1) HRCT shows reticular pattern involving subpleural areas of the superior segment of lower lobes with some interlobular septal thickening, suggestive of usual interstitial pneumonia. 2) There is also a reticular pattern with tractional bronchiectasis and subpleural sparing with surrounding areas of fibrosis, consistent with fibrotic nonspecific interstitial pneumonia. 3) Small multifocal areas show the "atoll sign" with central ground glass opacity and thick-walled cysts, seen in conditions like bronchiolitis obliterans organizing pneumonia, especially in an immune compromised patient.

1. HRCT findings of
chest
By
Dr.S.Ranjith kumar
Ist year RADIOLOGY PG

2. HRCT Basic protocol
• High resolution CT is a
scanning protocol in which thin
sections (usually 0.625 to 1.25
mm) are acquired and
reconstructed using a sharp
algorithm (e.g. bone
algorithm).

3. Basic Interpretation of HRCT
chest

4. DIFFERENT PATTERNS IN HRCT
CHEST
• Secondary lobule
• Reticular pattern
Septal thickening
Honeycombing
• Nodular pattern
Algorithm for nodular pattern
Perilymphatic distribution
Centrilobular distribution
Tree-in-bud
Random distribution
• High Attenuation pattern
Ground-glass opacity
Mosaic attenuation
Crazy Paving
Consolidation
• Low Attenuation pattern
Emphysema
Cystic lung disease
Honeycombing
• Distribution within the lung
• Additional findings
• Differential diagnosis of interstitial lung diseases

5. Air-Space Nodule
A small, nodular opacity, usually ranging from
a few mm to 1 cm in diameter, that can be
seen in patients who have air-space diseases.
It represents a focal area of peribronchiolar
inflammation or air-space consolidation
Atelectasis
A reduction in lung volume either localized or
involving an entire lung, and often associated
with an increase in lung opacity or attenuation.
It may occur because of resorption of gas,
lung compression, deficiency of surfactant, or
fibrosis. Synonyms: collapse, volume loss
Bulla
A sharply demarcated area of emphysema,
measuring 1 cm or more in diameter and
possessing a wall less than 1 mm in thickness
IMPORTANT PATTERNS

6. Conglomerate Mass
A large opacity that often surrounds and encompasses
bronchi and vessels. It often represents a mass of fibrous
tissue or confluent nodules. It is most common in silicosis,
coal worker’s pneumoconiosis, and sarcoidosis
Cyst
A nonspecific term describing the presence of a thin- walled
(usually less than 3-mm thick), well-defined and
circumscribed, air- or fluid-containing lesion, 1 cm or more in
diameter that has an epithelial or fibrous wall
Dependent Opacity
An ill-defined subpleural opacity, ranging from a few mil-
limeters to 1 cm or more in thickness, that is only visible in
dependent lung regions and disappears when the lung region
is nondependent
Halo Sign
A halo of ground-glass opacity surrounding a nodule or mass.
It is nonspecific. It may be seen in patients who have invasive
aspergillosis (representing hemorrhage), other infections,
neoplasms

7. Headcheese Sign
A type of mosaic attenuation manifested by a
combination of patchy ground-glass opacity and
reduced lung attenuation as a result of mosaic
perfusion or air trapping. This pattern resembles the
heterogeneous appearance of a sausage
Peribronchovascular Interstitial Thickening
Thickening of the peribronchovascular interstitium that
surrounds the perihilar bronchi and vessels
This is recognizable by an apparent thickening of the
bronchial wall and an apparent increase in size or
nodular appearance of the pulmonary arteries
Subpleural Line
A thin, curvilinear opacity a few millimeters or less in
thickness, usually less than 1 cm from the pleural
surface and paralleling the pleura. This is a non-
specific term that may be used to describe dependent
opacity (a normal finding)

8. SECONDARY LOBULES
• Basic anatomical unit
• The interpretation of interstitial lung
diseases is based on the type of
involvement of the secondary lobule.
• Smallest lung unit that is surrounded
by connective tissue septa
• Secondary lobule is supplied by a
small bronchiole or terminal
bronchiole in the centre, which is
paralleled by the centrilobular artery
• The pulmonary veins and lymphatics
run in the periphery of the lobule
within the interlobular septa
Normal conditions only
a few of these
very thin septa
can be seen

9. AREAS OF LOBULE
Centrilobular area is the
central part of the secondary
lobule. Site of diseases, that
enter the lung through the
airways ( i.e.
hypersensitivity
pneumonitis, respiratory
bronchiolitis, centrilobular
emphysema ) [ Red arrow]
Perilymphatic area is the
peripheral part of
the secondary 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) [Green arrow]

10. Reticular pattern
• 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.
CAN BE TWO TYPES
1) SEPTAL THICKENING
2) HONEY COMBING
Retico nodular
pattern , with
bilateral PE (R>L) ,
Honey combing

11. SEPTAL
THICKENING
Thickening of the lung
interstitium by fluid, fibrous
tissue, or infiltration by cells
results in a pattern of reticular
opacities due to thickening of
the interlobular septa.
SMOOTH
NODULAR
Ignore IST unless its prominent
Think of IPE
Pulmonary edema
Fibrosis
Lymphatic spread of neoplasm

12. HONEY COMBING
Because of the cystic appearance,
honeycombing is also discussed in the
chapter on the low attenuation pattern
Honeycombing is defined by the
presence of small cystic spaces lined by
bronchiolar epithelium with thickened
walls composed of dense fibrous tissue
DD: Usual interstitial
pneumonia (UIP) , Idiopathic
pulmonary fibrosis , Silicosis
, RA , scleroderma , chronic
hypersensitivity pneumonitis
SUB PLEURAL
FIBROUS WALL

13. UIP
• AKA Idiopathic IP
• Usually a reactive a pertaining
to a previous insult
• Several patterns
• Inflammation and fibrosis
• Variable response to Rx
• Causes —- Idiopathic , drugs ,
Inhalation

14. NODULAR PATTERN
In most cases small nodules can be placed into one of three categories:
Perilymphatic, centrilobular or random distribution

15. SUMMARY
1) Look for pleural nodules
2) Look for central broncho
vascular interstitium
and interlobular septa

16. PERI LYMPHATIC NODULE
• Most commonly seen in
sarcoidosis
• Other diseases - Silicosis , Coal
workers Pneumoconiosis ,
Lymphatic spread of Ca
• Overlap of DD with reticular
pattern
• Thus this pattern can be called
“RETINO-NODULAR”

17. CENTRI LOBULAR
NODULES DISTRIBUTION
• CENTRO LOBULAR
distribution is usually seen in
disease that go through airway
• DD - Hypersensitivity
pneumonitis , respiratory
bronchiolitis , Infectious airway
disease , vasculitis
• Othername - ACINAR
NODULES

18. TREE IN BUD
APPEARENCE
• Usually centre lobular nodules
, multiple , branching ,
produces this pattern
• Occurs in disease that spread
through airway

19. RANDOM NODULES
SMALL RANDOM NODULES
ARE SEEN IN
Hematogenous metastasis
Miliary tuberculosis
Miliary fungal infection
LCH

20. HIGH ATTENUATION
PATTERN
• AKA Ground glass opacity if
there is a hazy increase in
opacity without obscuring
underlying vessels
• In both GGO ( does not have
AB , vessels visible in GGO
)and Consolidation ( Has AB,
vessels not visible) ,
IN SOME CASES
THERE IS BOTH

21. PROGNOSTIC FACTOR

22. MOSAIC PATTERN
• Used to describe density
differences between affected
and non affected areas , there
is patchy black and white lung
• GGO VS MOSAIC
CONCEPT
More blood supply more opacity/density
Less blood supply more translucency
Translucent areas are abnormal and areas
showing GGO have higher blood perfusion
CAUSES
Obstructive small airway disease
Occlusive vascular disease
Parenchymal disease

23. INCREASED DENSITY

24. LOW ATTENUATION
PATTERNS
• Emphysema
• Lung cysts
• Bronchiectasis
• Honey combing
Relatively easy to differentiate in HRCT has their
patterns are quite distinct

25. CENTRI LOBULAR
EMPHYSEMA
Most common type
Irreversible
Upper lobe
predominance
Smoking ++
PAN LOBULAR
Affects whole
secondary lobule
Lower lobe
predominance
In alpha 1 Antitrypsin
deficiency
Para septal
emphysema
Adjacent to pleura and
interloper fissure
Can be isolated
phenomena
In young adults often
associated with
pneumothorax
TYPES OF EMPHYSEMA IN HRCT

26. EMPHYSEMA VS LUNG
CYSTS
• Lung cysts are defined as
radiolucent areas with a wall
thickness of less than 4mm
• WALLS PRESENT
CYST VS CAVITY
Wall thickness less than
4mm in cystic lesions
And wall thickness more
than 4mm in a cavity
?
Multiple irregular
Shaped cysts , predominantly
Lower lobe

27. BRONCHIECTASIS
• Bronchiectasis is defined as
localised bronchial dilatation
• Bronchial dilatation (signet-
ring sign)
• Mucus retention in the
bronchial lumen
• Lack of normal tapering with
visibility of airways in the
peripheral lung
CYLINDRICAL VARICOSE CYSTIC

28. REVIEW OF ALL PATTERNS

29. RETICO NODULAR PATTERN
SEPTAL THICKENING WITH
GGO WITH DEPENDANT
DISTRIBUTION
SEPTAL THICKENING WITH
PATCHY GGO
GGO WITH SEPTAL THICKENING
(CRAZY PAVING)
CENTRILOBULAR
EMPHYSEMA
Lymphangitic carcinomatosis
with hilar adenopathy.
PATCHY AREA OF SEPTAL
THICKENING WITH GGO
IN DEPENDANT PORTION

30. CENTRI LOBULAR NODULES
PERI LYMPHATIC NODULES MILIARY NODULE
RANDOM

31. LYMPH NODES IN CHEST
1. Lower cervical
2. Upper para tracheal
3. Pre vascular and pre
vertebral
4. Lower para tracheal
5. Sub aortic
6. Pre aortic
7. Sub carinal
8. Para oesophageal
9. Pulmonary ligament
10. Hilar

33. DIAGNOSE
1
2
Reticular pattern
Involving the sub pleural
areas of superior segment of
lower lobes , some inter lobular septal
Thickening —— suggestive of UIP
Reticular pattern
With tractional bronchiectasis with sub pleural
sparing with surrounding areas of fibrosis
FIBROTIC NSIP

34. 3
4
UIP NSIP
Patchy and multi
focal area of thick
walled cysts with
central area of GGO
producing the Atoll
sign , BOOP

35. 5
6
Small multi focal Atoll sign , immune compromised , crytococcus pneumonia
IMMUNOCOMPROMISED
Diffuse area of GGO , with sub
pleural sparing , pre dominantly in
mid and lower lobes , bilateral ,
with acute onset, suggestive of
edema or proteinosis

36. 7
8
TREE IN BUD
INFECTIONS -TB , ABPA
GRANULOMTOUS - SARCOID
SILICOSIS
ASPIRATION
Diffuse GGo with patchy areas of
sparing probing the mosaic
attenuation noted bilaterally
involving all the segments , with
chronic onset , probably
eisonophilic or hypersensitivity

37. 9
10
Multiple cysts , round , all lobes,
Usually thin walled , diffuse , women ,
child bearing age
LYMPHANGIOMYOMATOSIS
Crazy paving
Acute - proteinosis , edema,
ARDS
Chronic - BOOP , radiation , GP
syndrome

38. THANK YOU