Interstitial Lung Disease.pptx

Outline
Introduction
• Definition
• Classification
• Anatomy
• Pathophysiology
Radiological Findings in CXR
Radiological Findings in HRCT

INTRODUCTION
Interstitial lung disease (ILD) is A heterogeneous
group of non-neoplastic disorders resulting from
damage to the lung parenchyma by inﬂammation
and ﬁbrosis that diminish the lung’s capacity for
alveolar gas diffusion.
Interstitial lung diseases classically produce the
clubbing of the nails, and coarse crackles on

Precipitating Factors
A number of precipitants can cause diffuse interstitial
disease such as:
• smoking,
• organic dusts (causing hypersensitivity pneumonitis),
• inorganic dusts (causing pneumoconioses),
• gases or fumes,
• drugs,
• radiation,
• infection.

ILD
Meyer, K. C., An Overview of the Classification and Diagnosis of Interstitial Lung Disease. In Clinical Handbook of Interstitial Lung Disease. CRC Press, 2018
Etiology

ILD
Meyer, K. C., An Overview of the Classification and Diagnosis of Interstitial Lung Disease. In Clinical Handbook of Interstitial Lung Disease. CRC Press, 2018

Classification ofILD
Travis WD, et al. An ofﬁcial ATS/ERS Statement: Update of the International Multidisciplinary Classiﬁcation of the Idiopathic Interstitial Pneumonias. Am J Respir Crit Care Med, 2013

AnatomyofRespiratorySystem
Structurally, consists of two
parts:
(1)The upper respiratory
system: the nose, nasal cavity,
pharynx, and associated
structures;
(2)The lower respiratory system:
the larynx, trachea, bronchi, and
lungs.
Brashers, V. L., Structure and Function of the Pulmonary System. In Pathophysiology - The Biologic Basis for Disease in Adults and Children, 8th ed.; Elsevier: 2019;

Functionally, consists of two parts:
(1) The conducting zone
(2) The respiratory zone

Carter, B. W., Interstitial Network. In Imaging Anatomy: Chest,Abdomen, Pelvis, 2nd ed. Elsevier: Philadelphia, 2017.
PulmonaryInterstitium
= Continuum of loose connective tissue, extends from pulmonary hila to visceral
pleura
3 Subdivisions forming continuum:
1)Axial (Peribronchovascular /
Bronchoarterial): surrounding the
bronchi, arteries, and veins from the
lung root to the level of the respiratory
bronchiole.
2) Parenchymal (Intralobular and
alveolar septal): between the alveolar
and capillary basement membranes.
3) Peripheral (subpleural and
interlobular septal)
Components:
1) Matrix components: Collagen & elastin fibers
2) Cellular components: Fibroblasts, mast cells, tissue
macrophages, lymphocytes
3) Continuous epithelial and endothelial basement membranes  Form
barriers defining outer borders of interstitium

Pathophysiology ofILD
Bagnato, G., Cellular Interactions in the Pathogenesis of Interstitial Lung Diseases.Eur Respir Rev 2015
Wound healing and fibrosis are complex, involving
numerous cellular processes and molecular pathways (eg,
cell adhesion, migration, proliferation, apoptosis, etc.)
 Injury to the distal airspaces (eg, infection, radiation, environmental exposures) 
damage to the epithelial/endothelial layers and basement membrane.
 Structural remodeling of the distal airspaces  impaired gas exchange.
• In the past: result from persistent inflammation
• Recent paradigm: result from tissue injury with aberrant wound healing, 
resulting in collagenous fibrosis.

PathophysiologyofILD
https://www.pulmonaryfibrosis360.com/pulmonary-fibrosis-ilds (c) 2019Boehringer Ingelheim International GmbH

Radiological Findings in Chest X-
Ray (CXR)
Basic Patterns:
a. Linear/Septal
b. Reticular
c. Nodular
d. Reticulonodular
e. Consolidation
CXR: Usually the initial imaging test performed, relatively
inexpensive, easy to obtain and perform, but insufficient to
establish a definitive radiologic diagnosis.

A.CXR–Linear/SeptalPattern
Webb, R. W., Thoracic Imaging: Pulmonary and Cardiovascular Radiology, 3rd ed.; Wolters Kluwer: 2017
Linear opacities: mostly due to thickened interlobular septa.
 Appear as thin linear opacities between lobules;
 They are not usually seen in the healthy lung (normal septa: ±0.1 mm
thick)
but are clearly visible when thickened.
1. Kerley A lines: radiate from the hilum into the lung periphery preferentially
towards
the upper lobes.  represent thickening of the axial pulmonary interstitium.
2. Kerley B lines: predilection in the lower lung zones abutting a pleural surface. 
represent thickening of the subpleural interstitium.

A. CXR–Linear/SeptalPattern
Kerley’s A lines.
Thin oblique lines in
the parahilar lung
(arrows) represent A
lines.
Kerley’s B lines.
Thin horizontal lines
in the lung
periphery, (arrows).
Causes of Kerley Lines on CXR:
• Pulmonary edema
• Pneumoconiosis
• Sarcoidosis
• Interstitial Pulmonary Fibrosis from any cause
(rarely)

B.CXR–Reticular Pattern
= Collection of innumerable small linear opacities, produce an
appearance
resembling a net.
 Multiple intersecting lines, often irregular, outlining what appear to be
round or irregular “spaces” .
 Subdivided into three sub patterns:
1) Fine pattern (“spaces” < 3 mm)
2) Medium pattern (“spaces” 3 – 10 mm)
3) Coarse pattern (“spaces” > 10 mm).
Medium or coarse patterns: the most common and the most easily seen on CXR

Fine reticular pattern with poor definition of pulmonary
arteries in Langerhans Cell Histiocytosis (LCH)
1) Fine
Reticular

Medium reticular pattern in patient
with rheumatoid lung disease.
2) Medium
Reticular
Medium to coarse reticular pattern with a
predominant bibasilar and subpleural
distribution in end-stage lung fibrosis.

2) Medium Reticular
 A medium reticular pattern is typical of patients with pulmonary fibrosis
and “honeycombing”
Honeycombing : closely approximated ring shadows, typically 3–10 mm in diameter
with walls 1–3 mm in thickness, that resemble a honeycomb.
 Subsequent small cyst formation surrounded by fibrotic tissue.
 Relatively uniform in size and bunched together in grape-like clusters.
 forms an array of multilayered stacked spaces, are not separated by intervening normal lung.
 Have slightly thicker walls than emphysematous spaces.

Honeycombing
“Honeycomb”pattern in Idiopathic Interstitial Fibrosis.
“Honeycombing”is dependable radiographic sign of
interstitial fibrosis.
Medium to coarse reticular with honeycombing,
in a predominantly bibasilar and
subpleural distribution. Lung volumes are
decreased

Coarse reticular pattern in cystic lung disease.
Coned-down view of the right apex shows reticular
opacities outlining spaces exceeding 1 cm.
3) Coarse
Reticular

C.CXR–Nodular Pattern
= Innumerable small rounded opacities, range in diameter from 2-10 mm.
The distribution is widespread but not necessarily uniform.
 May indicate interstitial or air-space disease.
 Interstitial nodules: sharply marginated, despite being very small.
Miliary pattern: diffuse/widespread, well-defined nodules, diameter ≤2-3
mm. Miliary nodules are interstitial.
 Air-space or acinar nodules: typically, 5 to 10 mm in diameter,
poorly
marginated.

C.CXR–Nodular Pattern
Multiple noncalcified micronodules throughout both
lungs in Coal Worker’s Pneumoconiosis
Stark, P., Evaluation of DiffuseLung Disease by Conventional Chest Radiography; UpToDate: 2019
Silicosis.
Multiple nodules, 3 – 5 mm in diameter, with a bias for the
upper lobes. Note calcification in some of the pulmonary
nodules and the hilar lymph nodes.

C. CXR –Nodular Pattern
Diffuse bilateral small nodular opacities of the lungs (miliary pattern) on
CXR
Hansell, D. M. et al., Imaging Diseases of the Chest, Mosby Elsevier: 2010.

D.CXR–Reticulonodular Pattern
= A combined reticular and nodular pattern.
Indicating a perceived combination of lines and
dots.
Berylliosis.
Diffuse reticulonodular pattern throughout
both lungs, with relative sparing of the
apices and bases.
Lymphangioleiomyomatosis.
A typical example in a middle-aged woman
showing lower zone predominant
reticulonodular opacities and low, flat
hemidiaphragms.

D. CXR –Reticulonodular Pattern
Causes of Diffuse Bilateral Reticulonodular
Opacities

D. CXR –Reticulonodular Pattern
Signs that limit the differential diagnosis
of diffuse bilateral reticulonodular
opacities of the lungs on CXR

E.CXR–Consolidation Pattern
 Consolidation: Exudate or product of disease (water, blood, pus, cells,
or other substances) that replaces alveolar air, rendering the lung solid.
On CXR:
 Homogeneous opacities associated with obscuration of the pulmonary
vessels.
 Little / no loss of volume.
 Air bronchogram may be present.
• May occasionally result from encroachment of the airspaces by
extensive interstitial disease (e.g., sarcoidosis)
• ILD such as Acute Interstitial Pneumonia(AIP) and Cryptogenic
Organizing
Pneumonia (COP) have a major airspace component.

E.CXR–Consolidation Pattern
Parenchymal consolidation in
sarcoidosis. Bilateral areas of
consolidation in the middle and
upper lung zones.
Consolidation in AIP: (A) CXR is within normal
limits (B) CXR 11 months later, when the
patient developed acute shortness of breath,
shows extensive bilateral consolidation.
Chung, J. H.; Walker, C. M., Muller's Imaging of the Chest, 2nd ed.; Elsevier: Philadelphia, 2019.
COP: CXR shows
bilateral multifocal and confluent
consolidation involving mainly the
upper lobes.

 The correlation between the radiographic pattern and the stage of
disease is generally poor.
 Only honeycombing correlates with pathologic findings (portends a poor
prognosis).
 CXR is normal in ±10% of patients with some forms of ILD.
 A complete evaluation should be undertaken even if a symptomatic
patient has a normal CXR / an asymptomatic patient has
radiographic evidence of ILD.
Radiological Findings of ILD in CXR
Failure to adequately evaluate lead to disease progression that is
irreversible.

Radiological Findings of ILD in
HRCT
Basic Patterns:
a. Reticular
b. Nodular
c. Increased Attenuation
d. Decreased Attenuation
HRCT: Play a key role in the different stages of ILD,
essential for reaching positive and etiological
diagnoses, based on recognition of the pattern and
distribution of abnormalities.

HRCT –AnatomicalAspect
 A pulmonary lobule: marginated by connective
tissue interlobular septa (contain pulmonary v.
and lymphatics)
 The central portion of the secondary lobule
(centrilobular): contains the pulmonary artery
and bronchiole.
 The pulmonary artery can be seen in normal
lungs as a dot / branching structure 5 –10 mm
from the pleural surface; the centrilobular
bronchiole is normally invisible.

VisibilityofNormalStructuresonHRCT
 The smallest objects that can be resolved on HRCT range from 100 - 400 µm.
 The limits of spatial resolution determine the anatomy that can be identified on HRCT.

A.HRCT –Reticular Pattern
Morphologic variations:
1) Interlobular Septal Thickening
2) Honeycombing
3) Intralobular Reticulations

Smooth thickening of numerous septa in the right lung.
The thickened septa outline lobules of characteristic size
and shape. Centrilobular arteries (arrows) are visible
within many of the lobules.
1) Interlobular Septal
Thickening
Causes: infiltration of interlobular septal with fibrosis, abnormal cells, and
fluid.
Characteristics:
 Thin linear opacities between lobules
 Length of lines: 10 – 20 mm
 Preferential location: subpleural
 Presentation: simple lines / polygons

1) Interlobular Septal
Thickening
Differential Diagnoses of Septal Thickening

2) Honeycombing
Reflects extensive lung fibrosis with alveolar destruction / complete loss of acinar
architecture  results in a characteristic reticular appearance.
Necessary findings :
 Air-filled (i.e., black) cysts.
 The cysts have a thick (easily
recognizable) wall
 The cysts are usually from 2 – 10
mm in diameter.
 Cysts are immediately beneath the
pleural surface.
 Cysts share walls
Scattered isolated cysts are not sufficient.
Ferretti, G.; Imaging Atlas of Interstitial Lung Disease.. Boehringer Ingelheim International: 2019.

2) Honeycombing
Refl
= CT feature of established pulmonary
fibrosis.
 the term should be used with care, as it
may directly
impact patient care.

2) Honeycombing
Differential Diagnoses of Honeycombing
Akira, M. Radiographic Differentiation of Advanced Fibrocystic Lung Diseases. Annals ATS: 2017.

Traction Bronchiectasis /
Bronchiolectasis
= Represent irregular bronchial and bronchiolar dilatation caused by surrounding
retractile pulmonary fibrosis.
Characteristics:
 Irregular dilatation of the bronchi /
bronchioles (due to inflammation or fibrosis)
 An increase in the caliber of the distal
respiratory tract  no reduction in the
diameter peripherally, visibility in the
subpleural
 Present as tubular or cystic air spaces
depending on the orientation of the bronchi
in the cross-section.

Characteristics:
 Small linear or curved intralobular opacities
measuring <10 mm forming an irregular
reticulation
 Can be isolated or associated with other signs Isolated and subtle subpleural intralobular
reticulations.
3) Intralobular
Reticulations/Lines
= Visible as fine linear opacities in a lobule when the intralobular interstitial tissue is
abnormally thickened. When numerous, may appear as a fine reticular pattern.

B.HRCT –Nodular Pattern
= Focal rounded opacities < 3 mm.
 Based on their anatomic distribution,
nodules can be classified as:
1) Perilymphatic nodules
2) Random nodules
3) Centrilobular nodules

1) Perilymphatic
nodules
= well defined nodules < 3 mm, their distribution
is along the lymphatic vessels: :
 subpleural regions and adjacent to fissures,
 parahilar region adjacent to vessels and
bronchi,
 interlobular septa,
Simulated perilymphatic nodules.
Nodules are visible in:
 subpleural regions (yellow arrows),
 peribronchovascular regions (red arrows),
 interlobular septa (blue arrow).

1) Perilymphatic
nodules
Perilymphatic nodules in patients with sarcoidosis.
 Nodules involve the subpleural interstitium
(large arrows) in the lung periphery and
adjacent to the fissure.
 Parahilar peribronchovascular nodules (small
arrows) also are visible.
Perilymphatic nodules with clear outlines &
high densities distributed along fissures,
peripheral pleura, and intralobular septa.

Smithuis R., et al., HRCT – Basic Interpretation: Radiology Assistant, 2006
1) Perilymphatic
nodules
Differential Diagnoses

2) Random
nodules
Random nodules:
 Nodules with identical diameters spread at regular
intervals across the two pulmonary areas.
 Without any predominance of topographical
elements compared to the pleural surface,
fissures, bronchovascular elements, and
boundaries of the lobule
 The overall distribution appears diffuse and uniform.
Simulated random nodules. Some nodules
involve the pleural surfaces (arrows), but
the overall distribution is uniform.

2) Random
nodules
Chung, J. H.; Walker, C. M., Muller's Imaging of the Chest, 2nd ed.; Elsevier: Philadelphia, 2019.
Random nodules in miliary tuberculosis.
The nodules are small, sharply defined, and diffuse
and uniform in distribution. Some nodules are seen at
the pleural surface.
Sarcoidosis: miliary pattern. HRCT shows diffuse small
nodules resulting in a military pattern.
Subcarinal lymph node enlargement also is noted.
Diff. diagnoses:
• Sarcoidosis
• Miliary infections
• Hematogenous metastases

3) Centrilobular
nodules
 Spare the pleural surfaces (unless they are large)
 Tend to be centered 5 to 10 mm from the pleural surface
or fissures.
 Appear evenly spaced (because lobules are of similar
size)
 Well / ill defined or appear as a rosette of smaller nodules.
Simulated centrilobular nodules.

3) Centrilobular
nodules
Centrilobular nodules in hypersensitivity pneumonitis.
Note that the nodules spare the fissure (arrow) and
pleural surface. The nodules are diffuse and
appear evenly spaced.
Hypersensitivity pneumonitis with
centrilobular nodules of ground-glass
opacity.

Centrilobular Tree-in-Bud
Pattern
 Represents the presence of dilated and fluid-filled (with mucus/pus) centrilobular bronchioles.
 Nodular branching opacities are visible in the lung periphery, larger than normal branching vessels.
 Tend to be centered 5 to 10 mm from the pleural surface when they are seen in the peripheral lung.
 Centrilobular nodules or clusters of nodules (rosettes) also may be seen.

B. HRCT –Nodular Pattern
Algorithms for Classification and Diagnosis of Multiple Small Nodules

C.HRCT –IncreasedAttenuationPattern
May be classified as:
1) Consolidation
2) Ground-glass Opacity
(GGO)

1) Consolidation
 Increase in lung opacity, generally homogenous, associated with:
 Obscuration of the margins of vessels, and airway walls
 Air bronchogram could be present
 Little to no degree of pulmonary collapse
 If another pattern also is present, the consolidation probably represents confluent disease 
should be ignored for the purposes of differential diagnosis.
Homogeneous areas of consolidation in the
peripheral lung in a patient with chronic eosinophilic
pneumonia.
Patchy areas of consolidation with air bronchogram
in Organizing Pneumonia (OP).

Air-Space Consolidation: Differential
Diagnosis

Fine reticular pattern associated with
GGO, some septal thickening is also
visible, in a patient with Pulmonary
Alveolar
Proteinosis (PAP)
2) Ground-glass Opacity
(GGO)
= Slightly increased attenuation of lung parenchyma, with preservation of vascular and
bronchial margins.
Patchy GGO in a patient with
Hypersensitivity Pneumonitis (HP).

GGO Differential
Diagnosis

Crazy Paving
 = combination of GGO and interlobular septal thickening
 Nonspecific, may be seen with a variety of acute lung diseases (e.g. Pneumocystis or
viral pneumonia, edema, hemorrhage, and acute lung injury)
 Among patients with chronic lung disease  it is a classic finding for PAP
 May be seen in any chronic infiltrative lung disease characterized by GGO.
GGO with “crazy paving”. Patchy GGO is
associated with interlobular septal thickening in
the abnormal regions. This represents alveolar
proteinosis.

GGO associated with traction
bronchiectasis
 When they are seen in the same lung regions  the GGO is likely to be due to fibrosis
rather than active disease.
 in most cases, the differential diagnosis is the same as for fibrosis with traction
bronchiectasis.
Fibrosis in the posterior lung bases is associated with GGO and
reticulation. The presence of traction bronchiectasis (arrows) indicates
that the GGO is likely due to fibrosis.

D.HRCT–DecreasedLungAttenuationPattern
 Geographic areas of decreased lung attenuation may represent:
1) Emphysema
2) Cyst
3) Mosaic perfusion
4) Air trapping (on expiratory scans).
 Circumscribed areas of decreased lung attenuation may represent emphysema
or
lung cysts.

1) Emphysema
 Emphysema results in areas of very low attenuation, usually less than −950 HU.
 Typical appearances are as follows:
 Centrilobular emphysema: focal areas of lucency without (or sometimes with) visible
walls, usually with an upper lobe predominance.
 Panlobular emphysema: large areas of low attenuation, usually diffuse and associated with
decreased vessel size.
 Paraseptal emphysema: subpleural lucencies marginated by interlobular septa,
or subpleural bullae, usually with an upper lobe predominance.

2) Cyst
 A nonspecific term, used to describe a thin-walled (usually <3 mm), well-defined,
circumscribed, air-containing lesion, ≥1 cm in diameter.
 The adjacent pulmonary parenchyma can be strictly normal or present
associated lesions: nodules, GGO, septal thickening, or reticular pattern.
Multiple cysts throughout the lung parenchyma in a young
female patient. Note that the adjacent lung is unremarkable.
Patient with Sjögren’s syndrome and lymphoid interstitial
pneumonia. There’s bilateral GGO and multiple thin-walled
cysts.

2)
Cyst
Ferretti, G.; Imaging Atlas of Interstitial Lung Disease. Boehringer Ingelheim International: 2019.

3) Mosaic Attenuation
= Coexistence of high-density parenchymal areas and normal/low-density areas of
the lungs.
 can translate into three types of anomalies:
• obstructive small airways disease
• alveolar interstitial infiltration
• occlusive disease of the small pulmonary arteries
Respiratory bronchiolitis–interstitial
lung disease: HRCT scan at
inspiration shows mosaic attenuation.

Diffuse constrictive bronchiolitis in a bone marrow
transplant patient.
Patchy heterogeneous mosaic attenuation alternating
between normal dense areas and hypodense areas
suggesting expiratory air trapping, revealing small
airways disease.
Ferretti, G.; Imaging Atlas of Interstitial Lung Disease. Boehringer Ingelheim International: 2019.
3) Mosaic
Attenuation
Head cheese sign of pulmonary mosaic attenuation

• 4) Air Trapping
• = Retention of air in the lung distal to an obstruction (usually partial).
•  seen on end expiration scans as parenchymal areas with less than normal
• increase in attenuation and lack of volume reduction.
 Mosaic perfusion and air trapping look the same, often are related, but they
are
• distinct findings.
 Mosaic perfusion: inspiratory scan finding,
 Air trapping: expiratory scan finding.
 In some patients with airway disease, air trapping may be visible on
expiratory scans even though inspiratory scans are normal.

Air trapping in chronic hypersensitivity pneumonitis. (A) HRCT shows diffuse
GGO, minimal fibrosis, and focal areas of decreased attenuation and
vascularity (mosaic attenuation). (B) Expiratory CT accentuates the areas of
air-trapping.
4) Air
Trapping

HRCT–DistributionofPattern

Raghu. Am J Respir Crit Care Med. 2018;198:e44.
UIP Probable UIP Indeterminate for UIP Alternative Diagnosis
• Subpleural/basal
predominant
• HRCT with
honeycombing +/-
peripheral traction
bronchiectasis or
bronchiolectasis
predominant
• Reticular pattern with
peripheral traction
bronchiectasis or
bronchiolectasis
• May have ground-
glass opacities (GGO)
predominant
• Subtle reticulation
• No specific etiology
suggested from CT
• CT with cysts, marked
mosaic attenuation,
predominant GGO,
profuse
micronodules,
centrilobular nodules,
nodules, or
consolidation
• Peribronchovascular,
perilymphatic, or
upper- or mid-lung
distribution
70
HRCT Patterns (ATS 2018)

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