Document 5be0E1pMQk2bB6pEeLQbv2OvR

function im%, 172). If :i)l 5 ;ignosis would generic<l for most compencriteria, there is less .posure history, or if isillcred too short to disense present, :i tis* .1 for, particularly in ich attribulabiliiy is , an open lung biopneedle biopsy (183), c changes are minid be critically exam- logic features, ..bers, and by presence of uncoatte extraction proceIso, occasionally, the in the sputum (117in tc the possibility in appropriately exthe source of ex>f course, commonly heavy and current tTTflud Afedicnl nl n with ashestosis has iderably during the : (67) and in North death, years of exears of survival aftspicuonsly in most lature death due to ems to be confined osures (McDonald, ger survival period, now surviving into id deaths from this greater importance ). In addition, it ncer is becoming a ith in the general sbestosis is restrictgiven to subjects ever the cause. The advocated, because i is known, fixed in treatment of inter- / i * ASBESTOS-RELATED LUNC DISEASES 209 current infections may be particularly impor tant in view ot the suggestion that nonspecific inflammation may contribute to progression of fibrosis (Ashcroft, 7, p. 236), There is no veal evidence to suggest that the only possible effec tive therapeutic intervention, namely, to re move die person from exposure, has any real in fluence on the outcome of the case. One assumes that removal might halt further progression, a hypothesis for which there is some evidence (62). It is also known, however, that disease can hoth appear and progress many years after removal from exposure (63); thus, research should be directed at possible ways of determining what factors determine this future progression and whether it is possible to define the stage or level of exposure at which removal might be an effec tive preventive measure. Pre-employment evaluation of lung function to screen out high-risk persons is, in theory, the most important area of future health pro tection; yet, this is also the area in which there is no systematic evidence to indicate what type of person to screen in or screen out. Attention has been directed toward the pre-employment detection of obstructive lung disease, acute or chronic, on the assumption that such per sons are at high-risk of developing asbestosis (Hunt, 5, p. 406). The smoking habit, certainly the greatest risk factor for bronchogenic cancer, does not usually constitute grounds for refus ing a recruit. Its role in the development ot fibro sis is less clear, there being some evidence to sug gest a synergistic effect with dust (185), and some evidence to the contrary. An interesting possibility, as yet completely unexplored, is that certain physiologic charac teristics, for instance, the relative sire of airways to air spaces (184), may constitute risk, factors and might, for example, be the basis for exclu sion of certain types from dust hazard. Final ly, it is possible that pre-employment and an nual measurements of lung function, particu larly FVC, might also prove to be a useful tool in the health care of the worker (87); however, this, too, should be introduced only in a way that permits a critical evaluation of the effec tiveness of suds a procedure. Malignant Mesothelioma of the Pleura and Peritoneum Primary malignant mesotheliomas arise from the pluripotential mesothelial cells (of the pleura, peritoneum, and pericardium) and in conse quence, may present with widely varying histo logic features. Nevertheless, they have been con sidered a pathologic entity (10, 185), albeit rare, for some lime; their association with asbestos exposure was mentioned as early as 1946 in an individual case report (10). This association was dramatically brought to the attention of the medical public by Wagner and colleagues (27) in a report of 33 cases with occupational and/or environmental and/or domestic exposure in the crocidolite mining area of the Northwest Cape, South Africa. The association with asbes tos exposure has now been confirmed from many parts of the world (table 6). Pathology A characteristic feature of the macroscopic appearance of the malignant variety is the ten dency to spread along serosal membranes (186), encasing the lung by a bulky, lobulated mass that usually invades the fissures. Areas of necro sis within the tumor may give rise to cystic spaces filled with glutinous fluid, a distinctive feature of this tumor, although not necessarily a specific one, because it is also seen in adenocarcinoma (10). Local metastases to chest wall, mediasti num, and pericardium, rather than remote me tastases, declare malignancy of the tumor; how ever, metastases to hilar and abdominal lymph nodes are not uncommon, and, occasionally, more distant sites, such as liver, thyroid, adre nals, bone, and biain are involved (10, 186). It has been emphasized, however, that the diag nosis is one of exclusion, and that all potential sites for primary growth (particularly lung, pan creas, intestine, and ovary) must be exam ined; consideration must also be given to the possibility that the primary tumor has already been removed (McCaughey, 5, p. 603). The peritoneal tumors present a similar appearance, but do not tend to engulf the abdominal organs to the same extent as the pleura] tumors. Gluti nous ascitic fluid, however, is a common feature (10). Primary pericardial tumors do not ap pear to be associated with asbestos exposure. Microscopically, 4 varieties are recognized ac cording to the dominant cell types (186, 187). Epithelial, or tubulopapillary, tumors are char acterized by branching.acini, lined by colum nar or cuboidai cells, often containing mucin and having a tendency to spread. Mesenchymal, or sarcomatous, tumors range in appearance from cellular fasciculated fibrosarcoma to myx oma, with the amount of associated collagen in the tumor varying considerably. The undifferen-