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Thin section produces better contrast between lung parenchyma and bronchus and pulmonary vessel. A scan obtained with increased slice thickness, produces volume averaging with blurring of pathological details.
Effect of reconstruction algorithm on spatial resolution : As compared to Standard smooth algorithm, the sharp algorithm shows better resolution and edge delineation. Also, in contrast to the scan reconstructed using standard algorithm, 7.5 line pairs are easily resolved.
Image resolution improves on retrospective targeting.
The division of trachea gives rise to the left and right mainstream bronchi, which further divides into lobar and segmental bronchi. Segmental bronchi divides after 6 to 20 division they no longer contain cartilage in their walls and are referred to as bronchioles.
The lung parenchyma is supported by a network of connective tissue , called lung interstitum.
The abnormalities of subpleural interstitium is recognized over the costal surface and along fissuresNormal fissure is less than 1 mm thick, smooth and very thin opacities
Anatomy of the parietal pleura and chest wall in a section of a cadaver. The parietal pleura and endothoracic fascia are visible as a thin white layer, lining the thoracic cavity. Little extra thoracic fat is present in this example. The innermost intercostal muscle is visible external to the parietal pleura, measuring 1 to 2 mm in thickness. External to this is a layer of fat containing the intercostal vessels and nerve. The intercostal muscles are absent in the paravertebral regions; only parietal pleura, endothoracic fascia, and paravertebral fat are visible.Normal intercostal stripe and paravertebral line. On HRCT in a normal subject, the intercostal stripe is visible as a thin white line. Although it represents the combined thickness of visceral and parietal pleurae, the fluid-filled pleural space, endothoracic fascia, and innermost intercostal muscle, it primarily represents the innermost intercostal muscle. The intercostal stripe is seen as separate from the more external layers of the intercostal muscles because of a layer of intercostal fat. Posteriorly, the intercostal stripe is visible anterior to the lower edge of a rib. Only a very thin line (i.e., the paravertebral line) is visible in the paravertebral region.The paravertebral line. In the paravertebral regions (arrows), the innermost intercostal muscle is absent, and, at most, a very thin line (the paravertebral line) is present at the lung:chest wall interface. As in this case, a distinct line may not be seen.
Manifested by the interface sign, peribronchovascular interstitial thickening, interlobular septal thickening, Parenchymal band, subpleural interstitial thickening, intralobular interstitial thickening , honeycombing, irregular opacities and subpleural lines.
Described by Zerhouni et al. present in patients with interstitial abnormality regardless of cause. Associated with increased lung reticulation.
It is strong connective tissue sheath that envelops central bronchi and pulmonary arteries. This abnormality is perceived in HRCT as an increase in bronchial wall thickening (similar to peribronchial cuffing on chest X ray) and an increase in the diameter of pulmonary artery branches.The smooth PBIT are appreciated as kerley B lines in x ray.
1.Nodular peribronchovascular interstitial thickening in a patient with sarcoidosis. Numerous small nodules surround central bronchi and vessels.2.
Beaded or noularseptal thickening
Intralobular interstitial thickening reflects thickening of distal peribronchovascular interstitial tissue and the intralobular interstitium.Most commonly associated with lung fibrosis, like UIP or asbestosis.
Parenchymal bands represents areas of peribronchovascular fibrosis, coarse scars or atelectasis associated with lung infiltration or pleural fibrosis.
High-resolution CT scans of the right lung show peripheral, poorlydeﬁned, small centrilobular nodules and branching linear opacities of similar caliberoriginating from a single stalk (the tree-in-bud pattern)in the lower lobe. These ﬁndings represent endobronchial spread of tuberculosis. Postprimary active tuberculosis in a 34-year-old man with weight lossand a chronic cough. (a) High-resolution CT scan ofthe left lung shows a thick-walled cavity and multipleperipheral small nodules and branching linear structures
THE PATIENTS SYMPTOM IS IMPORTANT WHILE CONSIDERING THE DIFFERNETIAL OF GGO.
In general terms, the D/D of crazy paving is similar to GGO.
Results from imbalance between proteolytic and antiproteolytic enzymes ,the balance is shifted toward proteolysis by smoking or enzymatic deficiencies, such as a1-antiprotease deficiency .
The yellow arrows indicates the pulmonary vessels
Pulmonary tissue density is in part determined by the blood volume present within lung tissue. Any pathologic process that disturbs the distribution of pulmonary blood volume may alter pulmonary parenchymal attenuation. Alterations in pulmonary parenchymal attenuation that are seen on HRCT imaging that either result from infiltration of the lung parenchyma or from disturbances in pulmonary blood volume may be collectively referred to as ‘‘inhomogeneous lung opacity.’’
Technical aspect of hrct; normal lung anatomy & hrct findings of lung disease
TECHNICAL ASPECT OF HRCT; NORMALLUNG ANATOMY & HRCT FINDINGS OFLUNG DISEASE Presenter : Dr. Sarbesh Tiwari PGT Radiodiagnosis Assam Medical College Dibrugarh 1
HRCT ------ MEANINGo It is often used for anything and everything to do with “high resolution”.o Resolution : Means ability to resolve small object that are close together ,as separate form.Actual meaningo A scan performed using high- spatial frequency algorithm to accentuate the contrast between tissue of widely differing densities, eg., - air & vessels (lung) - air & bone (temporal & paranasal sinus) 2
INTRODUCTION• HRCT -- Use of thin section CT images (0.625 to 2 mm slice thickness) often with a high-spatial-frequency reconstruction algorithm to detect and characterize disease affecting the pulmonary parenchyma and airways.• Superior to chest radiography for detection of lung disease, points a specific diagnosis and helps in identification of reversible disease. 3
HISTORY• 1982– The term HRCT was first used by TODO et. Al• 1985 – Nakata et.al and Naidich et.al published first report on HRCT Since then has been an important tool in pulmonary medicine• Recent development of MDCT scanner capable of volumetric high resolution scanning has improved the investigation 4
TECHNICAL ASPECTParameterso Slice thicknesso Kvpo mAso Scan timeo FoVo Interslice gap (collimation)o Filming. 5
SLICE THICKNESS• Thin sections 0.5 – 1.5 mm is essential for optimal spatial resolution• Thicker slices are prone for volume averaging and reduces ability to resolve smaller structure• Better for delineation of bronchi, wall thickness and diameter 6
Reconstruction Algorithm• Denotes the frequency at which the acquired scan data are recorded when creating the image.• Using a high-resolution algorithm is critical element in performing HRCT.• High spatial frequency or sharp algorithm -- bone algorithm is used which reduces image smoothing and better depicts normal and abnormal parenchymal interface. 8
Kilovolts (Peak), Milliamperes, and Scan Time• In HRCT image, noise is more apparent than standard CT.• Noise – 1/√ mAs X Kvp X scan time• As increasing scan time is not feasible, mAs and Kvp are altered to reduce noise• Noise decreases with increase in Kvp and mAs. 10
• For routine technique – Kvp -- 120-140 mAs -- 200- 300• Increased patient and chest wall thickness are associated with increase image noise, may be reduced by increasing mAs and Kvp• Scan Time : As low as possible (1-2 sec) to minimize motion artifact. 11
WINDOW SETTINGSLung window• Window level setting ranging from – 600 to – 700 HU and window widths of 1000 to 1500 HU are appropriate for a routine lung window.Soft tissue window• Window level/width setting of 40-50/ 350-450 HU are best for evaluation of the mediastinum, hila, and pleura. 12
LOW DOSE HRCT• Low dose HRCT uses Kvp of 120- 140 and mA of 30-20 at 2 sec scan time.• Equivalent to conventional HRCT in 97 % of cases• Disadvantage : Fails to identify GGO in few cases and have more prominent streak artifact.• Not recommended for initial evaluation of patients with lung disease.• Indicated in following up patients with a known lung abnormality or in screening large populations at risk for lung ds. 13
Matrix size, Field of View, and Target reconstruction• Matrix size : Largest available matrix s/b used – 512 x 512• Field of view : smallest FOV that will encompass the patient is used as it will reduce the pixel size. (commonly 35 to 40)• Retrospectively targeting image reconstruction to a single lung instead of the entire thorax significantly reduces the FOV and image pixel size, and thus increases spatial resolution. 14
• INTERSLICE GAP – varies from examination to examination, but is usually 10- 20 mm• INSPIRATORY LEVEL : Routine HRCT is obtained in suspended full inspiration, which optimizes contrast between normal structures, various abnormalities and normal aerated lung parenchyma; and reduces transient atelectasis, a finding that may mimic or obscure significant abnormalities.• EXPIRATORY SCAN : valuable in obstructive lung disease or airway abnormality 16
Patient Position and the Use ofProne Scanning• Supine adequate in most instances.• Prone for diagnosing subtle lung abnormalities. e.g., asbestosis, suspected early lung fibrosis• Prone scan is useful in differentiating dependent lung atelectasis from early lung fibrosis 17
Axial CT image shows opacity in the posterior part of the lung which could representdependent opacity or pulmonary inflammation. The prone images shows completeresolution of the opacity suggesting dependent atelectasis. 18
Persistent opacity in the posterior lung in apatient with pulmonary fibrosis. 19
TECHNIQUE OF SCAN ACQUISITION:1. Spaced axial scans :• Obtained at 1cm intervals from lung apices to bases. In this manner, HRCT is intended to ―sample‖ lung anatomy• It is assumed that the findings seen at the levels scanned will be representative of what is present throughout the lungs• Results in low radiation dose as the individual scans are widely placed 20
2. Volumetric HRCT -• MDCT scanner are capable of rapid scanning and thin slice acquisition.Advantages : 1. Viewing of contagious slice for better delineation of lung abnormality 2. Complete imaging of lung and thorax 3. Reconstruction of scan data in any plane using MIPs or MinIPs. 4. diagnosis of other lung abnormalitiesDisadvantage : greater radiation dose. It delivers 3-5 times greater radiation. 21
Multidetector Helical HRCT• Multidetector CT is equipped with a multiple row detector array• Multiple images are acquired due to presence of multiple detectors• Advantages : - shorter acquisition times and retrospective creation of both thinner and thicker sections from the same raw data• Acquisition time is so short that whole-lung HRCT can be performed in one breath-hold. 22
Which is better HRCT or MD- HRCT• Various study shows the image quality of axial HRCT with multi-detector CT is equal to that with conventional single- detector CT.• HRCT performed with spaced axial images results in low radiation dose as compared with MD-HRCT.• Increased table speed may increase the volume- averaging artifact and may result in indistinctness of subtle pulmonary abnormalities.• MDCT provides for better reconstruction in Z axis 23
Radiation dose• Annual background radiation ----- --- 2.5 mSv• PA CHEST Radiograph ----- ----- ----- 0.05 mSv• Spaced axial HRCT (10mm space) ----- 0.7 mSv ( 14 X ray)• Spaced axial HRCT (20 mm space) ------ 0.35 mSv ( 7 X ray)• Low Dose Spaced axial HRCT -------- 0.02 mSV• MD-HRCT ---- ------- 4 - 7 msv ( 60-80 x ray)Combining HRCT scan at 20 mm interval with low mAs scan (40 mAs) would result in radiation comparable to conventional X ray. 24
HRCT ARTIFACT• Streak Artefacts : Fine, linear, or netlike opacities Radiate from the edges of sharply marginated , high-contrast structures such as bronchial walls, ribs, or vertebral bodies. More evident on low mA Mechanisms: beam hardening, photon starvation, and aliasing. 25
Motion-related artifacts• Pulsation / Star artefacts• Doubling artefacts.• Stair-step artefacts in sag/coro reconstruction. 26
MODIFICATION OF SCAN PROTOCOL Scan protocol can be modified in relation to disease or patients comfort. If a disease has basal predominance, it may be wise to begin scanning near the diaphragm and proceed cephalic . Caudad for disease with an upper-lobe predominance (e.g., sarcoidosis) An alternative approach - cephalad in all patients. 27
LUNG ANATOMY• Right lung is divided by major and minor fissure into 3 lobes and 10 broncho- pulmonary segments• Left lung is divided by major fissure into 2 lobes with a lingular lobe and 8 bronchopulmonary 1.1 kg segments 30
There are approximately 23generation of dichotomous branchingFrom trachea to the alveolar sacHRCT can identify upto 8th ordercentral bronchioles 32
TRACHEAL ANATOMY• 10-12 cm in length, from C6 level to upper border of D5.• Extrathoracic (2-4cm) and Intrathoracic(6-9 cm beyond manubrium)• In men, tracheal diameter – 25-27 mm women – 21- 23 mm• The posterior portion of the tracheal wall is a thin fibromuscular membrane----- allows for oesophageal expansion. 33
BRONCHIAL ANATOMY• Approximately 23 generations of branches from the trachea to the alveoli.• Bronchi with a wall thickness of less than 300 um is not visible on CT or HRCT.• As a consequence, normal bronchi less than 2 mm in diameter or closer than 2 cm from pleural surfaces equivalent to seventh to ninth order airways are generally below the resolution even of high-resolution CT 34
BRONCHUSBLOOD SUPPLY Bronchial Arteries— 2 on left side i.e. superior and inferior 1 on right side Left arises from thoracic aorta Right from either thoracic aorta, sup. left bronchial or right 3rd intercostal arteryVENOUS DRAINAGE on right- azygous vein on left- left superior intercostal or accessory hemiazygous vein• NERVE SUPPLY Pulmonary plexus at hilum (vagus and sympathetic) 35
BRONCHOARTERIAL RATIO (B/A)• Internal diameter of both bronchus and accompanying arterial diameter calculated and ratio measured.• Normal ratio is 0.65-0.70• B/A ratio >1 indicates bronchiectasis. NB:: B/A ratio increases with age and may exceed 1 in normal patients > 40 years. 36
SECONDARY PULMONARYLOBULE • Smallest lung unit that is surrounded by connective tissue septa (Miller) • The basic anatomic unit • Irregular polyhedral in shape. • Measures 1 to 2.5 cm 37
Anatomy of the Secondary Lobule and ItsComponents1. Interlobular septa and contiguous subpleural interstitium,2. Centrilobular structures, and3. Lobular parenchyma and acini. 38
Interlobular septa and contiguous subpleural interstitiumThe secondary pulmonary lobule is marginated by septa which extends from the pleural surface.They measure 0.1 mm in thickness.They are less well defined in central lungLobular core :The secondary lobule is supplied by arteries and bronchioles that measures approximately 1 mm in diameter.It consists of functioning lung parenchyma namely the alveoli, alveolar duct and vessels. The parenchyma is supported by network of central and peripheral fibers of interstitium. 39
PULMONARY ACINUS Portion of lung parenchyma supplied by a single respiratory Bronchiole. Size is 7 to 8 mm in adults 3 to 24 acini = Sec Pul. LobulePrimary Lobule: Lungparenchyma associated with asingle Alveolar duct.4-5 Primary Lobules Acinus 40
• The peribronchovascular interstitum invests the bronchi and pulmonary artery in the perihilar region.• The centrilobular interstitium are associated with small centrilobular bronchioles and arteries• The subpleural interstitium is located beneath the visceral pleura; envelops the lung into fibrous sac and sends connective tissue septa into lung parenchyma.• Interlobular septa constitute the septas arising from the subpleural interstitium. 49
The normal pulmonary veinbranches are seen marginatingpulmonary lobules. The centrilobularartery branches are visible as arounded dot 50
Anatomy of pleural surfaces and chest wall. 51
NORMAL LUNGATTENUATION• Normal lung attenuation : –700 to – 900 HU• Attenuation gradient : densest at dependent region of lung as a result of regional difference in blood and gas density due to gravity Difference in attenuation of anterior and posterior lung ranges from 50 – 100 HU• In children, lung attenuation is greater than adults. 52
NORMAL EXPIRATORY HRCT• Performed to detect air trapping in small airway obstruction• Attenuation increases with expiration (ranges from 100 to 130 HU)• 60 % of normal individual shows air trapping in the superior segment of lower lobe and involving single lobule, normal variant. 53
STRUCTURED APPROACHQ.1. What is the dominant HR-pattern ?Q.2. Where is it located within the secondary lobule (centrilobular, Perilymphatic or random) ?Q.3. Is there an upper versus lower zone or a central versus peripheral predominance ?Q.4. Are there additional findings (pleural fluid, lymphadenopathy, traction bronchiectasis) ? 55
LINEAR AND RETICULAR OPACITIES INCREASED NODULES AND LUNG NODULAR OPACITIES ATTENUATION PARENCHYMAL consolidation OPACIFICATION Ground glass HRCTPATTERN CYSTIC LESIONS, EMPHYSEMA, AND BRONCHIEACTASIS MOSAIC ATTENUATION AND PERFUSION DECREASED LUNG ATTENUATION AIR TRAPPING ON EXPIRATORY SCANS 56
LINEAR AND RETICULAR OPACITIES• Represents thickening of interstitial fibers of lung by - fluid or - fibrous tissue or - infiltration by cells 57
Interface signIrregular interfaces between theaerated lung parenchyma andbronchi, vessels, or visceralpleural surfaces.Represent thickened interlobularsepta, intralobular lines, orirregular scars.Nonspecific.Common in patients with an interstitial abnormality, fibroticlung disease. 58
Peribronchovascular Interstitial Thickening PBIT Irregular Smooth Nodular Venous, lymphatic or infiltrative lymphatic or disease infiltrative diseases Pulmonary edema/ Due tohemorrhage adjacent lung fibrosis SarcoidosisLymphoma / leukemia Lymphangitic Sarcoidosis,Lymphangitic spread of silicosis, TB spread of carcinoma and talcosis 59 carcinoma
INTERLOBULAR SEPTAL THICKENING• Normally, only a few septa seen• On HRCT, if numerous interlobular septas are seen, it almost always indicate abnormality.• Septal thickening d/t -interstitial fluid, cellular infiltration or fibrosis.• The thickened interstitium outline the secondary pulmonary lobules and are perpendicular to the pleura.• D/D are similar to that of PBIT. 61
Smooth Septal thickening Septal thickening and ground-glass opacity with a gravitational distribution in a patient with cardiogenic pulmonary edema. 62
Nodular Septal thickeningLymphangitic carcinomatosis :show diffuse smooth and nodularseptal thickening. Sarcoidosis : right lung base shows interlobular septal thickening associated with several septal nodules giving beaded appearanceFocal septal thickening inlymphangitic carcinomatosis 63
Intralobular interstitial thickening (Intralobular lines)• Results in a fine reticular pattern on HRCT, with the visible lines separated by a few millimeters• Fine lace- or netlike appearance• Causes : Pulmonary fibrosis Asbestosis Chronic Eosinophilic pneumonitis. 64
PARENCHYMAL BANDS• Non tapering , reticular opacity usually 1 to 3 mm in thickness and from 2 to 5 cm in length.• Is often peripheral and generally contracts the pleural surface• D/D : 1. Asbestosis 2. Sarcoidosis 3. Silicosis/ coal worker pneumoconiosis 4. Tuberculosis with associated scarring. 65
Subpleural Interstitial Thickening• Mimic thickening of fissure.• DD similar to that of interlobular septal thickening.• more common than septal thickening in IPF or UIP of any cause. 66
HONEYCOMBING• Defined as - small cystic spaces with irregularly thickened walls composed of fibrous tissue.• Predominate in the peripheral and subpleural lung regions• Subpleural honeycomb cysts typically occur in several contiguous layers. D/D- paraseptal emphysema in which subpleural cysts usually occur in a single layer.• Indicates the presence of ―END stage‖ disease regardless of the cause. 67
Nodules and Nodular Opacities Size, Distribution, Appearance Small Nodules: <10 mm Miliary - <3 mm Size Large Nodules: >10 mm Masses - >3 cms Interstitial opacity: Well-defined, homogenous, Soft-tissue density Obscures the edges of vessels or adjacent structure Appearance Air space: Ill-defined, inhomogeneous. Less dense than adjacent vessel – GGO small nodule is difficult to identify 69
Interstitial nodules Air space opacityMiliary tuberculosis in a lung transplant patient with bronchopneumonia 70 sarcoidosis
RANDOM: no consistent relationship to any structuresDistribution CENTRILOBULAR: related to centrilobular structures PERILYMPHATIC: corresponds to distribution of lymphatics 71
Perilymphatic distributionNodules in relation to pulmonary lymphatics at # perihilar peribronchovascular interstitium, # interlobular septa, # subpleural regions, and # centrilobular interstitium. 72
Centrilobular nodules• Distributed primarily within the centre of the secondary pulmonary lobule• Reflect the presence of either interstitial or airspace abnormalities• Dense or ground-glass opacity• Subpleural lung is typically spared- distinguishes fromdiffuse random nodules. 74
Tree-in-bud Centrilobular nodules m/b further characterized by presence or absence of ‗‗tree-in-bud.‘‘ Tree-in-bud -- Impaction of centrilobular bronchus with mucous, pus, or fluid, resulting in dilation of the bronchus, with associated peribronchiolar inflammation . Dilated, impacted bronchi produce Y- or V-shaped structures This finding is almost always seen with pulmonary infections. 75
Centrilobular nodules with or without tree-in-bud opacity: D/D : With tree-in-bud opacity Without tree-in-bud opacity Bacterial pneumonia All causes of centrilobular Typical and atypical nodules with tree-in-bud mycobacteria infections opacity Bronchiolitis Hypersensitivity Diffuse panbronchiolitis pneumonitis Aspiration Respiratory bronchiolitis Allergic bronchopulmonary Cryptogenic organizing aspergillosis pneumonia Cystic fibrosis Pneumoconioses Endobronchial-neoplasms Langerhans’ cell (particularly histiocytosis Bronchioloalveolar Pulmonary edema carcinoma) Vasculitis Pulmonary hypertension 77
Random nodules Random nodules – No definable distribution Are usually distributed uniformly throughout the lung parenchyma in a bilaterally symmetric distribution. Random nodules: Miliary tuberculosis. Axial HRCT image shows multiple nodules scattered uniformly throughout the lung parenchyma. 78
GROUND GLASS OPACITIES• Hazy increased attenuation of lung, with preservation of bronchial and vascular margins• Pathology : it is caused by # partial filling of air spaces, # interstitial thickening, # partial collapse of alveoli, # normal expiration, or # increased capillary blood volume• D/t volume averaging of morphological abnormality too small to be resolved 82 by HRCT
IMPORTANCE OF GGO• Can represent - microscopic interstitial disease(alveolar interstitium) - microscopic alveolar space disease - combination of both In the absence of fibrosis, mostly indicates the presence of an ongoing, active, potentially treatable process NB :: Ground Glass opacity should be diagnosed only on scans obtained with thin sections : with thicker sections volume averaging is more - leading to spurious GGO, regardless of the nature of abnormality 83
The location of the abnormalities in ground glass pattern can be helpful:• Upper zone predominance: Respiratory bronchiolitis PCP.• Lower zone predominance: UIP, NSIP, DIP.• Centrilobular distribution: Hypersensitivity pneumonitis, Respiratory bronchiolitis 85
GGO with few cystic and reticular lesion in HIV + ve patient -- PCPCombination of GGO withfibrosis and tractionalbronchiectasis-- NSIP 86
CRAZY PAVING PATTERN• It is scattered or diffuse ground-glass attenuation with superimposed interlobular septal thickening and intralobular lines.• Causes: 87
Combination of ground glassopacity and septal thickening: Alveolar proteinosis. 88
CONSOLIDATION• Consolidation is defined as increased attenuation, which results in obscuration of the underlying vasculature, usually producing air bronchogram.• The presence of consolidation implies that the air within affected alveoli has been replaced by another substance, such as blood, pus, oedema, or cells.• When consolidation is evident on a chest radiograph, HRCT does not usually provide additional diagnostically useful information. 89
D/D on the basis of presentationAcute consolidation is seen in: - Pneumonias (bacterial, mycoplasma , PCP) - Pulmonary edema due to heart failure or ARDS - Hemorrhage - Acute eosinophilic pneumoniaChronic consolidation is seen in: - Organizing Pneumonia - Chronic eosinophilic pneumonia - Fibrosis in UIP and NSIP - Bronchoalveolar carcinoma or lymphoma 90
Patchy ground-glass opacity, Peripheral consolidations withconsolidation, and nodule mainly with upper lobe predominance (photoperibronchovascular distribution with negative of pulmonary edema)reversed halo signs (central ground-glass opacity and surrounding air-spaceconsolidation) 91
High attenuation opacity• Talcosis asso with fibrotic mass,• inhalation of metals (tin/barium)Small focal areas of increased attenuation • injection and embolized radiodense materials such as mercury or acrylic cementDiffuse, increased lung attn in absence of calcification• amiodarone lung toxicity or• embolization of iodinated oil after chemoembolization 93
HRCT findings manifesting as decreased lungopacityLung Cysts,Emphysema,andBronchiectasis 95
Lung cysts • Thin walled (less than 3mm) , well defined and circumscribed air containing lesions • They are lined by cellular epithelium, usually fibrous or epithelial in nature. • Common cause are : 1. Lymphangiomyomatosis 2. Langerhans Histiocytosis 3. Lymphoid interstitial pneumonia They need to be differentiated from emphysematous bullae, blebs and pneumatocele. 96
Axial HRCT image through the upper lobes shows multiple bilateral uniform, thin-walled cysts.Axial HRCT image through the upperlobes shows multiple bilateral bizarre-shaped cysts and small centrilobularnodules in a smoker with Langerhans’cell histiocytosis. 97
BRONCHIEACTASISBronchiectasis is defined as localized, irreversible dilation of the bronchial tree.HRCT findings of the bronchiectasis include # Bronchial dilatation # Lack of bronchial tapering # Visualization of peripheral airways. 98
BRONCHIAL DILATATION # The broncho-arterial ratio (internal diameter of the bronchus /pulmonary artery) exceeds 1. # In cross section it appears as ―Signet Ring appearance‖ LACK OF BRONCHIAL TAPERING # The earliest sign of cylindrical bronchiectasis # One indication is lack of change in the size of an airway over 2 cm after branching. VISUALIZATION OF PERIPHERAL AIRWAYS # Visualization of an airway within 1 cm of the costal pleura is abnormal and indicates potential bronchiectasis 99
Coned axial HRCT image shows bronchialdilation with lack of tapering . Bronchialmorphology is consistent with varicosebronchiectasis. 100
A NUMBER OF ANCILLARY FINDINGS ARE ALSO RECOGNIZED: # Bronchial wall thickening : normally wall of bronchus should be less than half the width of the accompanying pulmonary artery branch. # Mucoid impaction # Air trapping and mosaic perfusionExtensive, bilateral mucoid impactionMosaic perfusion caused by large and small airway obstruction.Small centrilobular nodules are visible in the right lower lobe 101
Types1. CYLINDRICAL BRONCHIECTASIS # mildest form of this disease, # thick-walled bronchi that extend into the lung periphery and fail to show normal tapering2. VARICOSE BRONCHIECTASIS # beaded appearance of bronchial walls - dilated bronchi with areas of relative narrowing # string of pearls. # Traction bronchiectasis often appears varicose. 102
3. CYSTIC BRONCHIECTASIS : # Group or cluster of air-filled cysts, # cysts can also be fluid filled, giving the appearance of a cluster of grapes.4.TRACTION BRONCHIECTASIS : # Defined as dilatation of intralobular bronchioles because of surrounding fibrosis # due to fibrotic lung diseases 103
EMPHYSEMA• Permanent, abnormal enlargement of air spaces distal to the terminal bronchiole and accompanied by the destruction of the walls of the involved air spaces. 105
Centrilobular (proximal or centriacinar)emphysema • Found most commonly in the upper lobes • Manifests as multiple small areas of low attenuation without a perceptible wall, producing a punched-out appearance. • Often the centrilobular artery is visible within the centre of these lucencies. 106
PANLOBULAR EMPHYSEMA• Affects the entire secondary pulmonary lobule and is more pronounced in the lower zones• Complete destruction of the entire pulmonary lobule.• Results in an overall decrease in lung attenuation and a reduction in size of pulmonary vessels 107
Paraseptal (distal acinar) emphysema • Affects the peripheral parts of the secondary pulmonary lobule • Produces subpleural lucencies. 108
Cicatricial Emphysema/ irregular air spaceenlargement • previously known as irregular or cicatricial emphysema • can be seen in association with fibrosis • with silicosis and progressive massive fibrosis or sarcoidosis BULLOUS EMPHYSEMA : • Does not represent a specific histological abnormality • Emphysema characterized by large bullae • Often associated with centrilobular and paraseptal emphysema 109
Paraseptal Emphysema vs Honeycombing Paraseptal emphysema Honeycomb cysts occur in a single layer at the may occur in several layers in pleural surface the subpleural lung predominate in the upper lobes predominate at the lung bases unassociated with significant Asso with other findings of fibrosis fibrosis. Associated with other findings of Absent emphysema 110
Bullae A sharply demarcated area of emphysema ≥ 1 cm in diameter a thin epithelialized wall ≤ 1 mm. uncommon as isolated findings, except in the lung apices Usually asso with evidence of extensive centrilobular or paraseptal emphysema When emphysema is associated with predominant bullae, it may be termed bullous emphysema 111
Pneumatocele• Defined as a thin-walled, gas-filled space within the lung,• Associated with acute pneumonia or hydrocarbon aspiration.• Often transient.• believed to arise from lung necrosis and bronchiolar obstruction.• Mimics a lung cyst or bulla on HRCT and cannot be distinguished on the basis of HRCT findings. 112
CAVITARY NODULE• Thicker and more irregular walls than lung cysts• In diffuse lung diseases - LCH, TB, fungal infections, and Cavitary nodules or cysts in sarcoidosis. tracheobronchial papillomatosis.• Also seen in rheumatoid lung disease, septic embolism, pneumonia, metastati c tumor, tracheobronchial papillomatosis, and Wegener granulomatosis 113 fungal pneumonia
Mosaic attenuation & perfusion• Lung density and attenuation depends partially on amount of blood in lung tissue.• The term mosaic attenuation is used to describe density differences between affected and non-affected lung areas.• It is seen as inhomogeneous attenuation of lung parenchyma with focal region of lucency which show smaller size of vessels• May be due to vascular obstruction, abnormal ventilation or airway disease/ 114
Mosaic attenuation due to small airway disease # Air trapping and bronchial dilatation commonly seen. # Areas of increased attenuation have relatively large vessels, while areas of decreased attenuation have small vessels. # Causes include: Bronchiectasis, cystic fibrosis and bronchiolitis obliterans.Mosaic attenuation due to vascular disease # common in patients with acute or chronic pulmonaryembolism (CPE), and # decreased vessel size in less opaque regions is oftenvisible 115
MOSIAC PATTERN DEPENDENT LUNG ONLY NONDEPENDENT LUNG EXPIRATION PRONE POSITION NO AIR TRAPPING AIR NOT TRAPPING RESOLVE RESOLVE VESSEL SIZE PLATE GROUNDATELECTASIS GLASS AIRWAYS DECREASED NORMAL DISEASE GROUND VASCULAR GLASS 116
Inhomogeneous lung opacity: mosaic perfusion in a patient with bronchiectasis.central bronchiectasis with multifocal, bilateral inhomogeneous lung opacity.The vessels within the areas of abnormally low attenuation are smaller than their counterparts in areas of normal lung attenuation. 117
Air trapping on expiration • Most patients with air trapping seen on expiratory scans have inspiratory scan abnormalities, such as bronchiectasis, mosaic perfusion, airway thickening, or nodules suggest the proper differential diagnosis. • Occasionally, air trapping may be the sole abnormal finding on an HRCT study. • The differential diagnosis include --- bronchiolitis obliterans; asthma; chronic bronchitis; and hypersensitivity pneumonitis 118
Air trapping on expiratory imaging in the absence of inspiratory scan findings in a patient with bronchiolitis obliterans.(A) Axial inspiratory image through the lower lobes shows no clear evidence of inhomogeneous lung opacity.(B) Axial expiratory image shows abnormal low attenuation (arrows) caused by air trapping, representing failure of the expected increase in lung attenuation that should normally occur with expiratory imaging. 119
Head cheese sign• It refers to mixed densities which includes presence of- # consolidation # ground glass opacities # normal lung # Mosaic perfusion• Signifies mixed infiltrative and obstructive disease• Common cause are : Hypersensitive pneumonitis Sarcoidosis DIP 120
Axial HRCT image in a patient withhypersensitivity pneumonitis shows acombination of ground-glass opacity, normallung, and mosaic perfusion (arrow) on the sameinspiratory image. 121
Distribution within the lungUpper lung zone preference is seen in: 1.Inhaled particles: pneumoconiosis (silica orcoal) 2.Smoking related diseases (centrilobularemphysema 3. Respiratory bronchiolitis (RB-ILD) 4.Langerhans cell histiocytosis 5.Hypersensitivity pneumonitis 6.SarcoidosisLower zone preference is seen in: 1. UIP 2. Aspiration 3. Pulmonary edema 122
Central vs peripheral zone• Central Zone Peripheral zone 1. Sarcoidosis 1. COP 2. Cardiogenic pulmonary 2. Ch Eosinophilic Pneumonia edema 3. UIP 3. Bronchitis 4. Hematogenous mets 123
Additional findingsPleural effusion is seen in:• Pulmonary edema• Lymphangitic spread of carcinoma - often unilateral• Tuberculosis• Lymphangiomyomatosis (LAM)• Asbestosis 124
Hilar and mediastinal lymphadenopathy # In sarcoidosis the common pattern is right paratracheal and bilateral hilar adenopathy (1-2-3-sign). # In lung carcinoma and lymphangitic carcinomatosis adenopathy is usually unilateral. #Eggshell calcification in lymph nodes occurs in ---- Silicosis and coal-workers pneumoconiosis and is sometimes seen in sarcoidosis, post irradiation Hodgkin disease, blastomycosis and scleroderma . 125
Conclusion • A thorough knowledge of the basic anatomy is of utmost importance. When attempting to reach a diagnosis or differential diagnosis of lung disease using HRCT, the overall distribution of pulmonary abnormalities should be considered along with their morphology, HRCT appearance, and distribution relative to lobular structures. Correlation of the radiological findings with patients clinical and laboratory findings to reach a likely diagnosis 126