Respiratory JC013: Abnormal Lung Shadow On Chest Radiograph: CXR, CT

Question 1

Focal lung lesions

Answer 1

1. Solitary pulmonary nodule (SPN: <3 cm) / mass (>3 cm)
   - Benign / Malignant
   - DDx: Lung cancer etc.
2. Lung cancer

Question 2

How to investigate SPN

Answer 2

**Previous CXR (2 years)?
1. Yes
—> Been there before (2 years) + No growth —> Benign
—> Interval growth —> Suscipious —> **CT scan

2. No
   —> **Bronchoscopy + Sputum analysis / **CT scan

Question 3

CT thorax

Answer 3

Aim:

1. Characterise lesion (benign / malignant)
2. Solitary / Multiplicity
3. ***Staging in malignant lesion

CT measures **density / **attenuation value of structures

***Hounsfield units (HU)
- Air: -1000 (i.e. very dark)
- Water: 0 (grey shade)
- Fat: -20
- Soft tissue: 30-50
- Calcification: >150
—> Compare the HU of the lesion to these standards —> Determine nature of lesion (E.g. Hamartoma: Fat containing nodule)

Question 4

***Nodule characteristics

Answer 4

1. Shape
   - Round / Lobulated
2. Margins
   - Smooth / ***Spiculated (尖刺growing from mass, malignant, ∵ irregular + rapid growth)
3. Calcification
   - Uniform, Central
   - Speckled (一點點), ***Eccentric (係埋一邊, non-homogenous, malignant)
   - Dense, homogenous
4. Fat
5. Cavitation
   - mostly contain air (others: fluid, fungus)
   - history and clinical presentation are important to narrow DDx
   - Abscess: pyrexia, cough, drug abuse history
   - Infarction (e.g. PE): haemoptysis, pleuritic chest pain, SOB
   - Tumour: weight loss, haemoptysis
6. Air bronchograms
   - phenomenon of air-filled bronchi (dark) being made visible by the opacification of surrounding alveoli (i.e. consolidated lung, grey/white)
   - alveoli can be filled with **fluid, **pus, ***tumours

Question 5

Contrast CT

Answer 5

• 2.5-5 mm sections through thorax (can best achieve 0.625mm)
• ***Volumetric (spiral) scans with IV contrast
  —> overlapping of tissue
  —> whole volume of tissue acquired (i.e. no gap)
  —> will not miss small things in between slices

Use:
- Enhance characteristics of nodules

Anxillary findings:

• Other nodules
• LN
• etc.

Question 6

***CT of nodule

Answer 6

Enhancement
—> ***>25 HU (↑ density ∵ vascularity of tumour, take up contrast) —> Malignant
—> ***15-25 HU —> Indeterminate
—> <15 HU —> Benign
—> No enhancement —> Benign

Question 7

Features of Benign nodule

Answer 7

1. Well circumscribed
2. Central + Uniform calcifications
3. Fat-containing
4. ***Minimal / No enhancement

DDx:

1. ***Granulomata (∵ TB)
   - small
2. ***Inflammatory / Infectious lesions —> go away with treatment
3. AV malformations, Pulmonary sequestration
4. ***Harmatoma (fat)
5. Adenoma

(***: common)

Question 8

Features of Malignant nodules

Answer 8

1. Ill-defined, ***spiculated margins
2. ***Eccentric calcification
3. ***Pleural retraction (nodules pulling on pleura causing fibrotic changes)
4. Enhancement (esp. ***heterogenous enhancement)
5. Heterogeneous

Question 9

Management of Indeterminate nodules

Answer 9

1. Close follow-up with CXR / CT (3-6 months) (most)
2. Biopsy (if suspicion index high enough)
   - Percutaneous
   - Transbronchial
   - Surgical
3. Resection

Question 10

Investigations of Lung cancer

Answer 10

1. CXR
   - lung mass
   - mediastinal widening

Further evaluation

2. Contrast CT scan
   - staging +/- biopsy (percutaneous)
3. **Bronchoscopy
   - **biopsy + ***BAL
4. ***Post-bronchoscopy sputum analysis
   - higher yield than pre-bronchoscopy

Question 11

Staging of Lung cancer

Answer 11

TNM staging (Universally accepted)

1. T: primary tumour
2. N: nodal involvement (malignant LN: round)
3. M: metastasis
   - Liver
   - Adrenal

Question 12

***Pancoast tumour

Answer 12

Aka Apical tumour

Clinical features:

1. Invade into **brachial plexus
   - Hard to be assessed by CT —> require **MRI (only scenario when MRI is used for lung cancer)
2. ***Horner’s syndrome
3. ***SVC syndrome
4. **Thoracic outlet syndrome
   - compression at the superior thoracic outlet involving compression of a neurovascular bundle passing between the anterior scalene and middle scalene. It can affect the **brachial plexus (nerves that pass into the arms from the neck), and/or ***subclavian artery or rarely the vein which does not normally pass through the scalene hiatus (blood vessels as they pass between the chest and upper extremity)

Question 13

CT evaluation of Lung cancer

Answer 13

Remains ***modality of choice for lung cancer staging

• Favourable cost
• Speed of examination
• Simultaneous evaluation of intrathoracic and ***abdominal organs

1. Stage disease
   - assess ***operability (inoperable if invaded to mediastinum)
2. ***Radiation planning
   - anatomic relationship
   - disease extent
   - surrounding tissue thickness
3. Assess treatment response

Pitfalls of CT:

1. Mediastinal LN
   - now can only rely on ***size criteria
   - inflammation (i.e. reactive LN) vs metastasis
   - microscopic metastasis
2. Indeterminate chest wall / mediastinal invasion

Question 14

Ancillary investigation

Answer 14

Flexible bronchoscope
- thin enough for direct visualisation of up to 6th generation bronchi (21 generations before alveoli reached)

• good for **Proximal lesion (central, close to hilum / main bronchi)
  —> **Saline washing and brushing: Microbiology + Cytology
  —> ***Biopsy under direct vision: Histology
• Peripheral lesion relatively difficult
  —> not visualised directly
  —> **BAL: Microbiology + Cytology
  —> **Percutaneous / ***Transbronchial biopsy: Histology

Question 15

Other staging techniques of Lung cancer

Answer 15

1. ***Mediastinoscopy + Biopsy
   - can assess chest wall / mediastinal invasion
2. Transesophageal USG + Biopsy
3. ***Thoracotomy + Nodal sampling
4. ***PET

Question 16

MRI of Lung cancer

Answer 16

Good for looking at ***soft tissues (esp. in Pancoast tumour)

1. Similar limitations to CT
   - ***Signal in lung is poor on MRI
2. Expensive
3. ***Pancoast / Superior sulcus tumours
4. Chest wall, ***Brachial plexus

Question 17

PET/CT of Lung cancer

Answer 17

• 18-FDG
• Make use of glucose metabolism —> ↑ metabolic activity (hot) —> identify Neoplasms
• False positive: **Inflammatory lesions, **TB

Advantages:

• Whole body scan —> detect ***occult metastases elsewhere (very sensitive)
• High sensitivity (90-95%)

Disadvantages:
- ***Lower specificity (false +ve)

Question 18

Diffuse lesions (vs Focal lesions e.g. Nodules)

Answer 18

Disease affecting:

1. Interstitium
2. Airspace
3. Small airways

Lesions:

1. ***Interstitial lung disease
   - Interstitial pulmonary fibrosis
   - Occupational lung disease
2. Infections
   - Pneumocystis pneumonia (PCP) / Pneumocystis carinii
   - TB
3. ***Bronchiectasis and Bronchiolitis
4. ***Emphysema

Question 19

Interstitial lung disease

Answer 19

• ***Reticular shadowing
• ***Volume loss (Fibrotic lungs)
• ***Shaggy heart borders
• Associated with Rheumatoid Arthritis

Question 20

High resolution CT

Answer 20

• Thin 1mm sections at 10mm interval (∵ looking at diffuse lesions, ∴ does not matter to miss small lesions vs Spiral CT)
• ***No need to give contrast (∵ not looking at focal nodules)
• ***High spatial resolution algorithm
• ***Reduce radiation
• ***Excellent for studying:
  1. Lung parenchyma
  2. Interstitium
  3. Airways

Aim in diffuse lesions:

1. Characterise disease
2. Determine ***extent of disease
   - upper / mid / lower
   - central / peripheral
3. ***Localise site for biopsy
4. Post-treatment evaluation

Question 21

Pneumocystis pneumonia

Answer 21

Ground glass appearance around hilum on HRCT

Question 22

Lymphangioleiomyomatosis

Answer 22

Associated with Tuberous sclerosis

• Cystic changes in lungs
• ↑ Lung volume

Question 23

Summary

Answer 23

Focal:

• Thin section / Contrast CT
• MR / PET

Diffuse: HRCT

If Biopsy required:
- Localise lesion with CT +/- Biopsy

Other ancillary investigations
- ***Bronchoscopy
- ***BAL
- ***Sputum analysis
- Mediastinoscopy
- ***Thoracotomy
- Biopsy:
—> Percutaneous
—> Transbronchial
—> Surgical