Of course, the cause has to be TUBERCULOSIS in our country !

esp, in view of the left lower zone infiltrates.

However, three close differentials exist for similar thick walled upper lobe cavities -

1.bronchiogenic carcinoma

2.lung abscess (esp kleibsella and sometimes staphylococcal)

3.mucormycosis (in diabetics)

 All three can have almost the same appearance.

(The solid content representing necrotic tumour, inspissated pus and mycetoma respectively)
A cavity forms only when there is communication between a destroyed lung and bronchus.

Settings in which a cavity can occur - 

1.Infection -

-Tuberculosis is the most common cause of cavity in our country.

-Can occur in severe forms of bronchopneumonia.

-Can occur as a sequele of lung abscess.

-Cavitation usually does not occur in uncomplicated lobar pneumonia. ( bcos here only inflammation occurs and no necrosis) However, if complicated by arteritis, apurtid necrosis and cavitation can occur.

2.Infarcts and laceration - cavitation usually does not occur unless secondary infection develops. (bcos of absence of a well marked communication between the involved area and a bronchus)

3.Bronchogenic carcinomas - cavitation frequently occurs. (bcos invasion, necrosis and
secondary infection inevitably occurs, and easy communication with bronchus)

4.Lung metastases - cavitation is rare. ( growth by expansion and not invasion, so less 
necrosis and secondary infection, no communication to bronchus)

 

CXR of the pt after 5months of AKT. (The cavity disappeared ! )

A cavity forms only when there is communication between a destroyed lung and bronchus.
When the communication is occluded, air in the cavity is absorbed, walls of cavity 
approximate, and later fuse, and cavity disappears.

Other Imp points :

Air fluid level is pathognomic of cavity.

-In cases where cavity is obscured by other shadows (thickened pleura/ pl.eff./consolidation/infiltration/ fibrotsis), air fluid level can be demonstrated by a BUCKY film.

-Cavities are usually located in lung periphery, adjacent to some interlobar fissure. 
Even cavities appearing near to the hilum are usually peripheral -anteriorly or posteriorly.

-PSEUDOCAVITY - A cavity may be simulated by overlapping shadows of blood vessels, usually near lung root. However,the wall cannot be traced along the entire circumference. If doubt - oblique view.