Radiological Criteria
A hole in the lung with a wall, lumen and contents. Focus of increased density whose central portion has been replaced by air.
The following characteristics help in the differential diagnosis.
Number:
Multiple bilateral cavities would raise suspicion for either branchiogenous or hematogenous process. You should consider:
- Aspiration lung abscess
- Septic emboli
- Metastatic lesions
- Vasculitis (Wegener's)
- Coccidioidomycosis, tuberculosis
Single cavity
- Primary lung cancer
- Post-traumatic lung cyst
- Many other diseases
Size:
A large cavity encompassing the entire lobe or lung should raise suspicion for gangrene of lung.
Location:
- Classical locations for aspiration lung abscess are superior segment of the lower lobes and axillary subsegments of anterior and posterior segments of upper lobes.
- Tuberculous cavities are common in superior segments of upper and lower lobes.
- When a cavity in anterior segment is encountered, a strong suspicion for lung cancer should be raised. TB and aspiration lung abscess are rare in anterior segments. Cancer lung can occur in any segment.
Wall Thickness:
- Thick walls are seen in:
- Lung abscess
- Necrotizing squamous cell lung cancer
- Wegener's granulomatosis
- Blastomycosis
- Thin walled cavities are seen in:
- Coccidioidomycosis
- Metastatic cavitating squamous cell carcinoma from the cervix
- M. Kansasii infection
- Congenital or acquired bullae
- Post-traumatic cysts
- Open negative TB
Lining of Wall:
The wall lining is irregular and nodular in lung cancer or shaggy in lung abscess . The appearance is akin to stalactites and stalagmites.
Contents:
- The most common cause for air fluid level is lung abscess. Air fluid levels can rarely be seen in malignancy and in tuberculous cavities from rupture of Rasmussen's aneurysm.
- A fungous ball should make you consider aspergillosis. A blood clot and fibrin ball will have the same appearance.
- Floating Water Lily: I have never seen this. The collapsed membrane of a ruptured echinococcal cyst, floats giving this appearance.
Associated Features:
Ipsilateral lymph nodes or lytic lesions of the bone is seen with malignancy.
Evolution of Lesion:
Many times review of old films to assess the evolution of the radiological appearance of the lesion extremely helpful. Examples
- Infected bullae
- Aspergilloma
- Sub acute necrotizing aspergillosis
- Bleeding from Rasmussen's aneurysm in a tuberculous cavity
Etiology:
Cavity can be encountered in practically most lung diseases.
Common diseases and their characteristics include:
- Primary Lung Cancer
- Thick wall
- Shaggy lumen
- Eccentric cavitation
- Necrotizing Pneumonia
- Lung abscess
- Gravity dependant segments
- Thick wall
- Air-fluid levels
- Tuberculosis
- Superior segments
- Infiltrate around
- Bilateral
- Fungal infections
- Aspergillus
- Fungous ball
- Sub acute invasive aspergillosis
- Metastatic disease
- Thin walled (Squamous cell)
- Thick wall (Adenoma)
Comprehension of the Above Principles:
- Rationale for multiple bilateral cavities.
- Why does reactivation TB occurs in superior segments?
- Why does aspiration lung abscess occur in the superior segment of lower lobes?
- What is the criteria for thick and thin wall ?
- What is the pathogenesis of stalactites and stalagmites?
- What is crescentic sign?
- How do you differentiate between aspergilloma and sub acute necrotizing aspergillosis?
- Does the location of cavity in a density have diagnostic significance?
- What is open negative TB?
- In metastatic disease, when do you get thin walled cavities and when do you get thick walled cavities?