HRCT PATTERNS

Secondary lobule

• It is the basic anatomic unit of pulmonary structure and function.

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It is the smallest lung unit that is surrounded by connective tissue septa.

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

Raoof, S. , CHEST 2006; 129:805

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terminal bronchioles

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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

Increased attenuationDecreased attenuation

interlobular septal thickening

Irregular smooth nodularLung distortion

Honey lymphangitic tumor

Combing DDs sarcoidosis Sarcoidosis,asbestosis

smooth

Thick septa predominant ground glass predominant

Lymphangitic tumor crazy paving DDs

Pulm oedemaHaemorrhageAmyloid(rare)

Peribronchovascular interstitial thickening

Lymphangitic spread of carcinomaLymphomaLeukaemiaLIPInterstitial edemaSarcoidosis

Interlobular septal thickening

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).

Nodular septal thickening

Parenchymal bands

Non tapering reticular opacity,1-3 mm in tickness and 2 to 5 cm in length

Often peripheral and contacts the pleural surface

Represent contiguous thickened interlobulsr septa,peribronchovascular fibrosis,scars or atelectasis

DD’S

AsbestosisSarcoidosisSilicosisTB

Subpleural line

Curvilinear opacity,few mm or les in thickness,prallelling the pleura and less than 1 cm from the pleural surface.

Represent fibrosis / localized alveolar collapse / atelectasis.

Commonly seen in asbestosis

Size, Distribution, AppearanceNodules and Nodular Opacities

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SizeSize

Small Nodules: <10 mm Micro - <3 mmSmall Nodules: <10 mm Micro - <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

Based on distribution

Perilymphatic

Centrilobular

Random

Sarcoidosis

The majority of nodules located along the bronchovascular bundle (yellow arrow).

Centrilobular nodules

5 to 10mm away from the pleural surfaceEvenly spacedAssociated with pumonary artery branchesIf air filled centrilobular bronchiole----lucency

within the nodule

Causes

Bronchiolar and peribronchiolarVascular and perivascular

Bronchiolar and peribronchiolar

Endobronchiolar spreadHSPBronchiolitis obliteransRespiratory bronchiolitisCystic fibrosisBronchiectasis

Vascular and perivascular

Pulmonary edemaVasculitisPulmonary hemorrhagePulm HTN

Tree-in-bud

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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.

Tree-in-bud

Typical Tree-in-bud appearance in a patient with active TB.

Random nodules

Hematogenous metsMiliary TBMiliary fungal infectionsSarcoidosis ( extensive)LCH

Langerhans cell histiocytosis: early nodular stage before the typical cysts appear.

Parenchymal opacification

GGOConsolidationLung calcification and high attenuation

opacities

Ground glass opacity

Hazy increase in lung opacity not associated with obscuration of underlying vessels or bronchial margins

Significance of GGO

Acute symptoms---asociation with active disease

Subaute or chronic---active disease / fibrosis

Crazy paving pattern

Superimposition of reticular pattern on GGOPAPAcute silicosisPulmonary edemaPulmonary haemorrhageARDSP.Carnii pneumonias

Consolidation

Increased lung attenuation with obscuration of underlying vessels

Lung calcification and high attenuation opacities

Multifocal calcification (often with nodules) T.B, Histoplasmosis, varicella pneumonia,

sarcoidosisDiffuse and dense calcification Metastatic calcification (due to

hypercalcemia ,in patients with CRF, Hyperparathyroidism) – calcification mainly interstitial.

Disseminated pulmonary ossification Alveolar microlithiasis (posterior and lower

lobe predominance

Low attenuation

Lung cysts,emphysema and bronchiectasis

Honey combingLung cystsEmphysemaBullaePneumatocoelesCavitary nodulesBronchiectasis

HONEYCOMBING67

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.

Honey combing

Air filled cystic spacesSeveral mm to cms in diameterPeripheral and subpleuralDefinable walls,1 to 3 mm in thicknessAssociated with findings of lung fibrosis

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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

Honeycombing

Typical UIP pattern with in a patient with idiopathic pulmonary fibrosis

Lung cysts

Well defined rounded or circumscribed lesion with a wall that may be uniform or varied in thickness ( < 2-3 mm)

LAMLCHLIPBullaePneumatocoelesHoneycombingCystic bronchiectasis

Langerhans cell histiocytosis

HRCT Appearances LAM

Numerous thin-walled cysts, surrounded by normal parenchyma. Round in shape and more or less uniform.

Mediastinal or hilar adenopathy .Chylous Pleural effusions (40%).Recurrent pneumothorax (40%)

Multiple thin-walled cysts of roughly uniform

size.

Unlike LCH, the cysts in LAM tend to be

rounded and uniformly distributed throughout

the parenchyma with no regional sparing.

There is a conspicuous absence of nodules.

Lymphangiomyomatosis complicated by pneumothorax

Emphysema

Permanent abnormal enlargement of air spaces distal to terminal bronchiole accompanied by destruction of walls of involved air spaces

CentrilobularParaseptalPanlobularIrregular / cicatricalBullous

Centrilobular emphysema Most common type Upper lobe predominance Strongly associated with smoking.

Centrilobular emphysema 81

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.

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

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Panlobular emphysema

Paraseptal (distal acinar) emphysema86

Affects the peripheral parts of the secondary pulmonary lobule

Produces subpleural lucencies.

Paraseptal emphysema

Paraseptal emphysema v/s honeycombing

Centrilobular emphysema and lung cysts

Bullae and blebs

Bulla : sharply demarcated area of emphysema measuring 1cm or more in diameter with a wall that is < 1 mm.

Bleb: focal thin walled lucency contigous with pleura usually at lung apex

Pneumatocoele

Thin walled gas filled space within the lung,usually assosciated with pneumonia

Appearance similar to cyst or bulla and cannot be differentiated

Cavitary nodules

• Thicker and irregular walls than cysts• LCH• TB• Fungal infections• Sarcoidosis• Rheumatoid lung disease• Mets• wegeners

Bronchiectasis

Localized irrevesible bronchial dilatation with thickening of the bronchial wall.

CylindricalVaricoseCysticTraction

• 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

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

Mosaic perfusion and attenuation

Due to airway diseaseDue to vascular diseaseInfiltrative process adjacent to normal lung

Inhomogenous lung opacity

Decreased vessel size Uniform sized vessels

Some regions too lucent Some regions too dense

No reticulation Associated reticulation,

No Nodules Nodules

Mosaic perfusion Ground glass opacity

Inhomogenous lung opacity

Decreased size of vessels uniform sized vessels

(suspect mosaic perfusion) (suspect GGO)

No air trapping air trapping no air trapping

Vascular disease obstructive disease infiltrative disease

Chronic PE small airways disease GGO DD’s

large airways disease

Air trapping on expiration

Diagnosis of air trapping in obstructive lung disease

Diagnosis of airway diseases with normal inspiratory scan

Distinguishing mosaic perfusion from GGOAllowing the diagnosis of mixed infiltrative

and obstructive diseases

Nodular pattern

1.Hypersensitivity pneumonitis:2.Miliary TB: random nodules 3.Sarcoidosis4.Hypersensitivity pneumonitis

Low Attenuation pattern

Lymphangiomyomatosis (LAM)LCH

Honeycombing Centrilobular emphysema

Thank you

Mosaic perfusion

Pulmonary hypertension Abnormal airwaysLarge areas of lucency Lobular lucencies

Vascular disease Obstructive disease

Chronic PE small airways disease

lareg airways disease