desaturation and give rise to signs of dyspnoea,
hypoxia, cyanosis and heart failure.
• When they rupture, massive haemoptysis and
haemothorax occur.
• Direct communication between a pulmonary
artery and vein causes paradoxical embolism,
which is responsible for two-thirds of
neurological symptoms in patients with HHT.

43. • Radiographically they may
appear as round, oval, or
lobulated opacities with an
associated prominent vascular
shadow, but if small and discrete they
may not be detected on plain chest
radiography.
• They occur most frequently in
the lower lobes (50-70%)-
often unilateral.
• Pulmonary angiography has
been considered the ‘gold
standard’ for the diagnosis of
PAVMs

44. PULMONARY EMBOLISM
• Pulmonary embolism refers to obstruction of
the pulmonary artery (or one of its branches)
by material (thrombus, air, fat or tumor)
originating from elsewhere in the body.

45. In more than 90% of the cases the thrombus
originates from the deep veins of the legs or
pelvis (deep vein thrombosis; DVT)
– Rarely originate in the renal, or upper
extremity veins and the right heart chambers.

46. Pathophysiology
• Thrombus in Deep
veins in lower limb
• Breaks Emboli
formation moves to
right heart
• then to pulmonary
circulation to lodge
in pulmonary
vascular bed.

47. • Large thrombi - bifurcation of the main
pulmonary artery -saddle embolus -
hemodynamic compromise
• Smaller thrombi – occlude smaller vessels in
the lung periphery.
– more likely to produce pleuritic chest pain by
initiating an inflammatory response adjacent
to the parietal pleura.
Most pulmonary emboli are multiple, and the lower lobes
are involved more commonly than the upper lobes.

48. • Most patients with PE - no obvious symptoms at
presentation.
• The most common symptoms of PE:
– dyspnea (73%),
– pleuritic chest pain (66%),
– cough (37%), and
– hemoptysis (13%).
– Other: syncope, tachycardia, fever, signs of DVT
• The classic clinical triad of sudden chest pain,
dyspnoea and haemoptysis is present in only the
minority of the cases.

49. Causes of PE
• Venous stasis
• Hypercoagulable states
• Immobilization
• Surgery and trauma
• Pregnancy
• OCPs and estrogen
replacement
• Malignancy
• Others
– Stroke
– Indwelling venous
catheters
– Previous h/o venous
thromboembolism
– Congestive heart failure
– Fractures of long bone
– Obesity
– Varicose veins
– Inflammatory bowel
disease
Risk factors for the development of PE are related to Virchow’s
triad: 1) endothelial injury, 2) venous stasis, 3) blood
hypercoagulabilty

50. Consequences
– Increased alveolar dead space
– Hypoxemia
– Hyperventilation
– Pulmonary infarction
– Loss of surfactant- alveolar collapse
– Pulmonary hypertension

51. Pulmonary embolism prediction
• Wells criteria
• Geneva score
• Pulmonary embolism rule-out criteria(PERC)
• PIOPED/PISAPED criteria

52. Wells score

53. Geneva score

54. Pulmonary embolism rule-out criteria(PERC)
Criteria
– age <50
– pulse <100 bpm
– oxygen saturation >95% on room air
– absence of unilateral leg swelling
– absence of haemoptysis
– no recent trauma or surgery
– no prior history of venous thromboembolism
– no exogenous oestrogen use
Interpretation
– If the patient is deemed low risk and meet all of the criteria then there is no
need for further PE workup.
– If the patient is deemed low risk but is positive for any of the above criteria,
a d-dimer should be considered.
– If a d-dimer is positive, further investigation such as CTPA or V/Q scan may be
indicated.

55. PIOPED criteria

56. Investigations
• D- dimer assay
• Plain radiograph(CXR)
• Conventional pulmonary angiography
• CT pulmonary angiography
• ventilation/perfusion (V/Q) scan
• MRI
• Ultrasound

57. D-dimer assay
• D-dimer is formed when cross-linked fibrin is lysed by
plasmin, and elevated levels usually occur with
pulmonary embolism.
• However, because elevations of D-dimer are
nonspecific (e.g., increased by aging, inflammation,
cancer), an abnormal result has a low positive
predictive value. (Sn=99.5%, Sp=41%)

58. Plain Chest Radiography
• The chest X-ray may be normal (up to 40% of
patients with PE) or show non-specific findings,
even in extensive PE.
• The chest X-ray is performed not to diagnose PE
but to exclude other causes of the symptoms,
such as pneumonia, pleuritis, or pneumothorax.
• Although they are infrequently present, yet non-
specific, there are several signs related to PE and
therefore suggestive but still they do not confirm
the diagnosis of PE.

59. CXR findings…
• Hampton hump: peripheral wedge of airspace opacity and implies
lung infarction (20%)
• Westermark sign: regional oligaemia and highest positive predictive
value (10%)
• Fleischner sign: enlarged pulmonary artery (20%)
• knuckle sign or sausage sign- abrupt tapering or cutoff of a
pulmonary artery secondary to embolus.
• Palla sign : enlarged right descending pulmonary artery
• Chang sign : dilated right descending pulmonary artery with
sudden cut-off
• pleural effusion (35%)
• peripheral airspace opacities, diaphragmatic elevation and linear
atelectasis.

60. • Evolution: can take months to resolve and
leave linear scars (Fleischner lines) or pleural
thickening
• Infarcts “melts” (maintain shape, gradually
shrink); pneumonia and edema “fade” away
• Rarely cavitates unless 2o infection or sepsis.

61. Hampton’s hump

62. Ventilation–perfusion lung scanning
• Previously the imaging of choice, now largely
replaced by CT
• Nuclear medicine study, sensitive for PE
• Lower cost, lower radiation dose.
• A normal perfusion scan excludes pulmonary
embolism, but is found in a minority (about
25%) of patients.

63. • Ventilation (V) scan: Tc-99m labeled microaerosol
agents(krypton-81m, xenon-133, or aerosolized Tc-99m
diethylenetriamine pentaacetic acid (DTPA) are inhaled
via a nebulizer and deposit on bronchoalveolar lining,
demonstrating areas of ventilated lung.
• Perfusion (Q) scan: Tc-99m labeled albumin is
injected, which lodge in precapillary arterioles,
demonstrating areas of perfused lung.
• Images are then obtained in eight projections:
anteroposterior, posteroanterior, right and left lateral,
and right and left anterior and posterior oblique views.

64. • A normal perfusion study rules out PE with
almost 100% certainty and further
investigation is not indicated.
• If a perfusion defect is present, further
imaging is warranted.

65. The lung is uniformly perfused and ventilated

66. • High probability VQ scan – large perfusion defect in lateral
basal and posterobasal segments in Posterior and LPO
projections

67. CT Pulmonary angiography
• Helical CT is rapidly replacing scintigraphy as the imaging
modality of choice in the assessment of patients with
suspected PTE. (Sn= 83% and Sp= 96%, )
• It is more accurate than scintigraphy and is rapid, noninvasive,
and readily available.
• Helical CT directly demonstrates intraluminal clot as a filling
defect.
• In addition, in patients without PTE, helical CT often provides
alternative diagnoses.
• Allows evaluation of DVT in the abdomen, pelvis, thighs, and
calves- scanning the lower limb 3-4 minutes after scanning the
pulmonary vessels( indirect venography).

68. CTPA findings in acute PE
1. Arterial occlusion with failure to enhance the entire
lumen due to a large filling defect; the artery may be
enlarged compared with adjacent patent vessels.
2. A partial filling defect surrounded by contrast material,
producing the “polo mint” sign on images acquired
perpendicular to the long axis of a vessel and the
“railway track” sign on longitudinal images of the
vessel.
3. A peripheral intraluminal filling defect that forms acute
angles with the arterial wall.

69. Polomint sign

72. Chronic pulmonary embolism
Diagnostic criteria:
• 1. A complete obstruction by a thrombus of a pulmonary artery that
shows a decrease in diameter as compared to surrounding non-obstructed
pulmonary arteries.
• 2. An eccentric partial intraluminal filling defect with an obtuse angle to
the vessel wall
• 3. An abrupt tapering of a vessel which is usually the consequence of
recanalisation of a previously completely obstructed pulmonary artery by
thrombus.
• 4. A thickening, sometimes irregularly, of the pulmonary arterial wall,
with narrowed lumen if recanalisation had occurred.
• 5. The presence of intraluminal webs or bands
• 6. An intraluminal filling defect with the morphology of an acute PE
present for > 3 months.

76. MRI
• Magnetic resonance
imaging (MRI) is an
attractive alternative to CTA
as no ionising radiation is
used.
• Accuracy of MRA is
comparable to CTPA for
central pulmonary arteries,
but still limited for PE in the
peripheral pulmonary
vessels.

77. • MRA also provide physiological information
including the regional distribution of
ventilation and perfusion.
• Less spatial resolution than CTA.
• MR angiography is as accurate as CT
angiography in demonstrating lobar and
segmental emboli.
• Currently plays a limited role in the imaging of
PE.

78. Conventional Angiogram
• Until recently, pulmonary angiography was
considered the gold standard for the diagnosis of
PE.
• For several reasons, e.g. costs, limited availability
and invasiveness of the procedure, it has not
gained general acceptance.
• Today the only indication for conventional
angiogram is patients in whom catheter directed
thrombectomy /thrombolysis is to be done.

79. • Conventional angiogram
coned down to demostrate
filling defect in the branch of
left descending pulmonary
artery

80. Echocardiography
• May directly visualize emboli or show right heart
hemodynamic changes that indirectly suggest pulmonary
embolism.
• The advantage of this technique is the assessment of other
cardiovascular diseases that may explain the patient’s
symptoms, such as cardiac tamponade or acute myocardial
Infarction.
• Indirect parameters such as unexplained right ventricular
dilatation/dysfunction and marked tricuspid regurgitation -
sensitivity of about 50% and a specificity of about 90% for
pulmonary embolism.

81. • Transthoracic echocardiography visualizes
intracardiac thrombi (usually right atrium) in
about 5% of patients with acute pulmonary
embolism and generally does not detect emboli
in the pulmonary arteries.
• Transesophageal echocardiography can visualize
thrombi in the central pulmonary arteries with
high specificity (> 90%), but its sensitivity has not
been evaluated in unselected patients with
pulmonary embolism (perhaps about 30%).

82. Compression US/Doppler US of the
Legs
• The majority of the PE originates from the deep venous
system of the lower extremities and pelvis.
• If DVT is diagnosed in a patient with clinically suspected PE,
no further evaluation is needed and the patient can be
treated for PE.
• In skilled hands compression ultrasound (CUS) achieves a
92–95% sensitivity and 98% specificity for the diagnosis of
acute DVT.
• However, the presence of DVT can be confirmed in only a
minority of patients with proven PE.
• A negative CUS of the legs, the best investigation to
evaluate DVT, does not exclude the presence of PE and
further imaging is warranted

84. References
• Grainger and Allison’s Diagnostic Radiology 6th
edition
• Textbook of radiology and imaging David
Sutton 7th edition
• http//www.radiopedia.org

85. THANK YOU!