Imaging in pulmonary circulation disease

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. I n 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 C a ++ channels  smooth muscle contraction of PA. Additional channels and mechanism: TRPC6 (transient receptor potential canonical 6), TRPV4 (transient receptor potential vanilloid 4). Recently it i s proposed that hypoxia is sensed at the alveolar/capillary level  transducted to pulmonary artery smooth muscles via gap junctions .

16. responsible for ‘matched defects’ seen in cases of pneumonic consolidation on ventilation–perfusion imaging. This mechanism is also responsible for different vascular calibres in patients with lobular air trapping , as seen in ‘mosaic perfusion’ caused by pulmonary embolism .

17. 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.

18. 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

25. 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

26. 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)

27. Cardiogenic vs non cardiogenic edema

28. 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.

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

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

31. 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.

32. 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.

33. 16

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

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

36. 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

37. 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

38. 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.

39. 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

40. 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.

41. 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

42. Pulmonary plethora Pulmonary plethora is a term used to describe the appearances of increased pulmonary perfusion on chest radiographs. Pathology left-to-right cardiac shunts, e.g. ASD, VSD, PDA partial or total anomalous pulmonary venous return transposition of the great arteries truncus arteriosus Hyperdynamic circulation

43. Signs of plethora 1 Presence of shunt vessels ,end on vessels more than 2 times the diameter of accompanying bronchus 2. Prominent upper and lower zone vessels . En-face vessels below 10 th posterior rib Prominent vessels below the crest of diaphragm RDPA diameter more than that of trachea RDPA >16mm in diameter >6 vessels in peripheral one third of lung Prominent hilar vessels on lateral view In infants and children ,generalized mottling seen

44. Plain radiograph prominent pulmonary vasculature pulmonary vessels are dilated and tortuous extending farther into the peripheral one-thirds of the lungs diameter of a pulmonary artery is greater than the accompanying bronchus Equalisation in size of upper and lower zone vessels. increased size of number of hilar pulmonary arteries >3-5 end-on should be seen diameter of the right descending pulmonary artery is bigger than the diameter of the trachea cardiomegaly may be present

45. Pulmonary oligaemia Below normal flow through the pulmonary circuit. Congenital heart disease- right to left shunting. CXR- generalised decrease in size of the pulmonary vessels in all zones.

46. 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.

47. 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.

48. 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.

49. 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.

50. 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.

51. 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

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

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

54. Wells score

55. Geneva score

56. 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.

57. PIOPED criteria

58. PIOPED/PISAPED Criteria

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

60. 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%)

61. 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.

62. 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.

63. 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 2 o infection or sepsis.

64. Hampton’s hump

65. 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.

66. 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.

67. 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.

68. The probability that perfusion defects are due to pulmonary embolism increases with: increasing size and number, the presence of a wedged shape and the presence of a normal ventilation scan (“mismatched” defect). Mismatched perfusion defects that are segmental or larger are termed “high-probability” defects. A single mismatched defect is associated with a prevalence of pulmonary embolism of about 80%, whereas this prevalence is ≥ 90% with 3 or more defects. Limitations: Many studies are non-diagnostic Challenging to evaluate in pts with underlying airway disease ( eg COPD)

69. The lung is uniformly perfused and ventilated

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

71. 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).

72. CTPA findings in acute PE 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. 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. A peripheral intraluminal filling defect that forms acute angles with the arterial wall.

73. Polomint sign

74. 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 .

75. 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.

76. 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.

77. 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 .

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

79. 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.

80. 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%).

81. 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

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

83. THANK YOU!