Bronchogenic Carcinoma - Imaging & Radiology

Overview of Imaging Approach

1. Peripheral tumours
2. Central tumours (arising in a large bronchus at or close to the hilum)
3. Staging intrathoracic spread

1. Peripheral Tumours

Tumour Shape and Margins

Cavitation

• Can occur in tumours of any size; best demonstrated by CT
• Squamous cell carcinoma is the most likely cell type to cavitate
• Wall: irregular thickness, usually ≥8 mm thick; may contain tumour nodules
• Fluid levels are common

Calcification

• Rarely seen on plain chest radiograph
• Identified on CT in 6-10% of cases
• May represent pre-existing calcified granuloma engulfed by tumour, or dystrophic tumour calcification
• Most calcified tumours are large (≥5 cm diameter)

Other CT Findings

• Air bronchograms and bubble-like lucencies (pseudo-cavitation) - especially adenocarcinoma
• Ground-glass attenuation (GGA): associated with greater malignancy risk; more common with adenocarcinoma (may present as purely GGA nodule)
• Bronchocele/mucocele: dilated mucus-filled bronchi distal to an obstructing carcinoma

2. Central Tumours

• Collapse/consolidation of the lung beyond the tumour
• Hilar enlargement

Collapse/Consolidation - Key CT Signs

1. A soft-tissue density within a collapsed or consolidated lobe, separate from the normal vessels and bronchi
2. Irregular or tapered bronchial narrowing or cut-off (vs. smooth compression from extrinsic causes)
3. A visible mass with irregular stenosis of a mainstem or lobar bronchus
4. Enlarged central nodes on CT/MRI (simple pneumonia rarely causes radiographically visible hilar adenopathy)
5. Mucus-filled dilated bronchi within collapsed lobes on CT: branching tubular low-density structures - should prompt search for a centrally obstructing tumour

3. Staging Intrathoracic Spread

Hilar Enlargement on CXR

• May reflect a proximal tumour, lymphadenopathy, consolidated lung, or a combination
• A "dense hilum" sign: mass superimposed on the hilum increases density due to summation - may be the only indication of lung cancer on frontal CXR
• Must always inspect the lateral radiograph when a dense hilum is suspected

Mediastinal Invasion

• CXR: phrenic nerve paralysis (high hemidiaphragm) - but caution: lobar collapse, sub-pulmonary effusion, and diaphragmatic eventration can mimic this
• CT/MRI signs: visible tumour deep within mediastinal fat, especially if surrounding mediastinal vessels, oesophagus, or proximal mainstem bronchi
• Criteria suggesting resectability (Glazer criteria):
  • <3 cm contact with the mediastinum
  • <90° circumferential contact with the aorta
  • A visible mediastinal fat plane between mass and vital mediastinal structures
• Even clear-cut contact is not enough for diagnosis of invasion; apparent interdigitation can be misleading

Pleural Effusion

• CT/MRI density measurements for distinguishing malignant vs. reactive pleural fluid have not proven useful
• PET may have a role in evaluating pleural effusion

PET/CT in Nodal Staging

• CT limitations: poor specificity for nodal involvement - enlarged nodes may be reactive, due to coincidental benign disease, or associated consolidation/atelectasis
• Positive PET does not obviate need for histological confirmation of nodal involvement
• Negative CT + negative PET: very high likelihood that mediastinal nodes are clear - surgical resection can proceed without invasive mediastinal staging

Imaging Modality Summary

Summary of Staging Decision Algorithm

1. If CXR + CT ± PET show no spread beyond the lung (other than to ipsilateral hilar nodes) and bronchoscopy confirms resectability → proceed to surgical resection
2. Spread to ipsilateral nodes: adverse prognosis, but surgery not necessarily precluded
3. Biopsy confirmation of neoplastic nodal involvement (mediastinoscopy, mediastinotomy, or needle aspiration) is usually required before denying surgery to a patient with enlarged nodes on CT

• Grainger & Allison's Diagnostic Radiology, Chapter 8 (Thoracic Imaging Features of Bronchial Carcinoma)