3. The interstitium of the lung is not normally visible radiographic-
ally; it becomes visible only when disease (e.g., edema, fibrosis,
tumor) increases its volume and attenuation.
The interstitial space is defined as continuum of loose
connective tissue throughout the lung composed of three
subdivisions:
(i) the bronchovascular (axial), surrounding the bronchi,
arteries, and veins from the lung root to the level of the
respiratory bronchiole
(ii) the parenchymal (acinar), situated between the alveolar and
capillary basement membranes
(iii) the subpleural, situated beneath the pleura, as well as in the
interlobular septae.
The Lung Interstitium
4.
5. Secondary lobule
For the purposes of the interpretation of HRCT, the
secondary lobule is most appropriately conceptualized
as having three principal parts or components:
Interlobular septa and contiguous subpleural
interstitium
Centrilobular structures
Lobular parenchyma and acini
14. Patterns of Interstitial Lung Disease
Generally, HRCT findings of lung disease can be
classified into four large categories based on their
appearances. These are
(i) linear and reticular opacities,
(ii) nodules and nodular opacities,
(iii) increased lung opacity, and
(iv) abnormalities associated with decreased lung
opacity, including cystic lesions, emphysema, and
airway abnormalities.
15. Linear and reticular opacities,
Thickening of the interstitial fiber
network of the lung by fluid or fibrous
tissue, or because of interstitial
infiltration by cells or other material,
primarily results in an increase in linear
or reticular lung opacities as seen on
HRCT
16. Linear and reticular opacities,
Linear or reticular opacities may be manifested by the
interface sign,
peribronchovascular interstitial thickening,
interlobular septal thickening,
parenchymal bands,
subpleural interstitial thickening,
intralobular interstitial thickening,
honeycombing,
irregular linear opacities, &
subpleural lines
17.
18. Interface sign
The presence of irregular interfaces between the
aerated lung parenchyma and bronchi, vessels, or
visceral pleural surfaces has been termed the interface
sign. The interface sign is nonspecific, and is
commonly seen in patients with an interstitial
abnormality, regardless of its cause. In the original
description of the interface sign, this finding was
visible in 89% of patients with interstitial lung disease
19.
20. Peribronchovascular Interstitial
Thickening
Central bronchi and pulmonary arteries are
surrounded and enveloped by a strong connective
tissue sheath, termed the peribronchovascular
interstitium, extending from the level of the
pulmonary hila into the peripheral lung. In the lung
periphery, the peribronchovascular interstitium
surrounds centrilobular arteries and bronchioles, and,
more distally, supports the alveolar ducts and alveoli
The peribronchovascular interstitium is also termed
the axial interstitium by Weibel.
27. Interlobular Septal Thickening
Thickened septa 1 to 2 cm in length may outline part
of or an entire lobule and are usually seen extending to
the pleural surface, being roughly perpendicular to the
pleura
Lobules at the pleural surface may have a variety of
appearances, but they are often longer than they are
wide, resembling a cone or truncated cone.
Within the central lung, thickened septa outline
lobules that are 1 to 2.5 cm in diameter and appear
polygonal, or sometimes hexagonal, in shape
38. Subpleural Interstitial
Thickening
Thickening of the interlobular septa within the
peripheral lung is associated with thickening of the
subpleural interstitium
differential diagnosis of subpleural interstitial
thickening is the same as that of interlobular septal
thickening, although subpleural interstitial thickening
is more common than septal thickening in patients
with IPF or UIP of any cause
39. Parenchymal Bands
The term parenchymal band has been used to describe
a nontapering, reticular opacity, usually several
millimeters in thickness and from 2 to 5 cm in length,
seen in patients with atelectasis, pulmonary fibrosis,
or other causes of interstitial thickening
40.
41.
42. Honeycombing
Honeycombing is defined by the presence of small air-
containing cystic spaces, generally lined by
bronchiolar epithelium and having thickened walls
composed of dense fibrous tissue. Honeycombing
indicates the presence of end-stage lung and can be
seen in many diseases leading to end-stage pulmonary
fibrosis
45. This 50-year-old man presented with end-stage lung fibrosis
PA chest radiograph shows medium to coarse reticular
B: CT scan shows multiple small cysts (honeycombing) involving
predominantly the subpleural peripheral regions of lung. Traction
bronchiectasis, another sign of end-stage lung fibrosis.
46. Subpleural Lines
curvilinear opacity a few millimeters or less in
thickness, less than 1 cm from the pleural surface and
paralleling the pleura, is termed a subpleural line .
It is a nonspecific indicator of atelectasis, fibrosis, or
inflammation. It was first described in patients with
asbestosis , it was termed a subpleural curvilinear
shadow.
47.
48. Nodular pattern
The term nodule is defined as a rounded opacity, at
least moderately well-defined, and no more than 3 cm
in diameter
The term small nodule is used to define a rounded
opacity smaller than 1 cm in diameter,
whereas large nodule is used to refer to nodules 1 cm or
larger in diameter.
Some authors have used micronodule to describe
nodules smaller than 7 mm in diameter.
51. 3.Random Distribution
Small nodules that appear randomly distributed in
relation to structures of the secondary lobule and lung
are often seen in patients with miliary tuberculosis
miliary fungal infections, and hematogenous
metastases
53. 2.Centrilobular Distribution
Centrilobular nodules can reflect the presence of
either interstitial or airspace abnormalities, and the
histologic correlations reported to occur in association
with centrilobular nodules vary with the disease entity
Centrilobular nodules may be dense and of
homogeneous opacity, or of ground-glass opacity and
may range from a few millimeters to a centimeter in
size.
67. Hematogenous metastases and nodular ILD. This 45-year-old
woman presented with metastatic gastric carcinoma. The PA
chest radiograph shows a diffuse pattern of nodules, 6 to 10
mm in diameter.
69. Reticulonodular pattern
A reticulonodular pattern results from a combination
of reticular and nodular opacities.
This pattern is often difficult to distinguish from a
purely reticular or nodular pattern, and in such a case a
differential diagnosis should be developed based on
the predominant pattern.
If there is no predominant pattern, causes of both
nodular and reticular patterns should be considered.
most commonly in silicosis,sarcoidosis.
72. Decreased Lung Opacity
A variety of abnormalities result in decreased lung
attenuation or air-filled cystic lesions on HRCT. These
include
honeycombing,
lung cysts,
emphysema, bullae,
pneumatoceles,
cavitary nodules,
bronchiectasis,
mosaic perfusion,
air-trapping due to airways disease
73.
74. Honeycombing/cyst
Honeycombing is defined by the presence of small air-
containing cystic spaces, generally lined by
bronchiolar epithelium and having thickened walls
composed of dense fibrous tissue. Honeycombing
indicates the presence of end-stage lung and can be
seen in many diseases leading to end-stage pulmonary
fibrosis
79. Bullae
Emphysematous bullae are well seen using HRCT. A
bulla has been defined as a
sharply demarcated area of emphysema measuring 1
cm or more in diameter and possessing a thin
epithelialized wall that is usually no thicker than 1 mm
80. Blebs
The term bleb is used pathologically to refer to a gas-
containing space within the visceral pleura
Radiographically, this term is sometimes used to
describe a focal thin-walled lucency contiguous with
the pleura, usually at the lung apex.
However, the distinction between bleb and bulla is of
little practical significance and is seldom justified. The
term bulla is preferred
89. Pulmonary edema
sparing of the apices and extreme lung bases
characteristic ‘butterfly’ or ‘bat's wing’ distribution
90. Pulmonary edema
There is diffuse ground-glass opacification,
smooth thickening of multiple interlobular
septa and peribronchovascular cuffing.
Bilateral pleural effusions are also seen.
94. Systemic sclerosis.
A: PA chest radiograph shows a bibasilar and subpleural distribution of fine
reticular ILD. The presence of a dilated esophagus (arrows) provides a clue to
the correct diagnosis.
B: CT scan shows peripheral ILD and a dilated esophagus (arrow).
95. A middle or upper lung predominant distribution
suggests: (Mycobacterium Settle Superiorly in
Lung)
1. Mycobacterial or fungal disease
2. Silicosis
3. Sarcoidosis
4. Langerhans Cell Histiocytosis
Rule no. 3
96. Complicated silicosis. PA chest radiograph shows multiple nodules
involving the upper and middle lungs, with coalescence of nodules
in the left upper lobe resulting in early progressive massive fibrosis
97. Sarcoidosis. CT scan shows nodular thickening of the bronchovascular bundles
(solid arrow) and subpleural nodules (dashed arrow), illustrating the typical
perilymphatic distribution of sarcoidosis.
98. Langerhan cell histiocytosis.
This 50-year-old man had a
30 pack-year history of
cigarette smoking.
A: PA chest radiograph shows
hyperinflation of the lungs
and fine bilateral reticular
ILD.
B: CT scan shows multiple
cysts (solid arrow) and
nodules (dashed arrow).
103. Cardiogenic pulmonary edema.
PA chest radiograph shows enlargement of the cardiac
silhouette, bilateral ILD, enlargement of the azygos vein (solid
arrow), and peribronchial cuffing (dashed arrow).
104. Lymphangitic carcinomatosis. This 53-year-old man presented
with chronic obstructive pulmonary disease and large-cell
bronchogenic carcinoma of the right lung.
CT scan shows unilateral nodular thickening (arrows) and a
malignant right pleural effusion.
106. Lymphangioleiomyomatosis
(LAM).
A: PA chest radiograph shows a
right basilar pneumothorax and
two right pleural drainage
catheters. The lung volumes are
increased, which is characteristic
of LAM, and there is diffuse
reticular ILD.
B: CT scan shows bilateral thin-
walled cysts and a loculated right
pneumothorax (P).