Presented by Dr. Radhika Ghongane KMC, Manipal

1. Computed tomography of thorax-
basics and its interpretation
BY - Dr Radhika
MODERATOR – Dr Rahul Magazine

2. INTRODUCTION
• CT is based on precise measurement of attenuation of
a thinly collimated x-ray beam
• Attenuation : reduction in the intensity of the beam
• occurs due to scattering and absorption of x-ray
photons by tissue
• Denoted by Hounsfield units

3. Types of CT-Scan

4. High resolution CT (HRCT) scan
• Performed using conventional CT scanner
• Imaging parameters are chosen to maximize spatial
resolution
• Takes widely spaced thin sections
• IV contrast are not used for HRCT
• Technique is unsuitable for assessment of the soft tissue
and blood vessels
Plain CT
HRCT

5. CT number (Hounsfield units)
•
𝑢−𝑢 𝑤𝑎𝑡𝑒𝑟
𝑢 𝑤𝑎𝑡𝑒𝑟
x 1000
• X-ray attenuation of each pixel is
normalized to that of a test object
containing pure water
CT number Tissue
−1000 Air
−700 to −900 Normal lung
−100 Fat
0 Water
20 to 60 Most soft tissues
+100 Blood clot
+1000 Bone

6. BASIC INTERPRETATION (Lung window)
1. Appearance/pattern
2. Location
3. Distribution
4. Additional findings

7. CT APPERANCE/PATTERN
• 4 categories :
1. Increased attenuation - Ground-glass opacity and consolidation
2. Decreased attenuation
3. Linear opacities
4. Nodular opacities

8. Ground glass opacity
• ACUTE CAUSES –
1. Pulmonary edema
2. Pulmonary haemorrhage
3. Pneumonia
• Increase in lung attenuation not obscuring underlying vessels
• Maybe physiological

9. Ground glass opacity
• CHRONIC CAUSES –
1. Organizing pneumonia
2. Pulmonary alveolar proteinosis
3. Bronchoalveolar carcinoma

10. Consolidation
• Homogenous opacities with obscuration of
pulmonary vessel
• Little/no volume loss
• Associated with air bronchogram
• Poorly defined margins
• HALO SIGN : Focal consolidation surrounded by GGO
Eg. aspergillosis

11. • Emphysema
• Bronchiectasis
• Sarcoidosis
• Hypersensitivity pneumonitis
• Vasculitis
Air-trapping
Decreased lung attenuation

12. Decreased lung attenuation
Cystic disease
• Lymphangioleiomyomatosis
• Langerhans cell histiocytosis
• Lymphocytic interstitial pneumonitis
• Pneumocystis pneumonia

13. CYLINDRICAL VARICOSE CYSTIC
Decreased lung attenuation
Types of Bronchiectasis

14. Reticular opacities
• Thickening of interstitial fibers of lung
by fluid, fibrous tissue or cells
CAUSES -
• ILD
• Pulmonary edema
• Lymphangitic spread of tumor
• Sarcoidosis

15. Nodular opacities
• Single/multiple
CAUSES -
• Malignancy
• Silicosis, CWP
• Endobronchial spread of infection
• Garnuloma
• Location- centrilobular, perilymphatic or random

16. Location
• Centrilobular
• Perilymphatic
• Random

17. 1. Centrilobular
• In or near the center of the secondary pulmonary lobule
• Spares pleural surfaces
• Indicative of endobronchial spread
1. Small airway inflammatory diseases - Poorly defined, poorly marginated GGO
2. Bronchiolar filling - Mucoid impaction in bronchioles

18. Centrilobular
BRONCHIOLAR FILLING;TREE-IN-BUDSMALL AIRWAY INFLAMMATORY DISEASES
(RB-ILD)

19. 2. Perilymphatic
• Within interstitial septa and
bronchovascular compartments
• Subpleural location, particularly in
relation to the fissures

20. • Lymphatic system involvement
1. Pulmonary interstitial edema
2. Sarcoidosis
3. Lymphangitic carcinomatosis
SUB-PLEURAL
PERI-BRONCHOVASCULAR

21. 3. Random
• Hematogenous dissemination of
metastases or infection
• Example - Miliary tuberculosis

22. DISTRIBUTION
• According to lobes –
1. Upper
2. Lower
3. Diffuse
• According to region –
1. Central
2. Peripheral

23. Upper lobe predominant
1. Langerhans cell histiocytosis
2. Sarcoidosis
3. Silicosis
4. Coal workers’ pneumoconiosis (CWP)
5. Tuberculosis
6. Cystic fibrosis
7. Centrilobular emphysema

24. Lower lobe predominant
1. ILD-UIP/IPF
2. Asbestosis
3. Organizing pneumonia
4. Alveolar haemorrhage
5. Pulmonary edema
6. Panlobular emphysema

25. Diffuse involvement
1. Hypersensitivity pneumonitis
2. Lymphangioleiomyomatosis
3. Lymphangitic spread of tumor

26. Central
1. Sarcoidosis
2. Silicosis
3. CWP
4. Lymphangitic spread of tumor
5. Pulmonary alveolar proteinosis

27. Peripheral
1. ILD-UIP/IPF
2. ILD-NSIP
3. Acute interstitial pneumonia
4. Hematogenous metastasis
5. Pulmonary embolism

28. Mediastinal window

29. Mediastinal window
Lymph node stations

30. Mediastinal staging

31. REFERENCES
• Fishman’s pulmonary diseases and disorders 5th edition
• Murray and Nadel’s textbook of respiratory medicine 6th edition
• Radiopedia.org

32. THANK YOU !