Fig. 51 is from one of our textbooks.
On one side  the calcifications of parietal and visceral pleura have been described correctly.
But the space between pleurae is suggested  to be "probably fibrotic”, because the author "measured” +45 -60 Hounsfield Units (HU).
It is uncertain whether densitometry is reliable in a scan with artefacts and in a region so close to bony structures. – Anyway, this rather high density provides no argument against liquid.
The diagnosis "probably fibrotic”  is nonsense.

Important findings as
- dislocation of the heart,
- the volume reduction of the right chest,
- pathology of ribs

are not described.
(See literature on densitometry.)

Pleural calcification Is not a harmless residual finding when – like it is here – it is associated with an underlying effusion. Personne’s long- term observations of persistent effusions with calcified pleurae indicate that fistulas communicating with the bronchial system or penetrating the chest wall developed in 66 out of 72 patients (91,2%).

An other worldwide misunderstanding concerns the uncalcified layer between the parietal calcified and inner thoracic wall. In many books it is interpreted as parietal pleura; concluding with the rule that parietal pleura would not calcify, visceral pleura would do so. This is nonsense.  It leads to a wrong understanding of pleural anatomy. Former (or persistent) pleural space is located in the incorrect way. -
Bare in mind: both pleurae can calcify.

Bild 51

nonsense of textbooks

56-year old man with bilateral tuberculous pleurisy 26 years earlier.
PA view shows simple calcified fibrothorax on the right side. There is no fluid separating the two pleural layers, which are either adherent to one another (due to fibrous adhesions) or simply lying adjacent to each other by a thin, uncalcified layer. – On the left side, a strikingly thick shadow with calcification of both the medial and lateral borders. Signs indicating a persistent effusion include the unusually thick pleural shadow, the presence of two calcified pleural layers, and formation of a cavity rather than obliteration of pleural space.

Bild 52

important case

CT scan reveals a large, globular collection of fluid restricted to the left pleural cavity. Both pleural layers are thickened and partially calcified. The density within the cavity (+34 HU) and the lack of enhancement suggest that the fluid is rich in protein. Do not overestimate the absolute HU values (artefacts) The uncalcified layer between the inner chest wall and the calcified parietal pleura shows absorption values of –80 to –100 HU, indicating that it is rich in fatty tissue. This layer allows some respiratory mobility.

Bild 53

CT persist effusion and simple fibrothorax

Synopsis PA view - CT.
The vertical lines represent the medial and lateral borders of the fluid-filled pleural cavity, e.g. the visceral and parietal pleurae. The lines project the borders from the axial scan (53) to the radiograph (52).

We do not need CT for the diagnosis. But it is a lot easier eliminating misunderstanding for people who are not familiar with pleural pathology.

Oblique shots or rotating fluoroscopy
are no longer necessary in  times of CT; but they might be very informative where CT is not available. Imagine you would turn the patient from PA - step by step -  to a LAO position: the calcification of inner and outer border is visible in every projection indicating the calcification goes round the whole mass (=effusion).

Bild 54

Pleura learn from CT for konvent

The shape of a residual effusion/chronic empyema is determined by the quantity of contents.
In simple calcified fibrothorax, both pleural layers are adjacent to each other (whether adherent or not). In case of persistent effusion, the pleural walls are separated. The border of the inner wall (visceral pl) is determined by the volume of the effusion (1-3).

Easy diagnosis: large content results in an inward convex pleural visceralis (2) as shown in 52-54. –
Next case is the outward convex visceral pleura.

Bild 55

diff shapes visceral pleura