Non-Calcified Pleural Plaques, Differential Diagnosis
1. Pleural Plaques – occur as thin, thick, smooth, irregular or lobulated in appearance and may also appear as a focal elevation off of the diaphragm.
2. Chest Wall Fat – occurring as extra-pleural chest wall fatty deposition in large patients, especially males, is common and often presents as smooth, in-profile, chest wall thickening. However occasionally overlapping face-on thickening and/or even irregular or lobulated appearances to the fat can occur. CT is necessary to differentiate fat from plaques. Note, however, one is often surprised on CT because chest x-rays are very poor at identifying small non-calcified and even calcified plaques, and as such, many more plaques may be identified on CT than what would be suspected on chest x-rays. Also, there can be both plaques and fat present simultaneously, and in many cases the thickening seen on the chest x-ray is in fact fat, but there are plaques that were not seen on the chest x-ray that show up on CT.
3. Apical Pleural Thickening – occurs associated with aging, prior tuberculosis or fungus infection or on a non-specific basis. If there are pleural and parenchymal changes at the lung apices and those are the only findings on the imaging study, especially on CT/HRCT, beware that this may not be asbestos caused. There can be an overlap and there are circumstances where plaques do occur that high, but in general parietal plaques spare the apices.
4. Intercostal Muscles – result in bulging into the chest cavity, especially on CT or HRCT involving the posterolateral aspects of the upper chest cavity.
5. Fibrotic Healing Adjacent to a Healed Rib Fracture(s) – can cause localized thickening of the chest wall mimicking a plaque.
6. Plate-like Atelectasis/Curvilinear Scarring – occurring along the lateral chest walls – thickening of the lung tissue caused by atelectasis or scarring when it occurs directly adjacent to the chest wall on CT as well as chest x-rays can on occasion mimic a focal area of non-calcified pleural plaquing.
7. Thickened Endothoracic Fascia – can occasionally occur. These are especially problematic when occurring along the posterior lower chest wall. It is always best to look for in profile pleural plaques on CT or HRCT along the inner margin of a rib as opposed to between ribs, since the endothoracic fascia and intercostal muscles sometimes bulge into the lung in the interspace between the ribs.
8. Interface Between the Extra-Pleural Chest Wall Fat and the Adjacent Pleura – can result in a very faint curvilinear higher density rim, which may be difficult to absolutely differentiate from a very thin pleural plaque. This is rare, but occasionally occurs.
9. Asbestiform Fiber-Caused Pleural Plaquing – from such fibrous minerals as Erionite and Zeolite, most common in Turkey, can give identical appearing parietal pleural plaquing.
10. Coalescence of Peripheral Subpleural Micronodules – seen in silicosis and/or coal workers’ pneumoconiosis can form “pseudo-plaques” with the conglomerate mass lying directly adjacent to the chest wall, mimicking plaque formation.
11. Non-Calcified Nodules – of any type especially the most statistically common granulomas, when directly adjacent to the chest wall, can mimic a non-calcified plaque.
12. Visceral Pleural Thickening Occurring With Advanced Interstitial Lung Disease – of any cause. When there is advanced interstitial lung disease peripherally, there is often associated visceral pleural thickening. This can mimic pleural plaquing especially on CT and HRCT, but it is usually relatively thin and very irregular in appearance as opposed to parietal pleural plaquing, which tends to be more smooth in its margins and more discretely outlined.
13. Loculated Pleural Effusion – not appearing diffuse, can mimic localized pleural thickening due to plaquing. Loculated pleural fluid in a fissure can also mimic fissural thickening or a mass.
14. Loculated Areas of Blood/Hemothorax – can look this way, if not diffuse after acute injury or surgery.
15. Loculated Areas of Pus/Empyema – can look this way, if not diffuse, due to tuberculosis or other lung infections breaking through the visceral pleura covering the lungs and spilling pus into the potential space between the chest wall and lung.
16. Benign or Malignant Tumors – including metastases, causing thickening of the chest wall, can mimic non-calcified pleural plaquing.
Calcified Pleural Plaques, Differential Diagnosis
1. Calcified Pleural Plaques – which can be visualized as a linear, curvilinear or irregular ringlike calcifications, which when face-on (en-face) on chest x-rays, can have a “Holly Leaf” appearance.
2. Apical Pleural Calcifications – often associated with prior tuberculosis/fungal infections or other causes, can mimic calcified parietal pleural plaques. There can be overlap; however, parietal pleural plaques in general, spare the apices. When there are pleural and parenchymal changes in the apices beware that this may not be asbestos-caused.
3. Calcified Granulomas or Calcified Micronodules of Any Cause – occurring directly adjacent to the chest wall can mimic plaques, especially on CT and HRCT.
4. Calcified Scarring Adjacent Healed Rib Fracture(s) – can mimic a pleural plaque. If the apparent calcified pleural thickening is limited and only at the location of the healed rib fracture, there is a more significant probability that this is related to prior trauma.
5. Calcified Asbestiform–Mineral Caused Pleural Plaques – due to fibrous minerals called Erionite or Zeolite, most commonly found in Turkey.
6. Calcified Pseudo-Plaques – of silicosis or coal workers’ pneumoconiosis can mimic calcified plaques on plain radiographs and CT/HRCT, when the conglomerate calcified micronodules lie directly adjacent to the chest wall.
7. Enhancing Vessels – can be seen snaking along in a longitudinal fashion, adjacent to the pleura in the extra-pleural fat looking like a thin elongated calcified plaque and/or an enhancing vessel end-on can look like a punctate calcification in a plaque. This is why contrast enhancement is not necessary and can be confusing in evaluating CT and HRCT scans of the chest in asbestos disease.
8. Dystrophic Calcifications within the Destroyed Interstitium that has Advanced Fibrosis – can be close enough to the chest wall that they can mimic fine calcified plaquing on CT and especially HRCT. Any cause of advanced interstitial lung disease, can have small punctate lung calcifications.
9. Partial Calcification of Diffuse Pleural Thickening – occurring after an empyema (pus pocket/infection) involving the chest cavity often seen with tuberculosis. These are usually more elongated and associated with blunting of the costophrenic angle, but occasionally can look, otherwise. In addition, a hemothorax secondary to chest surgery can also result in diffuse pleural thickening with calcifications over time. Again usually the calcifications are associated with obvious diffuse pleural thickening and the presence of a cardiac valve and/or sternal sutures or other evidence for chest wall trauma and often there is blunting of the costophrenic angle.
The above article is presented as a public service by Daniel Powers, M.D., B-Reader and Diagnostic Radiologist, certified by the American Board of Radiology.
If you detect any errors, have additional entries into the differential diagnoses or have comments, please do email them to me at firstname.lastname@example.org.