Lung masses

Lung anatomy
- Primary lung lobule
  - Not so important in radiology
- Secondary lung lobule
  - Represent a cluster of up to 30 acini supplied by a common distal pulmonary artery and bronchiole
  - Have polyhedral shape
  - Bounded by intralobular septa
    - Are visible as Kerley B lines in pulmonary oedema
Lung mass < 3 cm = nodule
Lung mass > 3 cm = mass
Modalities
- X-ray
- CT
- PET
Benign vs malignant
- Characteristics of benign masses
  - Age < 40
  - Small (< 3 cm)
  - Round
  - Well-defined edges
  - Slow growth over time (years)
    - Comparison with older images is important!
  - Solid
  - Central, laminar or diffuse calcification
- Characteristics of malignant masses
  - Age > 40
  - Large (> 3 cm)
  - Irregular shape
  - Poorly defined edges
  - Obvious growth over time
  - Cavitated
  - Active accumulation of FDG on PET scan
Indirect signs of lung mass
- Atelectasis
- Postobstructive pneumonia
- Pleural effusion
- Hilar adenopathy
High risk
- Smoker
- > 40 years
- Clinical symptoms suspicious of cancer
  - Haemoptysis
  - Weight loss
  - Hoarseness
- Mass has malignant characteristics on imaging
If mass and/or patient is high risk -> investigation
- CT
  - Also for small peripheral lung masses
- PET
- Biopsy
Differential diagnosis
- Granuloma
  - TB
  - Histoplasmosis
- Hamartoma
- Primary lung cancer
  - Usually solitary nodule
  - Adenocarcinoma
    - Peripheral mass
  - Squamous cell carcinoma
    - Central mass
  - Small cell carcinoma
    - Hilar mass
- Metastases
  - Usually multiple nodules
- Round pneumonia
If tumor in apex of lung = Pancoast tumor
Multiple lung nodules must always be examined with CT

Mediastinal tumours

Many tumours can originate from or spread to the mediastinum.

Anterior mediastinum
- Thymoma (most common)
- Germ cell tumours (teratoma, seminoma)
- Lymphoma
- Substernal thyroid tumour or goitre
Middle mediastinum
- Developmental cysts (bronchogenic, pericardial, etc.)
- Lymphoma
- LN metastases
Posterior mediastinum
- Neoplasms arising from nerve sheaths, like neurofibroma (most common)
- Neoplasms arising from sympathetic ganglia, like neuroblastoma
- Neoplasms arising from paraganglionic tissue, like paraganglioma

The most common mediastinal mass is involvement of the mediastinum by bronchogenic lung cancer.

The "4 T’s of mediastinal masses"

Thymoma
Teratoma
Thyroid neoplasm
“Terrible” lymphoma

Clinical features

Mediastinal masses are frequently asymptomatic, only discovered incidentally on imaging. However, they can also cause a variety of different symptoms:

Dysphagia
Airway compression
Hoarseness – due to affection of recurrent laryngeal nerve
Elevated hemidiaphragm – due to affection of the phrenic nerve
Horner syndrome – due to affection of the sympathetic chain
Superior vena cava syndrome
Haemoptysis

Thymoma is frequently associated with myasthenia gravis, and patients diagnosed with thymoma should be evaluated for this.

Diagnosis and evaluation

X-ray (both AP and lateral) is the best initial test for mediastinal disorders, and may show a widened mediastinal shadow. It should be followed up by a contrast CT scan if any masses are found. The CT can give information on the density of the mass, which is important for the differential. If a malignancy is suspected, PET/CT should be made.

The final diagnosis requires histology, and so a biopsy is required. This can be achieved by transcutaneous FNAB, bronchoscopy, mediastinoscopy, endoscopic (oesophageal) ultrasound, thoracoscopy, or by thoracotomy.

Treatment

Almost all mediastinal masses are indications for surgical removal. One exception is the seminoma, which is highly sensitive to chemo and radiotherapy and is therefore not operated. Another exception are the cysts, which are only operated if they’re growing or causing symptoms.