Sir,
A 63-year-old male who was undergoing preoperative evaluation was referred for an abnormal chest radiograph with multiple calcific opacities. He did not give any history of having pulmonary tuberculosis in the past. He had no respiratory symptoms. He gave history of working in an asbestos factory for 5 years around 20 years ago.
Chest radiograph showed multiple bilateral calcified pleural plaques with sparing of both costophrenic angles [Figure 1]. This irregular thickened nodular edge of calcified pleural plaques had the appearance of a holly leaf [Figure 2], so called “holly leaf sign.”[1] “Geographic density” is another common term used to describe this appearance.
Figure 1.
Chest radiograph shows irregular thickened nodular edges of calcified pleural plaques resembling holly leaf. Costophrenic angles and apices are spared
Figure 2.
Holly leaf showing typical margins
Radiologically, asbestos pleural plaques are usually seen bilaterally in 80% of cases. They are focal areas of pleural thickening generally affecting parietal pleura mostly seen on posterolateral chest wall between the seventh and tenth ribs, lateral chest wall between the sixth and ninth ribs, the dome of the diaphragm (virtually pathognomonic) where they follows rib contour and diaphragm.[2] Sometimes, they enter lobar fissure and invade mediastinal pleura. Both apices and costophrenic angles are typically spared. Calcification is seen in approximately 5%–15% of patients.[3]
Computed tomographic (CT) scan is more sensitive for visualization of anterior and paravertebral plaques that are not well demonstrated at chest radiography [Figure 3c].[3] Diaphragmatic pleural plaques have a variety of contours [Figure 3b], but a classic example is a protuberance resembling a mushroom cap [Figure 3a] which is virtually diagnostic of prior asbestos exposure.
Figure 3.
Diaphragmatic pleural plaques (b) having a protuberance resembling a mushroom cap which is diagnostic of asbestos exposure. (a) Anterior and paravertebral plaques that are not visualized on a chest radiograph (c)
Asbestos exposure causes wide range of pulmonary manifestations, benign, being pleural plaques, pleural effusion, asbestosis, and malignancies such as lung cancer and malignant mesothelioma. Pleura is more sensitive than parenchyma for asbestos exposure.[3]
Pleural plaques are the most common manifestation of asbestos exposure. They serve as a marker for exposure and are not usually associated with symptoms or functional impairment. In general, plaques can be detected on chest radiograph, 20 years from initial exposure.[4]
Exact pathogenesis of pleural plaques formation is unclear. Most accepted theory is thought that fibers reach the pleura via subpleural lymphatic channels. Later on, it causes local inflammatory reaction and eventually fibrosis.[3] At histologic analysis, pleural plaques consist of relatively acellular bundles of collagen in “basket weave” pattern and may contain asbestos fibers, but asbestos bodies are absent.[4]
The differential diagnosis for pleural plaques should include adipose tissue, rib fracture, companion shadows for ribs, and other pleural masses such as metastases.[2]
Asbestos pleural plaque being a marker of asbestos exposure is used for medical surveillance and worker compensation claims. Asbestosis rarely occurs in the absence of pleural plaques; hence, pleural plaques in a patient with interstitial lung disease may provide a clue in making the diagnosis of asbestosis whenever patient does not give history of known asbestos exposure.[3] Pleural plaques may be an independent risk factor for lung cancer death in asbestos-exposed workers and could be used as an additional criterion in the definition of high-risk populations eligible for CT screening of lung cancer.[5]
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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