Pulmonary circulation

IMAGING IN PULMONARY CIRCULATION DISEASE

1. IMAGING IN PULMONARY CIRCULATION DISEASE DR. AMIT RAUNIYAR 1 ST YEAR RESIDENT DEPARTMENT OF RADIOLOGY NAMS

2. PULMOMARY CIRCULATION The pulmonary circulation is unique in many ways as its appearance reflects the patho -physiological unit of ventilation and perfusion, e.g. its response to hypoxia is arterial constriction as opposed to arterial dilatation in the systemic circulation. Secondly, the pulmonary vasculature is 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. In addition it follows a dual flow model (both pulmonary and bronchial circulations supply the lung).

3. PULMONARY CIRCULATION ANATOMY The pulmonary trunk originates from the right ventricle. In adults the main pulmonary artery measures approximately 5 cm in length and is entirely enveloped within the pericardium. At about the level of the fifth thoracic vertebra, it divides into the longer right and the shorter left pulmonary artery.

4. The left pulmonary artery runs superiorly over the left main bronchus to enter the left hilum and bifurcates into an ascending and descending branch. The ascending branch then divides almost immediately into the apicoposterior and anterior segmental branches which supply the left upper lobe. The 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.

5. The 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.

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

7. 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.

8. Bronchial Arteries The place of origin as well as the number of the bronchial arteries is subject to considerable variation. 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.

9. 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. The bronchial arteries run into the hilum , where they branch parallel and close to the bronchus to the peripheral airways. The diameter of these arteries is small, usually 1–1.5 mm at its origin within the mediastinum .

10. 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.

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

12. 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.

13. At rest, only one-third of the capillaries are perfused ; with increasing cardiac output under stress, the remaining capillaries will be recruited by increasing pressure in order to contribute to gas exchange.

14. The hydrostatic pressure within the pulmonary capillaries tends to force fluid into the interstitium of the lung. This is partly counteracted by the plasma oncotic (colloid osmotic) pressure, which attracts fluid back into the capillaries. Imbalance of these pressure ratios can lead to abnormal fluid shift and thus overflow of fluid into the lung parenchyma.

15. 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 . If this process continues, it leads to alveolar fluid accumulation when gas exchange may become compromised

16. An important difference between the pulmonary and systemic vasculature is the response to hypoxia. In the pulmonary system hypoxia results in local vasoconstriction, causing diversion of blood to regions of better ventilation.

17. This homeostatic mechanism (Euler– Liljestrand reflex) is 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.

18. The blood circulation is influenced by gravity and body position. In the upright position, most blood perfusion volume is in the basal part of the lung as illustrated by increased lung parenchyma density and larger vessel calibres . In the apical part of the lung (zone I) the intraalveolar pressure is larger than the intravenous and intraarterial pressure independent of ventilation and blood volume. In the basal part of the lung (zone III) intravenous and intra-arterial pressure exceed the intra-alveolar pressure. In the middle part (zone II) the intra-arterial pressure is higher than the intra-alveolar pressure followed by the intravenous pressure. In a lying position zone I is ventrally localised and zone III dorsally accompanied by an apico -basal gradient. In case of acute volume overload or left cardiac failure, especially the vessels in zone III are affected

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

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. Septal lines can be differentiated from blood vessels as the latter are not visible in the outer 1 cm of the lung. In addition, deep septal lines do not branch uniformly (as is the case for blood vessels) and are seen with a greater clarity (as they represent a sheet of tissue) than a blood vessel of similar calibre .

25. 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.

26. Stage 3 : Alveolar oedema (>25) Bat wing appearance

27. Cardiogenic pulmonary edema. Heart failure Coronary artery disease with left ventricular failure. Cardiac arrhythmias Fluid overload -- for example, kidney failure. Cardiomyopathy Obstructing valvular lesions -- for example,mitral stenosis Myocarditis and infectious endocarditis

28. 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)

29. The key findings of cardiogenic pulmonary edema Kerley B lines ( septal lines) Pleural effusions Usually bilateral, frequently the right side being larger than the left If unilateral, more often on the right Fluid in the fissures Thickening of the major or minor fissure Peribronchial cuffing Visualization of small doughnut-shaped rings representing fluid in thickened bronchial walls The heart may or may not be enlarged When the fluid  enters the alveoli themselves, the airspace disease is typically diffuse, and there are no air bronchograms

30. Non- cardiogenic pulmonary edema Bilateral, peripheral air space disease with air bronchograms or central bat-wing pattern Kerley B lines and pleural effusions are uncommon Typically occurs 48 hours or more after the initial insult Stabilizes at around five days and may take weeks to completely clear On CT Gravity-dependent consolidation or ground glass opacification Air bronchograms are common

31. Cardiogenic vs non cardiogenic edema

32. 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.

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

34. Vascular Signs A diameter of the main pulmonary artery at the level of its bifurcation > 29 mm was found to have a sensitivity of 87% at a specificity of 89% for diagnosis of PH.

35. main pulmonary artery (pulmonary trunk) to ascending aorta ratio higher ratio correlates with higher PA pressure the ratio obtained on the axial image at the bifurcation of the right pulmonary artery adult: normal ratio is less than 1.0 children: normal up to a ratio of around 1.09 A PA : AA ratio > 1 is highly specific

36. 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.

37. 16

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

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

40. 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

41. Reflux of contrast medium into the inferior cava and hepatic veins is seen in association with tricuspid regurgitation secondary to PH. Fluid collection in the anterior pericardiac recess (> 10–15 mm in depth) has been reported in association with increased ventricular strain in association with PH.

42. 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 ( socalled neovascularity ) arising from centrolobular arteries. Diffuse centrilobular acinar opacities Alternatively, thickened interlobular septa described as being suggestive for pulmonary veno -occlusive disease.

43. Pulmonary Arteriovenous Malformations Pulmonary arteriovenous malformations (PAVMs) may be 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.

44. 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.

45. Two types of PAVMs can be differentiated: 1. The simple type, consisting of a single feeding artery and one or several draining veins (80%). 2. A complex PAVM, consisting of more than one feeding arteries and one or more draining veins (20%).

46. 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. Pulmonary angiography has been considered the ‘gold standard’ for the diagnosis of PAVMs

47. 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

48. 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

49. 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

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

51. 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.

52. 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 pelvic, renal, or upper extremity veins and the right heart chambers.

53. 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.

54. 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.

55. Most patients with PE - no obvious symptoms at presentation. The most common symptoms of PE in the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study were: dyspnea (73%), pleuritic chest pain (66%), cough (37%), and hemoptysis (13%).

56. The classic clinical triad of sudden chest pain, dyspnoea and haemoptysis is present in only the minority of the cases. Other symptoms and signs may be: cough, syncope, tachycardia, fever, signs of DVT

57. 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

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

59. Pulmomary embolism clinical prediction Wells criteria Geneva score Pulmonary embolism rule out criteria(PERC)

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

61. 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. The value of D- dimer is that a negative result can help to exclude pulmonary embolism.

62. 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. The most important ones being:

63. CXR findings Fleischner sign: enlarged pulmonary artery (20%) Hampton hump: peripheral wedge of airspace opacity and implies lung infarction (20%) Westermark sign: regional oligaemia and highest positive predictive value (10%) pleural effusion (35%) knuckle 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 peripheral airspace opacities, diaphragmatic elevation and linear atelectasis .

64. Chest x-ray in pulmonary infarct Radiographic features that suggest infarction include the presence of a pleural effusion and the development of a pleurabased wedge-shaped opacity (Hampton hump). Hampton’s hump : peripheral wedge shaped pleural based opacity with apex pointing toward hilum , usually in lower lung zones.

65. 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.

66. Hampton’s hump

67. 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.

68. 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.

69. 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.

70. The lung is uniformly perfused and ventilated

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

72. CT Pulmonary angiography Helical CT is rapidly replacing scintigraphy as the imaging modality of choice in the assessment of patients with suspected PTE. 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. Multi– detector row helical CT will allow more reliable identification of subsegmental emboli than does single-detector helical CT. 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 ).

73. 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.

74. Polomint sign

75. 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. MR Magnetic resonance imaging (MRI) is an attractive alternative to CTA as no ionising radiation is used and modern MRI contrast media yield less risk for the development of contrast-related nephropathy and allergic reactions as compared to iodinated contrast media. According to the literature, the 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 demosrate filling defect in the branch of left descending pulmonary artery

80. R L

81. Echocardiography May directly visualize embolize 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.

82. 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%).

83. Compression Ultrasound 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 Textbook of radiology and imaging David Sutton 7 th edition Grainger and Allison’s Diagnostic Radiology 6 th edition Fundamentals of Diagnostic Radiology Bryant & Helms 4 th edition Radiopedia

85. THANK YOU