Diagnosis is not easy. An interesting situation: we have two and three lines running parallel to the chest wall. One line is typical for simple pleural scar.
Remember: “more than one” line is suspicious.

This 30-year-old man was presented with dyspnoea. He had suffered a penetrating chest injury 9 years earlier and had been hospitalised off and on with recurring bloody effusions on his left side. Drainage therapy had not been sufficiently well carried out. -
For the past 5 years the incorrect diagnosis of “calcified fibrothorax” was made on the basis of standard PA views.
The pleural shadow is unusually thick for simple fibrothorax  and contains several axial lines. These are an indication of a persistent mantle-shaped effusion. Pleural puncture at 5 cm met resistance; beyond this depth a clear, protein-rich fluid collection could be delivered; it  was partially replaced by air.

We are familiar with two lines running parallel to the inner chest wall. Where does this mysterious third line come from?
What is the horizontal line between the two points?
How thick is the cavity?
What is the opacity ?
See next picture for answers!

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years after empyema

Fluoroscopy revealed that the third line was far more of a dorsal one in nature (3). It is the projection of the tangential envelope-fold of the parietal to the visceral pleura.
Resulting from puncture and partial filling with air there is a partial sero-pneumotharax; the fluid level (curved arrow) is clearly visible.
The “simple bar” marks the axial diameter of the residual cavity;
the double bar marks the “famous” uncalcified layer between  pleura parietalis and inner chest wall.

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explain all dimensions
What could be a summary for this instructive case?
(Click here for the answer)

-pleural calcification can be seen in a radiograph (in most cases) only on a tangential projection. Depending on the shape of the cavity and the projection, two, three or even four shadow lines may be seen.

-The shadow produced by the persistent effusion is the result of the fluid rather than the result of the thin calcified layers.

This is the case of a patient, who suffered from specific pleurisy 36 years earlier as a 25-year-old man. The volume of effusion is larger than it was in
the previous case, but not as big as 52-54.

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chron empyema calc walls
What do the little points mark?
(Click here for the answer)

Within the large pleural shadowing  three calcified lines are marked running parallel to the thoracic wall. The inner and outer contour of rib is marked too.
To continue with this patient.

Little rotation in the direction of LAO-position.

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little rotation
What has changed in the picture? What remained unchanged?
(Click here for the answer)

The large mass lesion is unchanged. The small uncalcified layer inside the inner contour of ribs hasn’t changed.
There is, however, a change in the distance and relative distance of the three calcified bands.
This is a typical finding for empyemas of this shape in rotating fluoroscopy. In CT (next), it is easier to understand.

CT: large effusion enveloped by both calcified pleurae. We understand the different results in fluoroscopy-projections:
in different rotations parietal pleura has only been tangentially projected once; depending on the projection waved visceral pleura presents differently: two or one shadow line or no shadow at all.

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calc parietal and visceral pleura