Teaching Case

An asymptomatic 76-year-old man with left lung nodular opacities and pleural space shadowing demonstrated on a chest X-ray underwent thoracic CT for further characterization. Past history of extensive left pneumonia was noted.

Chest X-ray showed two nodular opacities in the periphery of the left lower zone and pleural shadowing over the middle and lower zones on the same side (figure 1). Unenhanced thoracic CT was performed, and demonstrated a smooth and diffuse pleural thickening >3mm extending more than 8 cm craniocaudally and 5 cm laterally (Fig. 2 and 3). Nodular opacities seen in the chest X-ray corresponded to areas of round atelectasis (Fig. 4). After careful scrutiny of the medical records, a previous chest CT was retrieved, confirming the stable appearances of the pleural thickening and round atelectasis (not shown).

Benign diffuse pleural thickening (BDPT) results from a fibrosing process of the visceral pleura with fusion to the parietal pleura over a wide area [1]. The pathophysiological mechanism is thought to be an intense and continuous inflammatory insult that drives an excessive deposition and abnormal turnover of fibrinous matrix in the pleural space, which in turn becomes obliterated and fibrosed [1].
CT criteria fulfilment implies visualization of a continuous and smooth sheet of pleural thickening of >3mm extending for more than 8 cm craniocaudally and 5 cm laterally [2, 3]. BDPT usually extends along the posterior and lateral surfaces of the lower hemithorax, and sometimes is accompanied by parenchymal bands or foci of round atelectasis [4]. Almost always there is blunting of the costophrenic angles and volume loss on the affected lung [5]. Thickening >10mm, nodular thickening, and mediastinal pleural involvement are findings not usually associated with BDPT and should raise concern for malignancy (such as mesothelioma) [4].
Multiple aetiologies of BDPT are recognized, such as infection (including tuberculosis), haemothorax, asbestos exposure, collagen vascular diseases (notably systemic lupus erythematosus and rheumatoid arthritis) and thoracic irradiation [5].
Since it can be a cause of significant restrictive lung disease, some authors recommend follow-up for BDPT patients with physical examination, chest imaging and pulmonary function tests to monitor and manage deteriorations of the lung function [6].