Lung mass imaging

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2] Akshun Kalia M.B.B.S.[3]

Overview

CT scan is the method of choice for imaging of lung mass. On imaging, the evaluation of lung mass will depend on several characteristics, such as calcification, margins, location, distribution, and attenuation. Further evaluation of lung mass should include other diagnostic studies such as bronchoscopy, sputum cytology, or mediastinoscopy. For occult disease and assessment of malignancy, additional tests such as PET scan may also be done.

Imaging

On imaging, lung mass can be divided into the following two categories:

1. Hyperdense Pulmonary Mass

• Hyperdense pulmonary mass is defined as a pulmonary mass with internal calcification.
• The most common causes of hyperdense pulmonary mass are granuloma (most common), pulmonary hamartoma, bronchogenic carcinoma, carcinoid tumors, and pulmonary metastases.

2. Cavitating Pulmonary Mass

• Cavitating pulmonary mass is defined as a gas-filled area of the lung in the center of a nodule, mass, or area of consolidation.
• Cavitating pulmonary mass is also characterized by a thick wall (must be greater than 2 - 5 mm).
• The most common causes of cavitating pulmonary mass include malignancies, infections, inflammation processes, and congenital malformations.

• The table below summarizes the most common causes of cavitating pulmonary mass:

Cavitating causes	Conditions	Description
Malignancy	Primary bronchogenic carcinoma (especially squamous cell carcinoma) Cavitating pulmonary metastases (especially squamous cell carcinoma, gastrointestinal adenocarcinoma, sarcoma)	Thick wall Irregular shape Causes distortion of adjacent structures
Infection	Pulmonary bacterial abscess/cavitating pneumonia Empyema Post-pneumonic pneumatocele Septic pulmonary emboli Pulmonary coccidioidomycosis Pulmonary actinomycosis/thoracic actinomycosis Pulmonary nocardiosis Melioidosis Pulmonary cryptococcosis	Abscess: Round in all projections Abruptly interrupts bronchovascular structures May form an acute angle with the costal surface/chest wall Abscesses have thick irregular walls Abscesses usually have an acute angle (claw sign) Empyema: Smoother margins Lentiform shape Distort and compresses adjacent lung Empyema has obtuse angles
Non-infectious	Granulomatosis with polyangitis Rheumatoid nodules	May be single or multiple Size ranges from 0.5 - 7 cm
Vascular	Pulmonary infarct	Consolidation with internal air lucencies "Bubbly consolidation"; this represents non-infarcted aerated lung parenchyma
Trauma	Pneumatoceles	Smooth inner margins Contain little if any fluid Wall (if visible) is thin and regular Persist despite absence of symptoms
Congenital	Congenital cystic adenomatoid malformation (CCAM) Pulmonary sequestration Bronchogenic cyst	Radiological features vary according to the disease

Imaging Evaluation

The evaluation of lung mass depends on the following 5 characteristics:

• Calcification: Calcification patterns are commonly seen in granulomatous disease and hamartomas. They are normally a sign of benign lung mass. The characteristic benign calcification patterns of lung mass include:
  • Diffuse
  • Central
  • Laminated
  • Popcorn
• Size: Any area of pulmonary opacification that measures more than 30 mm (3 cm) has to be evaluated to determine the histology of the tissue.
• Location: Common locations of lung mass are pleural, endobronchial, and parenchymal.
• Margins: The different types of margins for lung mass include lobulated or scalloped margins and smooth margins. The lobulated or scalloped margins are associated with intermediate malignancy probability whereas smooth margins are associated with benign nature of lung mass.
• Attenuation: Lung mass may have different types of attenuation. Common types of attenuation are solid (malignancy rate of only 7%), calcified, partly solid (malignancy rate of 63%), and ground glass (malignancy rate of 18%).