Atlas iconographique tomodensitométrique des pathologies bénignes de l’amiante

[Compensation of occupational diseases during monitoring of the ARDCO cohort]

INTRODUCTION

Questions concerning under-reporting of occupational diseases (OD) linked to asbestos exposure are regularly voiced in France. Monitoring of the French multicenter Asbestos-Related Disease Cohort (ARDCO), which ensures post-occupational medical surveillance of subjects having been exposed to asbestos, provides information on (1) the medico-legal steps taken following screening by computed tomography (CT) for benign thoracic diseases, and (2) recognition of OD as a causal factor in malignant diseases.

METHODS

OD recognition - and possible compensation - was analyzed in July 2021 among 13,289 volunteers in the cohort recruited between 2003 and 2005.

RESULTS

Fifteen percent of the subjects in the cohort were found to have at least one recognized asbestos-related OD (78.2% benign pleural disease, 10.3% asbestosis, 14.2% lung cancer, and 6.0% mesothelioma). Only 58% of pleural plaques reported by the radiologist who performed the CT resulted in their recognition as ODs. On a parallel track, 88.7% of the mesotheliomas identified based on French National health insurance data and 46.9% of lung cancers were recognized as ODs.

CONCLUSIONS

This study confirms the feasibility of a system designed to facilitate recognition, leading to possible compensation, of asbestos-related occupational diseases. The system could be improved by better training of the medical actors involved.

[Evaluation of permanent disability levels in occupational pulmonary diseases]

Compensation for occupational pulmonary diseases requires the establishment of guidelines based on standardized and objective criteria, in order to provide compensation that is as fair as possible to patients who suffer from them. A review of the elements necessary for the examination of an individual file was carried out by a working group. It is accepted that respiratory functional exploration is the key element in assessing the level of permanent disability in all of these conditions, with the exception of thoracic malignancies. Guiding scales have been developed for the respiratory impairment of three types of conditions: occupational asthma, thoracic malignancy, and other respiratory diseases. Additional criteria for increasing the permanent disability level are also proposed in order to take into account professional prejudice, in particular the possibility or not of continuing the occupational activity, in the same job or after changing to another. For certain respiratory diseases, a periodic reassessment of the initially attributed permanent disability level is recommended as well as the initial one at the time of definitive cessation of occupational activity.

3-Dimensional Quantification of Composite Pleural Plaque Volume in Patients Exposed to Asbestos Using High-resolution Computed Tomography: A Validation Study

RATIONALE

As pleural plaque has been reported as a risk factor in the occurrence of lung cancer and mesothelioma, a reproducible and precise method of measurement of pleural plaque volume (PPV) is needed to further describe these relationships. The aim of the study was to assess the reproducibility of a 3-dimensional computed tomography (3D-CT) volumetric analysis of PPV in patients with occupational exposure to asbestos.

MATERIAL AND METHODS

A total of 28 patients were retrospectively randomly selected from the multicenter APEXS (Asbestos Post Exposure Survey) study, which was held between 2003 and 2005. All patients underwent a 3D-CT scan. Two readers specialized in chest radiology completed the 3D semiautomated quantification of lung volume using dedicated software. They also had to categorize the visual extent of pleural plaque in terms of thickness and circumference. Reproducibility of the continuous PPV variable was assessed using the intraclass correlation coefficient (ICC) and Bland-Altman analysis. Reproducibility of categorical variables was assessed using the κ test.

RESULTS

Intraobserver reproducibility of PPV was almost perfect (ICC=0.98 [95% interval: 0.97-0.99]), and interobserver reproducibility was very good (ICC=0.93 [0.88-0.97]). At Bland-Altman analysis, the mean differences were 0.1 (limit of agreement: -11.0 to 11.2) and 3.7 cc (-17.8 to 25.2), respectively. Visual analysis of both plaque in terms of thickness and circumference were fair to moderate, with κ values ranging from 0.30 to 0.60.

CONCLUSIONS

3D semiautomatic quantification of PPV is feasible and reproducible using CT in patients with occupational exposure to asbestos. PPV measurement may be useful to correlate with other asbestos-related disease outcomes and prognosis.

Focal pleural thickening mimicking pleural plaques on chest computed tomography: tips and tricks

Diagnosis of pleural plaques (PPs) is commonly straightforward, especially when a typical appearance is observed in a context of previous asbestos exposure. Nevertheless, numerous causes of focal pleural thickening may be seen in routine practice. They may be related to normal structures, functional pleural thickening, previous tuberculosis, pleural metastasis, silicosis or other rarer conditions. An application of a rigorous technical approach as well as a familiarity with loco-regional anatomy and the knowledge of typical aspects of PP are required. Indeed, false-positive or false-negative results may engender psychological and medico-legal consequences or can delay diagnosis of malignant pleural involvement. Correct recognition of PPs is crucial, as they may also be an independent risk factor for mortality from lung cancer in asbestos-exposed workers particularly in either smokers or former/ex-smokers. Finally, the presence of PP(s) may help in considering asbestosis as a cause of interstitial lung disease predominating in the subpleural area of the lower lobes. The aim of this pictorial essay is to provide a brief reminder of the normal anatomy of the pleura and its surroundings as well as the various aspects of PPs. Afterwards, the common pitfalls encountered in PP diagnosis will be emphasized and practical clues to differentiate actual plaque and pseudoplaque will be concisely described.

Chest CT scan screening for lung cancer in asbestos occupational exposure: a systematic review and meta-analysis

OBJECTIVE

Lung cancer is the most frequent malignant asbestos-related pathology and remains the most fatal cancer of industrialized countries. In heavy smokers, early detection of lung cancer with chest CT scan leads to a 20% mortality reduction. However, the use of CT scan screening for early detection of lung cancer in asbestos-exposed workers requires further investigation. This study aimed to determine whether CT scan screening in asbestos-exposed workers is effective in detecting asymptomatic lung cancer using a systematic review and meta-analysis.

METHODS

We reviewed all cohort studies involving chest CT scan screening in former asbestos-exposed workers. The search strategy used the following keywords: "asbestos," "lung cancer," "screening," and "occupation*" or "work." Databases were PubMed, Cochrane Library, Science Direct, and Embase.

RESULTS

Seven studies matched our inclusion criteria. Baseline screening detected 49 asymptomatic lung cancers among 5,074 asbestos-exposed workers. Of the 49 reported lung cancers, at least 18 were in the earliest stage (stage I), accessible to complete removal surgery. The prevalence of all lung cancers detected by CT scan screening in asbestos-exposed workers was 1.1% (95% CI, 0.6%-1.8%).

CONCLUSIONS

CT scan screening in asbestos-exposed workers is effective in detecting asymptomatic lung cancer. Detection of lung cancer in asbestos-exposed workers using CT scanning is at least equal to the prevalence in heavy smokers (1%; 95% CI, 0.09%-1.1%) and also shared a similar proportion of stage I diagnoses. Screening asbestos-exposed workers could reduce mortality in proportions previously observed among heavy smokers and, thus, should not be neglected, particularly for individuals combining both exposures.

Inter-reader agreement in HRCT detection of pleural plaques and asbestosis in participants with previous occupational exposure to asbestos

OBJECTIVES

To investigate inter-reader agreement for the detection of pleural and parenchymal abnormalities using CT in a large cross-sectional study comprising information on individual cumulative exposure to asbestos.

METHODS

The project was approved by the hospital ethics committee, and all patients received information on the study and gave their written informed consent. In 5511 CT scans performed in a cohort of retired workers previously exposed to asbestos and volunteering to participate in a multiregional survey programme (Asbestos Related Diseases Cohort, ARDCO), double randomised standardised readings, triple in case of disagreement, were performed by seven trained expert radiologists specialised in thoracic imaging and blind to the initial interpretation. Inter-reader agreement was evaluated by calculating the κ-weighted coefficient between pairs of expert readers and results of routine practice and final diagnosis after expert reading.

RESULTS

κ-Weighted coefficients between trained experts ranged from 0.28 to 0.52 (fair to good), 0.59 to 0.86 (good to excellent) and 0.11 to 0.66 (poor to good) for the diagnosis of asbestosis, pleural plaques and fibrosis of the visceral pleura, respectively. κ-Weighted coefficients between results of routine practice and final diagnosis after expert reading were 0.13 (poor), 0.53 (moderate) and 0.11 (poor) for the diagnosis of asbestosis, pleural plaques and fibrosis of the visceral pleura, respectively.

CONCLUSIONS

Interpretation of benign asbestos-related thoracic abnormalities requires standardisation of the reading and trained readers, particularly for participants asking for compensation, and with a view to the longitudinal survey of asbestos-exposed workers.

Pleural plaques and the risk of pleural mesothelioma

BACKGROUND

The association between pleural plaques and pleural mesothelioma remains controversial. The present study was designed to examine the association between pleural plaques on computed tomography (CT) scan and the risk of pleural mesothelioma in a follow-up study of asbestos-exposed workers.

METHODS

Retired or unemployed workers previously occupationally exposed to asbestos were invited to participate in a screening program for asbestos-related diseases, including CT scan, organized between October 2003 and December 2005 in four regions in France. Randomized, independent, double reading of CT scans by a panel of seven chest radiologists focused on benign asbestos-related abnormalities. A 7-year follow-up study was conducted in the 5287 male subjects for whom chest CT scan was available. Annual determination of the number of subjects eligible for free medical care because of pleural mesothelioma was carried out. Diagnosis certification was obtained from the French mesothelioma panel of pathologists. Survival regression based on the Cox model was used to estimate the risk of pleural mesothelioma associated with pleural plaques, with age as the main time variable and time-varying exposure variables, namely duration of exposure, time since first exposure, and cumulative exposure index to asbestos. All statistical tests were two-sided.

RESULTS

A total of 17 incident cases of pleural mesothelioma were diagnosed. A statistically significant association was observed between mesothelioma and pleural plaques (unadjusted hazard ratio (HR) = 8.9, 95% confidence interval [CI] = 3.0 to 26.5; adjusted HR = 6.8, 95% CI = 2.2 to 21.4 after adjustment for time since first exposure and cumulative exposure index to asbestos).

CONCLUSION

The presence of pleural plaques may be an independent risk factor for pleural mesothelioma.

[Follow-up of subjects occupationally exposed to asbestos: MRI and PET scans]

MRI and PET scans are not normally used for screening and follow-up of patients following occupational exposure to asbestos. These examinations usually complement the investigation of a parenchymal mass, an effusion or pleural thickening. PET and MRI have an excellent ability to define a parenchymal lesion as malignant (cancer versus rounded atelectasis) or a pleural lesion (mesothelioma versus plaque). MRI distinguishes perfectly the involvement of sub-pleural fat by bronchial carcinoma or mesothelioma. MRI, taking account of its lack of irradiation, could be regarded as suitable for potentially repeated examinations following initial screeing by CT scan. A comparative study of multidetector scanner versus MRI, including diffusion MRI could be, nevertheless, interesting. PET cannot be proposed for the follow up or for screening on account of the irradiation induced and the difficulty of access. Pleural plaques do not take up FDG. There is no specific study of asbestos related fibrosis and there is discordance between studies of other types of pulmonary fibrosis.

[What tools should be used for follow-up post occupational exposure? What should be the frequency?]

As long as the value of screening for cancers related to asbestos is not proven in the population at risk, the medical benefits of follow-up post-professional exposure remain uncertain and the only justification is to answer the questions of anxious retired workers concerning the consequences of their past-exposure and to provide compensation for any abnormalities that are demonstrated. In this country, to answer the questions posed in the title of this contribution in the case of pathologies related to asbestos, it is necessary, after verifying the fact and the level of exposure, to identify the pleural or pulmonary fibrosis and, above all, the pleural plaques, which constitute the essential lesions currently screened for. Thoracic CT scanning without contrast is the examination of choice to achieve this objective. There are, however, two significant problems. On one hand there is a high incidence of pulmonary micronodules, the necessary surveillance of which requires subsequent scans, leading to increased irradiation and anxiety. On the other hand the diagnostic uncertainty concerning discrete lesions is a source of confusion for the persons followed-up. There are, at present, neither scientific criteria to determine the optimum frequency of examination nor any arguments for replacing the pragmatic proposals of the consensus conference of 1999. It is important, therefore, to provide a medical assessment appropriate to the symptoms and anxiety expressed by a person previously exposed to asbestos. Overall it is necessary to question the benefit to the exposed person, in terms of quality of life, of a regular search for lesions that would usually be asymptomatic if not identified. Would it not be more judicious and more equitable to compensate persons whose past-exposure is sufficient to increase significantly their risk of cancer independently of the presence of benign abnormalities.

[What are the tools for post-occupational follow-up, how should they be performed and what are their performance, limits and benefit/risk ratio? Chest X-Ray and CT scan]

Chest radiography and computed tomography (CT) are the two radiological techniques used for the follow-up of people exposed to asbestos. Since the last conference of consensus (1999), the scientific literature has primarily covered high-resolution CT and high-resolution volume CT (HR-VCT). We consider in turn the contribution of digital thoracic radiography, recommendations for the performance of HR-VCT to ensure the quality of examination while controlling the delivered radiation dose, and the need to refer to the "CT atlas of benign diseases related to asbestos exposure", published by a group of French experts in 2007, for interpretation. The results of the published studies concerning radiography or CT are then reviewed. We note the great interobserver variability in the recognition of pleural plaques and asbestosis, indicating the need for adequate training of radiologists, and the importance of defining standardized, quantified criteria for CT abnormalities. The very low agreement between thoracic and general radiologists must be taken into account. The reading of CT scans in cases of occupational exposure to asbestos should be entrusted to thoracic radiologists or to general radiologists having validated specific training. A double interpretation of CT could be considered in medicosocial requests. CT is more sensitive than chest radiography in the detection of bronchial carcinoma but generates a great number of false positive results (96 to 99%). No scientific data are available to assess the role of imaging by either CT or chest radiography in the early detection of mesothelioma.

[Chest CT: spectrum of normal findings]

A fundamental issue in the interpretation of chest CT lies in the ability to determine normality. Technical advances have resulted in an increasing number of submillimeter sections which in turn has resulted in the identification of a large number of minor abnormalities with no significant pathophysiological consequence. These images should be properly interpreted in order to avoid unnecessary follow-up examinations and radiation exposure. Often they are due to respiratory or cardiac motion artifacts. Others are explained by aging, anatomic variants, physiological phenomenon or tobacco use. These borderline imaging features detected on chest CT are described according to the main anatomical compartments of the thorax: lung and vessels, airways, pleura and chest wall, mediastinum and heart.