Thoracic imaging terms part 1

Thoracic Imaging Terms

By

Gamal Rabie Agmy , MD , FCCP Professor of Chest Diseases ,Assiut University

ERS National Delegate of Egypt

Air Bronchogram

An air bronchogram is a pattern of air-filled

(low-attenuation) bronchi on a background

of opaque (high-attenuation) airless lung . The

sign implies

(a) patency of proximal airways and

(b) evacuation of alveolar air by means of

absorption (atelectasis) or replacement

(eg, pneumonia) or a combination of these

processes.

(c) In rare cases, the displacement of air is

the result of marked interstitial expansion

(eg, lymphoma) .

Air Crescent

An air crescent is a collection of air in a

crescentic shape that separates the wall of

a cavity from an inner mass .The air

crescent sign is often considered

characteristic of either Aspergillus colonization of preexisting cavities or

retraction of infarcted lung in angioinvasive

aspergillosis .However, the air crescent

sign has also been reported in other

conditions, including tuberculosis,

Wegener granulomatosis, intracavitary

hemorrhage, and lung cancer.

Air Trapping

Air trapping is retention of air in the lung

distal to an obstruction (usually partial). Air

trapping is seen on end-expiration CT

scans as parenchymal areas with less

than normal increase in attenuation and

lack of volume reduction. Comparison

between inspiratory and expiratory CT

scans can be helpful when air trapping is

subtle or diffuse. Differentiation from areas

of decreased attenuation resulting from

hypoperfusion as a consequence of an

occlusive vascular disorder (eg, chronic

thromboembolism) may be problematic ,

but other findings of airways versus

vascular disease are usually present.

Where is the pathology ???????

in the areas with increased density meaning there is ground glass

in the areas with decreased density meaning there is air trapping

Pathology in black areas

Airtrapping: Airway Disease

Bronchiolitis obliterans (constrictive bronchiolitis) idiopathic, connective tissue diseases, drug reaction,

after transplantation, after infection

Hypersensitivity pneumonitis granulomatous inflammation of bronchiolar wall

Sarcoidosis granulomatous inflammation of bronchiolar wall

Asthma / Bronchiectasis / Airway diseases

Airway Disease

what you see……

In inspiration sharply demarcated areas of seemingly increased

density (normal) and decreased density

demarcation by interlobular septa

In expiration ‘black’ areas remain in volume and density

‘white’ areas decrease in volume and increase in

density

INCREASE IN CONTRAST

DIFFERENCES

AIRTRAPPING

Bronchiolitis

obliterans

Aortopulmonary Window

Focal concavity in the left mediastinal

border below the aorta and above the left

pulmonary artery can be seen on a frontal

radiograph . Its appearance may be

modified by tortuosity of the aorta. The

aortopulmonary window is a common site

of lymphadenopathy in a variety of

inflammatory and neoplastic diseases.

Lymph nodes

Enlarged hilar shadow with lobulated outlines

Normal

Lymph nodes Anatomic Considerations

Retrosternal Prevascular Retrocaval Aortic window Carinal Subcarinal Hilar Z-esophageal Circm-cardiac

3 3

Lymph nodes

Anatomic Considerations


6 5

Lymph nodes

Anatomic Considerations


7

7

8

9

http://radiographics.rsnajnls.org/cgi/content/full/20/2/449/F4

Apical Cap

The usual appearance is of homogeneous

soft-tissue attenuation capping the extreme lung

apex (uni- or bilaterally), with a sharp or irregular

lower border .Thickness is variable, ranging up to

about 30 mm . An apical cap occasionally mimics

apical consolidation on transverse CT scans.

Architectural Distortion

Lung anatomy has a distorted appearance

and is usually associated with pulmonary

fibrosis and accompanied by volume loss.

Reduced volume is seen, accompanied by

increased opacity (chest radiograph) or

attenuation (CT scan) in the affected

part of the lung . Atelectasis is often

associated with abnormal displacement of

fissures, bronchi, vessels,diaphragm,

heart, or mediastinum .The distribution can

be lobar, segmental, or subsegmental.

Atelectasis is often qualified by descriptors

such as linear,discoid, or platelike.

Atelectasis

The definition of atelectasis is loss of air in the alveoli;

alveoli devoid of air (not replaced).

A diagnosis of atelectasis requires the following:

1-A density, representing lung devoid of air

2-Signs indicating loss of lung volume

Atelectasis

1-Absorption Atelectasis When airways are obstructed there is no further

ventilation to the lungs and beyond. In the early

stages, blood flow continues and gradually the

oxygen and nitrogen get absorbed, resulting in

atelectasis.

Types of Atelectasis:

2-Relaxation Atelectasis The lung is held close to the chest wall because of the

negative pressure in the pleural space. Once the

negative pressure is lost the lung tends to recoil due

to elastic properties and becomes atelectatic. This

occurs in patients with pneumothorax and pleural

effusion. In this instance, the loss of negative

pressure in the pleura permits the lung to relax, due

to elastic recoil. There is common misconception that

atelectasis is due to compression.


3-Adhesive Atelectasis :

Surfactant reduces surface tension and keeps the

alveoli open. In conditions where there is loss of

surfactant, the alveoli collapse and become

atelectatic. In ARDS this occurs diffusely to both

lungs. In pulmonary embolism due to loss of blood

flow and lack of CO2, the integrity of surfactant

gets impaired.



4-Cicatricial Atelectasis

– Alveoli gets trapped in scar and

becomes atelectatic in fibrotic

disorders

.

5-Round Atelectasis An instance where the lung gets trapped by

pleural disease and is devoid of air.

Classically encountered in asbestosis.


.

6-Compression Atelectasis


Generalized 1-Shift of mediastinum: The trachea and heart gets shifted

towards the atelectatic lung.

2-Elevation of diaphragm: The diaphragm moves up and

the normal relationship between left and right side gets

altered.

3-Drooping of shoulder.

4-Crowding of ribs: The interspace between the ribs is

narrower compared to the opposite side.

Signs of Loss of Lung Volume:

Movement of Fissures You need a lateral view to appreciate the movement of

oblique fissures. Forward movement of oblique fissure in

LUL atelectasis. Backward movement in lower lobe

atelectasis.

Movement of transverse fissure can be recognized in the

PA film.


Movement of Hilum The right hilum is normally slightly lower than the left.

This relationship will change with lobar atelectasis.


Compensatory Hyperinflation

Compensatory hyperinflation as evidenced by increased

radiolucency and splaying of vessels can be seen with the

normal lobe or opposite lung.


Alterations in Proportion of Left and

Right Lung

The right lung is approximately 55% and left lung 45%. In

atelectasis this apportionment will change and can be a

clue to recognition of atelectasis. .


Hemithorax Asymmetry In normals, the right and left hemithorax are equal in size.

The size of the hemithorax will be asymmetrical and

smaller on the side of atelectasis


Signs of Loss of Lung Volume: Generalized

Shift of mediastinum: The trachea and heart gets shifted towards the atelectatic lung.

Elevation of diaphragm: The diaphragm moves up and the normal relationship between left

and right side gets altered.

Drooping of shoulder.

Crowding of ribs: The interspace between the ribs is narrower compared to the opposite side.

Movement of Fissures

You need a lateral view to appreciate the movement of oblique fissures. Forward movement of

oblique fissure in LUL atelectasis. Backward movement in lower lobe atelectasis.

Movement of transverse fissure can be recognized in the PA film.

Movement of Hilum

The right hilum is normally slightly lower than the left. This relationship will change with lobar

atelectasis.

Compensatory Hyperinflation

Compensatory hyperinflation as evidenced by increased radiolucency and splaying of vessels

can be seen with the normal lobe or opposite lung.

Alterations in Proportion of Left and Right Lung

The right lung is approximately 55% and left lung 45%. In atelectasis this apportionment will

change and can be a clue to recognition of atelectasis.

Hemithorax Asymmetry

In normals, the right and left hemithorax are equal in size. The size of the hemithorax will be

asymmetrical and smaller on the side of atelectasis

Atelectasis Right Lung Homogenous density right hemithorax

Mediastinal shift to right

Right hemithorax smaller

Right heart and diaphragmatic silhouette are not identifiable

Atelectasis Left Lung

Homogenous density left hemithorax

Mediastinal shift to left

Left hemithorax smaller

Diaphragm and heart silhouette are not identifiable

Atelectasis Left Lung •Homogenous density left hemithorax

•Mediastinal shift to the left

•Left hemithorax smaller •Diaphragmatic and heart silhouette are not identifiable

Left Lower Lobe Atelectasis • Inhomogeneous cardiac density

• Left hilum pulled down

• Non-visualization of left diaphragm

• Triangular retrocardiac atelectatic LLL

Atelectasis Left Lower Lobe Double density over heart

Inhomogenous cardiac density

Triangular retrocardiac density

Left hilum pulled down

Other findings include:

Pneumomediastinum

Atelectasis Left

Upper Lobe

Mediastinal shift to left

Density left upper lung field

Loss of aortic knob and left hilar

silhouettes

Herniation of right lung

Atelectatic left upper lobe

Forward movement of left

oblique fissure "Bowing sign"

Atelectasis Left Upper

Lobe

Hazy density over left

upper lung field

Loss of left heart

silhouette

Tracheal shift to left

Lateral A: Forward movement of

oblique fissure

B: Herniated right lung

C: Atelectatic LUL

Lateral Movement of oblique and transverse

fissures

Atelectasis Right Upper Lobe

Homogenous density right upper lung

field


Loss of silhouette of ascending aorta

Lateral Movement of oblique and transverse

fissures

Atelectasis Right Upper Lobe

Homogenous density right upper lung field


Loss of silhouette of ascending aorta

RML Atelectasis

Vague density in right lower lung field, almost normal

RML atelectasis in lateral view, not evident in PA view

Vague density in right lower lung field (almost a normal film).

Dramatic RML atelectasis in lateral view, not evident in PA view. Movement of

transverse fissure.

Other findings include: Azygous lobe

Atelectasis Right Lower Lobe Density in right lower lung field

Indistinct right diaphragm

Right heart silhouette retained

Transverse fissure moved down

Right hilum moved down

Adhesive Atelectasis

Alveoli are kept open by the integrity of surfactant. When there is loss

of surfactant, alveoli collapse. ARDS is an example of diffuse alveolar

atelectasis.

Plate-like atelectasis is an example of focal loss of surfactant.

Relaxation Atelectasis

The lung is held in apposition to the chest wall because of negative pressure

in the pleura. When the negative pressure is lost, as in pneumothorax or

pleural effusion, the lung relaxes to its atelectatic position. The atelectasis is

a secondary event. The pleural problem is primary and dictates other

radiological findings.

Round Atelectasis

Mass like density

Pleural based

Base of lungs

Blunting of costophrenic angle

Pleural thickening

Pulmonary vasculature curving

into the density

Esophageal surgical clips

Round Atelectasis

Mass like density

Pleural based

Base of lungs

Blunting of costophrenic angle, pleural thickening

Pulmonary vasculature curving into the density

RML Lateral Segment Atelectasis

Sub-segmental Atelectasis

Atelectasis

Segmental

Anterior sub-segment of RUL

"Bronchial wedge"

The azygoesophageal recess on a frontal

chest radiograph, is seen as a vertically

oriented interface between the right lower

lobe and the adjacent mediastinum (the

medial limit of the recess). Superiorly, the

interface is seen as a smooth arc with

convexity to the left. Disappearance or

distortion of part of the interface suggests

disease (eg, subcarinal lymphadenopathy).

On CT scans, the recess merits

attentionbecause small lesions located in

the recess will often be invisible on chest

radiographs

Azygoesophageal Recess

Acute interstitial pneumonia, or AIP

In the acute phase, patchy bilateral

groundglass opacities are seen , often with

some sparing of individual lobules,

producing a geographic appearance;

dense opacification is seen in the

dependent lung .

In the organizing phase, architectural

distortion, traction bronchiectasis, cysts,

and reticular opacities are seen .

Azygos Fissure

Beaded Septum Sign

This sign consists of irregular and nodular

thickening of interlobular septa reminiscent

of a row of beads . It is frequently seen in

lymphangitic spread of cancer and less

often in sarcoidosis .

Bleb

Anatomy.—A bleb is a small gas-containing space

within the visceral pleura or in the subpleural lung,

not larger than 1 cm in diameter . CT scans.—A

bleb appears as a thin-walled cystic air space

contiguous with the pleura. Because the arbitrary

(size) distinction between a bleb andbulla is of little

clinical importance, the use of this term by

radiologists is discouraged.

Bulla

<1m m wa ll

>1cm size

Pneum atocele

<1m m wa ll

staph . in fection

Honey com bing

<1cm size

m u ltip le equal

Cyst

1-3m m wa ll

1 -10 cm size

Cavity

>3m m wa ll

A ny size

C avitary lesions o f lung

Bulla

Definition

•Thin-walled–less than 1 mm

•Air-filled space

•In the lung> 1 cm in size and up to 75% of lung

•Walls may be formed by pleura, septa,

or compressed lung tissue.

•Results from destruction, dilatation and

confluence of airspaces distal to terminal

bronchioles.

•Bullous disease may be primary or associated

with emphysema or interstitial lung disease.

• Primary bullous lung disease may be familial

and has been associated with Marfan's, Ehler's

Danlos, IV drug users, HIV infection, and

vanishing lung syndrome.

•Bullae may occasionally become very large

and compromise respiratory function. Thus

has been referred as vanishing lung syndrome,

and may be seen in young men.

Upper lobe Bulla

Lower lobe Bulla

A: Xray shows bilateral bulla.

B: CT shows bilateral bulla.

C: CT after bullectomy.

Pneumatocele is a benign air containing cyst of lung, with

thin wall < 1mm as bulla but with different mechanism

Infection with staph aureus is the commonest cause ( less

common causes are, trauma, barotrauma) lead to necrosis

and liquefaction followed by air leak and subpleural

dissection forming a thin walled cyst.

•Honeycombing is defined as multiple cysts < 1cm in diameter,with

well defined walls, in a background of fibrosis, tend to form

clusters and is considered as end stage lung .

•It is formed by extensive interstitial fibrosis of lung with residual

cystic areas.

A cyst is a ring

shadow > 1 cm in

diameter and up to

10 cm with wall

thickness from 1-3

mm.

Thin walled cysts of LAM

A cavity is > 1cm

in diameter, and its

wall thickness is

more than 3 mm.

•A central portion necrosis and communicate to bronchus.

•The draining bronchus is visible (arrow). CT (2 mm slice thickness)

shows discrete air bronchograms in the consolidated area.

Mechanism

1. Site

A cavity in apicoposterior segment of left upper lobe

2.Number

Multiple cavities:

1. Aspiration.

2. TB

3. Fungal.

4. Metastatic.

5. Septic emboli.

6.Wegners granulomatosis

Multiple cysts of metastasis

from squamous cell

carcinoma.

Multiple thick wall cavities from

adenocarcinoma of right lung

Irregular , nodular inner lining of thick wall abscess

Malignant cavity.

3. Thickness and

irregularity

4. eccentric

Malignant

5. Relation to lymph

node enlargement

6. Contents

•Arrow head Crescent sign.

•Black arrows Fibrotic bands surrounding cavity

(Fibrocavitary TB).

Morphologic criteria on thin-section CT

scans include bronchial dilatation with

respect to the accompanying pulmonary

artery (signet ring sign), lack of tapering

of bronchi, and identification of bronchi

within 1 cm of the pleural surface (27)

(Fig 11). Bronchiectasis may be classified

as cylindric, varicose, or cystic, depending

on the appearance of the affected bronchi.

It is often accompanied by bronchial wall

thickening, mucoid impaction, and small-

airways abnormalities

Bronchiectasis

Bronchiolectasis

When dilated bronchioles are filled with

exudate and are thick walled, they are

visible as a tree-in-bud pattern or as

centrilobular nodules. In traction

bronchiolectasis, the dilated bronchioles

are seen as small, cystic, tubular

airspaces, associated with CT findings of

fibrosis

bronchocele is a tubular or branching Yor

V-shaped structure that may resemble a

gloved finger (Fig 13). The CT attenuation

of the mucus is generally that of soft tissue

but may be modified by its composition

(eg, high-attenuation material in allergic

bronchopulmonary aspergillosis). In the

case of bronchial atresia, the surrounding

lung may be of decreased attenuation

because of reduced ventilation and, thus,

perfusion.

Bronchocele

Bronchiolitis

This direct sign of bronchiolar inflammation

(eg, infectious cause) is most often seen

as the tree-inbud pattern, centrilobular

nodules, and bronchiolar wall thickening .

This descriptor is applied to disease that is

conspicuously centered on macroscopic

bronchovascular bundles . Examples of

diseases with a bronchocentric distribution

include sarcoidosis , Kaposi sarcoma , and

organizing pneumonia

Bronchocentric

The imaging appearance is of a small

calcific focus in or immediately adjacent to

anairway (Fig 15), most frequently the right

middle lobe bronchus. Broncholiths are

readily identified on CT scans . Distal

obstructive changes may include

atelectasis, mucoid impaction, and

bronchiectasis.

Broncholith

An airspace measuring more than 1 cm—

usually several centimeters in diameter,

sharply demarcated by a thin wall that is no

greater than 1 mm in thickness. A bulla is

usually accompanied by emphysematous

changes in the adjacent lung.

Radiographs and CT scans.—

A bulla appears as a rounded focal lucency

or area of decreased attenuation, 1 cm or

more in diameter, bounded by a thin wall .

Multiple bullae are often present and are

associated with other signs of pulmonary

emphysema (centrilobular and paraseptal).

Bulla

A cavity is a gas-filled space, seen as a

lucency or low-attenuation area, within

pulmonary consolidation, a mass, or a

nodule . In the case of cavitating

consolidation, the original consolidation

may resolve and leave only a thin wall. A

cavity is usually produced by the expulsion

or drainage of a necrotic part of the lesion

via the bronchial tree. It sometimes

contains a fluid level. Cavity is not a

synonym for abscess.

Cavity

Cavitary Lung Lesions

Number:

Multiple bilateral cavities would raise

suspicion for either bronchiogenous or

hematogenous process. You should consider:

Aspiration lung abscess

Septic emboli

Metastatic lesions

Vasculitis (Wegener's)

Coccidioidomycosis, tuberculosis

Location:

• Classical locations for aspiration lung abscess are superior segment of the lower lobes posterior segments of upper lobes.

• Tuberculous cavities are common in superior segments of upper and lower lobes or posterior segments of upper lobes.

• When a cavity in anterior segment is encountered, a strong suspicion for lung cancer should be raised. TB and aspiration lung abscess are rare in anterior segments. Cancer lung can occur in any segment.

Wall Thickness:

• Thick walls are seen in:

– Lung abscess

– Necrotizing squamous cell lung cancer

– Wegener's granulomatosis

– Blastomycosis

Wall Thickness:

• Thin walled cavities are seen in:

• Coccidioidomycosis

• Metastatic cavitating squamous cell carcinoma from the cervix

• M. Kansasii infection

• Congenital or acquired bullae

• Post-traumatic cysts

• Open negative TB

Contents:

• The most common cause for air fluid level is lung abscess. Air fluid levels can rarely be seen in malignancy and in tuberculous cavities from rupture of Rasmussen's aneurysm.

• A fungous ball should make you consider aspergillosis. A blood clot and fibrin ball will have the same appearance.

• Floating Water Lily: The collapsed membrane of a ruptured echinococcal cyst, floats giving this appearance.

Lining of Wall:

The wall lining is irregular and nodular in

lung cancer or shaggy in lung abscess

Evolution of Lesion:

Many times review of old films to assess the

evolution of the radiological appearance of

the lesion extremely helpful. Examples

• Infected bullae

• Aspergilloma

• Sub acute necrotizing aspergillosis

• Bleeding from Rasmussen's aneurysm in a

tuberculous cavity

Associated Features:

Ipsilateral lymph nodes or lytic

lesions of the bone is seen

with malignancy

Centrilobular

A small dotlike or linear opacity in the center of a normal secondary

pulmonary lobule, most obvious within 1 cm of a pleural surface,

represents the intralobular artery (approximately1 mm in diameter) .

Centrilobular abnormalities include

(a) nodules,

(b) a tree-in-bud pattern indicating small-airways disease,

(c) increased vis-ibility of centrilobular structures due to thickening

or infiltration of the adjacent interstitium, or

(d) abnormal areas of low attenuation caused by centrilobular

emphysema

CT findings are centrilobular areas of

decreased attenuation, usually without visible

walls, of nonuniform distribution and

predominantly located in upper lung zones .

The term centriacinar emphysema is

synonymous.

Centrilobular Emphysema

Consolidation appears as a homogeneous

increase in pulmonary parenchymal

attenuation that obscures the margins of

vessels and airway walls .An air

bronchogram may be present. The

attenuation characteristics of consolidated

lung are only rarely helpful in differential

diagnosis (eg, decreased attenuation in

lipoid pneumonia and increased in

amiodarone toxicity

Consolidation

Crazy-paving Pattern

This pattern appears as thickened

interlobular septa and intralobular lines

superimposed on a background of ground-

glass opacity , resembling irregularly

shaped paving stones. The crazy-paving

pattern is often sharply demarcated from

more normal lung and may have a

geographic outline. It was originally

reported in patients with alveolar

proteinosis and is also encountered in

other diffuse lung diseases that affect both

the interstitial and airspace compartments,

such as lipoid pneumonia

Cyst A cyst appears as a round parenchymal

lucency or low-attenuating area with a

well-defined interface with normal lung.

Cysts have variable wall thickness but

are usually thin-walled (2 mm) and

occur without associated pulmonary

emphysema . Cysts in the lung

usually contain air but occasionally contain

fluid or solid material. The term is

often used to describe enlarged thinwalled

airspaces in patients with

lymphangioleiomyomatosis or Langerhans

cell histiocytosis ; thickerwalled

honeycomb cysts are seen in patients with

end-stage fibrosis .

Ground-glass opacity is the dominant

abnormality and tends to have a basal and

peripheral distribution . Microcystic or

honeycomb changes in the area of ground-

glass opacity are seen in some cases .

Desquamative Interstitial Pneumonia

or DIP

Ground-Glass Opacity or GGO

it appears as hazy increased opacity of

lung, with preservation of bronchial and

vascular margins .It is caused by partial

filling of airspaces, interstitial thickening

(due to fluid, cells, and/or fibrosis), partial

collapse of alveoli, increased capillary

blood volume, or a combination of these,

the common factor being the partial

displacement of air .Ground-glass opacity

is less opaque than consolidation, in which

bronchovascular margins are obscured.

T h e h a l o s i g n i s a C T f i n d i n g

of ground-glass opacity surrounding a

n o d u l e o r m a s s . I t w a s f i r s t

descr i bed as a si gn of hemor rhage

around foci of invasive aspergi l losis

. The ha lo s i gn i s non spec i f i c and

may also be caused by hemorrhage

associated with other types of nodules

o r b y l o c a l p u l mo n a r y i n f i l t r a t i o n

by neoplasm (eg , adenocarcinoma) .

Halo Sign

On chest radiographs, honeycombing appears as

closely approximated ring shadows, typically 3–10

mm in diameter with walls 1–3 mm in thickness, that

resemble a honeycomb; the finding implies end-

stage lung disease. On CT scans, the appearance is

of clustered cystic air spaces, typically of

comparable diameters on the order of 3–10 mm but

occasionally as large as 2.5 cm . Honeycombing is

usually subpleural and is characterized by well-

defined walls . It is a CT feature of established

pulmonary fibrosis . Because honeycombing is often

considered specific for pulmonary fibrosis and is an

important criterion in the diagnosis of usual

interstitial pneumonia (63), the term should be used

with care, as it may directly impact patient care.

Honeycombing

The typical imaging findings are reticular

opacities and honeycombing, with a

predominantly peripheral and basal

distribution . Ground-glass opacity, if

present, is less extensive than reticular and

honeycombing patterns. The typical

radiologic findings are also encountered in

usual interstitial pneumonia secondary to

specific causes, such as asbestos-induced

pulmonary fibrosis (asbestosis), and the

diagnosis is usually one of exclusion.

Idiopathic pulmonary fibrosis

A pulmonary infarct is typically triangular or

dome-shaped, with the base abutting the

pleura and the apex directed toward the

hilum.The opacity represents local

hemorrhage with or without central tissue

necrosis

Infarction

Interlobular septal thickening

This finding is seen on chest radiographs as thin linear

opacities at right angles to and in contact with the lateral

pleural surfaces near the lung bases (Kerley B lines); it is

seen most frequently in lymphangitic spread of cancer or

pulmonary edema. Kerley A lines are predominantly

situated in the upper lobes, are 2–6 cm long, and can be

seen as fine lines radially oriented toward the hila. In recent

years, the anatomically descriptive terms septal lines and

septal thickening have gained favor over Kerley lines. On

CT scans, disease affecting one of the components of the

septa (see interlobular septum) may be responsible for

thickening and so render septa visible. On thin-section CT

scans, septal thickening may be smooth or nodular , which

may help refine the differential diagnosis.

Interlobular septum

Interlobular septa appear as thin linear

opacities between lobules ; these septa are

to be distinguished from centrilobular

structures. They are not usually seen in the

healthy lung (normal septa are

approximately 0.1 mm thick) but are clearly

visible when thickened (eg, by pulmonary

edema).

Interstitial emphysema is rarely recognized

radiographically in adults and is

infrequently seen on CT scans . It appears

as perivascular lucent or lowattenuating

halos and small cysts

Interstitial emphysema

Intralobular lines are visible as fine linear

opacities in a lobule when the intralobular

interstitial tissue is abnormally thickened .

When numerous, they may appear as a

fine reticular pattern. Intralobular lines may

be seen in various conditions, including

interstitial fibrosis and alveolar proteinosis

Intralobular lines

Health & Medicine

Thoracic imaging terms part 1