Imaging of asbestos-related lung and pleural diseases as an endemic exposure in Egypt

Asbestos refers to a group of naturally occurring silicate minerals which have been traditionally used in building materials and household products. Inhalation of asbestos fibers, however, has been associated with adverse health outcomes, with the disease manifestations principally affecting the thorax. The aim of our study is to detect and evaluate the different radiological patterns of asbestos-related lung and pleural disease and its complications MDCT examination was able to assess and distinguish asbestosis as well as asbestos-related lung and pleural disease besides detection of any associated complications. This study demonstrates that while reporting of malignant asbestos-related pleural disease is adequate, there is room for improvement in the reporting of more benign disease.

It has been clearly established that asbestos-related interstitial fibrosis (i.e., asbestosis) are associated with an increased risk of lung cancer, although asbestos-related lung cancer may occur in the absence of asbestosis. However, there is persistent controversy surrounding several aspects of asbestos-related diseases, particularly with respect to the consensus statement "workers with asbestos-induced pleural abnormalities are at increased risk for lung cancer compared with workers with similar exposures without these pleural abnormalities." Pleural plaques are the lesions most commonly observed among asbestos exposed subjects [4].
Health surveillance of formerly asbestos exposed individuals focus on early detection of asbestos-related diseases, such as lung fibrosis (asbestosis), pleural plaques, mesothelioma, and lung cancer in particular. One main concern is the early and clear identification of lesions with a high risk of malignant changes and their undelayed clinical work-up. False positive results may lead to unnecessary and often painful diagnostic interventions, which create high costs when applied to a large cohort and also may discredit the whole program [5].
Screening by low-dose chest computed tomography (CT) scan was associated with a significant reduction of lung cancer mortality in some current or former heavy smokers between the ages of 55 and 75 years with a smoking history of at least 30 pack-years (one pack-year equals smoking one pack [20 cigarettes] per day for 1 year) [4].

Methods
This prospective observation study was conducted on 40 patients (32 males and 8 females) with asbestos-related lung disease with an age range from 37 to 78 years mean ± 55.40 years.
Cases were referred to the radiology department for multidetector computed tomography (MDCT) assessment after obtaining required consents and were approved by the ethical committee in our department.
The complaints varied between dyspnea, chest pain, cough, hemoptysis, fatigue, and loss of weight.
Inclusion criteria This includes patients coming to the radiology department complaining of chest symptoms with history of asbestos exposure.
Exclusion criteria None. All cases were subjected to the following: Written consent and explanation of the technique and its aim Past medical history General asbestos exposure history: any direct contact with asbestos (source, intensity, and duration of exposure), age at first exposure, and years since first exposure Occupational exposure history

Protocol for MDCT
MDCT examination of the whole lung in supine position during one breath-hold with deep inspiration without administration of contrast material was applied (SOMA-TOM Sensation 16, Siemens Medical Solutions, Forchheim, Germany). A standard low-dose MDCT protocol was used: 120 kV, 10 mA for individuals with less than 80 kg, 20 mA for individuals with 80 kg and more, 16 × 0.75 mm collimation, rotation time 0.5 s, table feet/rotation 18 mm. Images were reconstructed in three different ways. Low-dose CT refers to scanning techniques which use tube current less than 100 mAs in an attempt to deliver reduced radiation dose to the patient while maintaining diagnostic quality images. The first stack of images was reconstructed with 5 mm effective slice thickness applying an increment of 4 mm with a medium smooth soft tissue convolution kernel (Siemens B30 kernel) window setting (center (C) = 80 HU, window (W) = 400 HU) for analysis of soft tissue, mediastinal, and pleural changes. The next stack of images was reconstructed as 1-mm-thick sections with a reconstruction increment of 0.5 mm and a sharp kernel (Siemens B50 kernel) (C = − 600; W = 1500) for detection of pulmonary nodules, and the last stack of images was reconstructed as a high-resolution set with 1-mmthick sections every 10 mm with a B80 ultra sharp  reconstruction kernel (C = − 600; W = 1500) for analysis of additional asbestos-related changes.

Image interpretation
Images were interpreted independently by three observers, two experienced in thoracic imaging (15-20 years' experience) and one novice. The inter-observer agreement was about 90%, and controversy was only in the list of findings.

Statistical analysis
All statistical calculations were done using computed program SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) release 15 for Microsoft Windows (2006).

Results
This study was conducted on 40 patients with asbestosrelated lung disease with the following results: The mean duration of exposure of asbestos was 22.73 years, and the mean time since first exposure was 23.75 years with a latent duration about 19.36 years (Fig. 1).
In this study, 40% of patients showed malignant lesions in the form of mesothelioma in 27.5% and bronchogenic carcinoma in 12.5% of cases, and benign lesions were found in 60% of cases in the form of calcified pleural plaques in 40%, pleural effusion in 7.5%, lung fibrosis in 7.5%, and round atelectasis in 5% (Figs. 2, 3, 4, 5, and 6).
Calcified pleural plaques were found in 32 cases (80%), of which 16 cases showed associated malignancy (40%) and 16 cases showed calcified pleural plaques only (40%) ( Table 1).   There were no statistically significant differences between the malignant and benign groups as regards smoking status (p value 0.237) as well as the presenting symptoms. However, there was a significant difference between the two groups as regards duration, time of exposure, and latent period as cancer susceptibility increases in patients with longer duration of exposure and longer latent period ( Table 2).
On univariate analysis, the significant factors affecting malignancy of lesions were duration of exposure and time since first exposure (Table 3).

Discussion
Asbestos-related disease is a worldwide problem. Pleural plaques (PP), asbestosis, malignant mesothelioma, pleural effusion, diffuse pleural thickening, and bronchogenic carcinoma constitute asbestos-related diseases with the pleural plaques being the most common manifestation. Detection of early pleural and parenchymal changes on computed tomography (CT) is more sensitive than chest X-ray [6].
In the present study, we aimed to detect and evaluate the different radiological patterns of asbestosrelated lung disease and its complication by including 40 patients with asbestos-related lung disease with mean age of the studied patients being 55.4 years with male predominance at 80%. Of patients, 55% were smokers, 30% were ex-smokers, and 15% were non-smokers.
In the current study, we found that the mean duration of asbestos exposure was 22.73 years and the mean time since first exposure was 23.75 years with a latent duration about 19.36 years.
In a study by Ahn et al. [7], they found that the mean duration of Asbestos exposure for the compensated workers was 16 years. The most common duration of exposure involved the group exposed to asbestos for 10-20 years (eight cases). The mean duration of the latency period was 22.6 years. The most common duration of the latency period was 20-30 years.
In the present study, we found that 40% of patients showed malignant lesions in the form of mesothelioma in 27.5% and bronchogenic carcinoma in 12.5% of cases. On the other hand, 60% showed non-cancer lesions in the form of pleural effusion in 7.5%, calcified pleural plaques in 40%, lung fibrosis in 7.5%, and rounded atelectasis in 5%. In a study by Çoşğun et al. [6], it was found that pleural plaques due to environmental asbestos exposure were found in 66 of the 75 patients on chest CT distributed as follows: 64 (96.6%) costal plaques, 44 (66.6%) diaphragmatic plaques, and 9 (13.6%) pericardial plaques.
Comparing patients diagnosed with malignant and benign lesions, there were no significant differences as regards age, sex, smoking status, and presenting symptoms.
As regards smoking status in contrary to our result, the bulk of epidemiologic evidence implicates asbestos as a carcinogen, the effect of which is augmented by cigarette smoking. A synergistic relationship between the two carcinogens is commonly accepted, and a review of 23 studies addressing smoking and asbestos exposure lends support to a multiplicative interaction [8].
Ιn a retrospective study of 98,912 asbestos workers, Frost et al. [9] demonstrated that the interaction between smoking and asbestos exposure was greater than the additive (i.e., multiplicative) to the occurrence of lung cancer, while lung cancer risk remained increased even 40 years after smoking cessation.   In the current study, we found that there were significant differences between the two groups as regards duration, time of exposure, and latent period as cancer susceptibility increases in patients with longer duration of exposure and longer latent period, and by univariate analysis, the significant factors affecting malignancy of lesions were duration of exposure and time since first exposure.
This was also detected by other studies as they revealed that the risk of malignant mesothelioma MM is very low in the first 10-15 years [10]. The mean latency period has been repeatedly found to be 30-40 years, and more than 90% of MM were diagnosed more than 15 years after the first asbestos exposure [11,12].
However, MM cases were reported with a very brief latency period and epidemiologic studies support the hypothesis that heavy asbestos exposure may result in a shorter induction period [13].
The consensus of international experts is that a minimum of 10 years from the first exposure is required to attribute MM to asbestos exposure [15]. This difference may be caused by a short history of occupational asbestos use and relatively younger compensated workers compared to other countries. For example, reviewing the series of 557 MM of the pleura in Italy, latency period ranged from 14 to 75 years (mean, 48.8 years; median, 51.0 years) [14].
Moreover, Mastrangelo et al. [16] showed that a significant increase in asbestos risk was found with increasing cumulative asbestos exposure, but not with time since first exposure, peak exposure, duration of exposure, age, and smoking. It can be seen that the significant risk factors were cumulative exposure to asbestos, time since first exposure and peak exposure for pleural plaques, and time since first exposure for diffuse pleural thickening.

Conclusion
This study demonstrates that while reporting of malignant asbestos-related pleural disease is adequate, there is room for improvement in the reporting of more benign disease.