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HRCT
DR Shahid Pervaiz
Post Graduate trainee
Dept. Of Pumonology
Nishtar Hospital Multan
INTRODUCTIONINTRODUCTION
• 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.
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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.
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.
There are approximately 23 generation of dichotomous branchingFrom trachea to the alveolar sac
HRCT can identify upto 8th order central bronchioles
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SUBJECTS
Anatomy of the secondary lobule
Basic HRCT patterns
Distribution of abnormalities
Differential diagnosis of interstitial lung diseases
Secondary lobule
• The secondary lobule is the basic anatomic unit of pulmonary structure and function.Interpretation of interstitial lung diseases is based on the type of involvement of the secondary lobule.It is the smallest lung unit that is surrounded by connective tissue septa.It measures about 1-2 cm and is made up of 5-15 pulmonary acini, that contain the alveoli for gas exchange.
Secondary lobuleBasic anatomic unit of pulmonary structure and function.
1-2 cm and is made up of 5-15 pulmonary acini
Supplied by a small bronchiole (terminal bronchiole) in the center, that is parallelled by the centrilobular artery.
Pulmonary veins and lymphatics run in the periphery
Two lymphatic systems: central network peripheral network
• The secondary lobule is supplied by a small bronchiole (terminal bronchiole) in the center, that is parallelled by the centrilobular artery. Pulmonary veins and lymphatics run in the periphery of the lobule within the interlobular septa.Under normal conditions only a few of these very thin septa will be seen.
There are two lymphatic systems: a central network, that runs along the bronchovascular bundle towards the centre of the lobule and a peripheral network, that is located within the interlobular septa and along the pleural linings.
The terminal bronchiole in the center divides into respiratory bronchioli with acini that contain alveoli. Lymphatics and veins run within the interlobular septa
Centrilobular area
It is the central part of the secondary lobule.It is usually the site of diseases, that enter the lung through the airways ( i.e. hypersensitivity pneumonitis, respiratory bronchiolitis, centrilobular emphysema ).
Centrilobular area in blue perilymphatic area in yellow
Perilymphatic area
Perilymphatic areais the peripheral part of the secundary lobule.It is usually the site of diseases, that are located in the lymphatics of in the interlobular septa ( i.e. sarcoid, lymphangitic carcinomatosis, pulmonary edema). These diseases are usually also located in the central network of lymphatics that surround the bronchovascular bundle.
Raoof, S. , CHEST 2006; 129:805
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A group of terminal bronchioles
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Unit of lung (0.5-3 cm)Irregularly polyhedral Supplied by a group of terminal bronchioles and accompanying pulmonary arterioles surrounded by lymph vesselsDemarcated by “interlobular septa”
pulmonary veinspulmonary lymphaticsconnective tissue stroma
Accompanying pulmonary arterioles
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Surrounded by lymph vessels
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Pulmonary veins
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Pulmonary lymphatics
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Connective Tissue StromaConnective Tissue Stroma
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Perilymphatic distribution
Centrilobular distribution
Random distribution
DOTSss.....
TO SUM UP..
• Random – touch pleura – scattered in lung
• Centrilobular –away from pleura
• Perilymphatic – around vessels, bronchi – touch pleura or fissure
Size, Distribution, Appearance
Nodules and Nodular Opacities
SizeSize
Small Nodules: <10 mm Miliary - <3 mmSmall Nodules: <10 mm Miliary - <3 mm
Large Nodules: >10 mm Masses - >3 cmsLarge Nodules: >10 mm Masses - >3 cms
AppearanceAppearance
Interstitial opacity: Well-defined, homogenous,Soft-tissue densityObscures the edges of vessels or adjacent structure
Interstitial opacity: Well-defined, homogenous,Soft-tissue densityObscures the edges of vessels or adjacent structure
Air space: Ill-defined, inhomogeneous.Less dense than adjacent vessel – GGOsmall nodule is difficult to identify
Air space: Ill-defined, inhomogeneous.Less dense than adjacent vessel – GGOsmall nodule is difficult to identify
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Interstitial nodules
Air space opacity
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Miliary tuberculosis
sarcoidosis
in a lung transplant patient with bronchopneumonia
RANDOM: no consistent relationship to any structuresRANDOM: no consistent relationship to any structures
PERILYMPHATIC: corresponds to distribution of lymphaticsPERILYMPHATIC: corresponds to distribution of lymphatics
CENTRILOBULAR: related to centrilobular structuresCENTRILOBULAR: related to centrilobular structuresDistributionDistribution
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Reticular patternIn the reticular pattern there are too many lines, either as a result of thickening of the interlobular septa or as a result of fibrosis as in honeycombing.
Focal septal thickening in lymphangitic carcinomatosis
Septal thickening and ground-glass opacity with a gravitational distribution in a patient with cardiogenic pulmonary edema.
Notice the nodules along the fissures indicating a perilymphatic distribution (red arrows).
The majority of nodules located along the bronchovascular bundle (yellow arrow).
Sarcoidosis
The majority of nodules located along the bronchovascular bundle (yellow arrow).
PERILYMPHATIC NODULES
Perilymphatic and Random
distribution of nodules , seen in
sarcoidosis.
Centrilobular distribution
Hypersensitivity pneumonitis Respiratory bronchiolitis in smokers infectious airways diseases (endobronchial spread of tuberculosis or nontuberculous mycobacteria, bronchopneumonia) Uncommon in bronchioloalveolar carcinoma, pulmonary edema, vasculitis
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.
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Tree-in-budTree-in-bud describes the appearance of an irregular and often nodular branching structure, most easily identified in the lung periphery.
Typical Tree-in-bud appearance in a patient with active TB.
Random distribution
Small random nodules are seen in: Hematogenous metastases
Miliary tuberculosis
Miliary fungal infections
Sarcoidosis may mimick this pattern, when very extensive
Langerhans cell histiocytosis (early nodular stage)
Langerhans cell histiocytosis: early nodular stage before the typical cysts appear.
Attenuation pattern
High Attenuation pattern
GROUND GLASS CONSOLIDATION
Low Attenuation pattern
Emphysema Lung cysts (LAM, LIP, Langerhans cell histiocytosis) Bronchiectasis Honeycombing
Dark bronchus sign in ground glass opacity. Complete obscuration of vessels in consolidation.
Ground-glass opacity
Broncho-alveolar cell carcinoma with ground-glass opacity and consolidation
Consolidation
Two patients with chronic consolidations as a result of COP (cryptogenic organizing pneumonia)
Mosaic attenuationThe term 'mosaic attenuation' is used to describe density differences between affected and non-affected lung areas.
Mosaic attenuation
Lung density and attenuation depends partially on amount of blood in lung tissue.
May be due to vascular obstruction, abnormal ventilation or airway disease
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Mosaic pattern in a patient with hypersensitivity pneumonitis
Mosaic pattern in a patient with chronic thromboemboli
Crazy Paving PatternCrazy Paving is a combination of ground glass opacity with
superimposed septal thickening
Crazy Paving can be seen in: Alveolar proteinosis Sarcoid NSIP Organizing pneumonia (COP/BOOP) Infection (PCP, viral, Mycoplasma, bacterial) Neoplasm (Bronchoalveolarca (BAC) Pulmonary hemorrhage Edema (heart failure, ARDS, AIP)
CRAZY PAVING PATTERNIt is scattered or diffuse ground-glass attenuation with superimposed interlobular septal thickening and intralobular lines.
Causes:
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Crazy Paving in a patient with Alveolar proteinosis.
Crazy Paving
Combination of ground glass opacity and septal thickening : Alveolar proteinosis.
Combination of ground glass opacity and septal thickening : Alveolar proteinosis
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Head cheese signIt refers to mixed densities which includes
# consolidation # ground glass
opacities # normal lung # Mosaic perfusion
• Signifies mixed infiltrative and obstructive disease
Head cheese signCommon cause are :
1. Hypersensitive pneumonitis
2. Sarcoidosis
3. DIP
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Headcheese sign
Headcheese sign in hypersensitivity pneumonitis.
HRCT scan shows lung with a geographic appearance, which represents a combination of patchy or lobular ground-glass opacity (small arrows) and mosaic perfusion (large arrows).
Low Attenuation pattern
Emphysema
Lung cysts (LAM, LIP, Langerhans cell histiocytosis)
Bronchiectasis
Honeycombing
Emphysema
Emphysema typically presents as areas of low attenuation without visible walls as a result of parenchymal destruction.
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.
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Centrilobular emphysema Most common type Irreversible destruction of alveolar walls
in the centrilobular portion of the lobule Upper lobe predominance and uneven
distribution Strongly associated with smoking.
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.
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Centrilobular emphysema due to smoking. The periphery of the lung is spared (blue arrows). Centrilobular artery (yellow arrows) is seen in the center of the hypodense area.
Panlobular emphysema Affects the whole secondary lobule Lower lobe predominance In alpha-1-antitrypsin deficiency, but
also seen in smokers with advanced emphysema
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
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PANLOBULAR EMPHYSEMA
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Panlobular emphysema
Paraseptal (distal acinar) emphysema
Affects the peripheral parts of the secondary pulmonary lobule
Produces subpleural lucencies.
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Paraseptal emphysema
Cystic lung disease
Lung cysts are defined as radiolucent areas with a wall thickness of less than 4mm.
Langerhans cell histiocytosis
Lymphangiomyomatosis complicated by pneumothorax
Bronchiectasis
Bronchiectasis is defined as localized bronchial dilatation. (signet-ring sign)
bronchial wall thickening
lack of normal tapering with visibility of airways in the peripheral lung
mucus retention in the broncial lumen
associated atelectasis and sometimes air trapping
ABPA: glove-finger shadow due to mucoid impaction in central bronchiectasis in a patient with asthma.
Signet-Ring Sign
A signet-ring sign represents an axial cut of a dilated bronchus (ring) with its accompanying small artery (signet).
Tram Tracks
Bronchial dilation with lack of tapering .
HONEYCOMBINGDefined 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.
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HoneycombingHoneycombing is defined by the presence of small cystic spaces with irregularly thickened walls composed of fibrous tissue.
Causes
Lower lobe predominance : 1. UIP or interstitial fibrosis 2. Connective tissue disorders 3. Hypersensitivity pneumonitis 4. Asbestosis 5. NSIP (rare)
Upper lobe predominance : 1. End stage sarcodosis 2. Radiation 3. Hypersensitivity Pneumonitis 4. End stage ARDS
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Honeycombing
HRCT showing subpleural broncheolectasis
Honeycombing and traction bronchiectasis in UIP.
Typical UIP with honeycombing and traction bronchiectasis in a patient with idiopathic pulmonary fibrosis (IPF)
Distribution within the lung
Additional findings
Differential diagnosis of interstitial lung diseases
Reticular pattern
Nodular pattern
High Attenuation pattern
Low Attenuation pattern
Lymphangitic carcinomatosis: irregular septal thickening, usually focal or unilateral 50% adenopathy', known carcinoma.
Cardiogenic pulmonary edema: incidental finding in HRCT, smooth septal thickening with basal predominance (Kerley B lines), ground-glass opacity with a gravitational and perihilar distribution, (peribronchial cuffing)
Cardiogenic pulmonary edema
Lymphangitic carcinomatosis
Lymphangitic carcinomatosis with hilar adenopathy
Nodular pattern
1.Hypersensitivity pneumonitis:2.Miliary TB: random nodules 3.Sarcoidosis4.Hypersensitivity pneumonitis
Nodular pattern
Hypersensitivity pneumonitis Miliary TB
Sarcoidosis Hypersensitivity pneumonitis
Low Attenuation pattern
Lymphangiomyomatosis (LAM) LCH
Honeycombing Centrilobular emphysema
Low Attenuation pattern (2)
Centrilobular emphysema: Langerhans cell histiocytosis (LCH)
Honeycombing. Lymphangiomyomatosis (LAM)
Q.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) ?
STRUCTURED APPROACH
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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
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THANK YOU