48 S.A. TYDSKRIF VIR LABORATORIUM- EN KLINiEKWERK 27 Junie 1964 DISCUSSION because weathered crocidolite has been used, in which the The proliferation of reticulin in the lungs of rats injected hydrocarbon content might have been extremely low. with fine asbestos particles and an asbestos-quartz admix­ However, it is doubtful whether the concentration of 3.4 ture, was found to differ significantly in the later stages of benzpyrene in virgin crocidolite would be high enough to the experiment. In the asbestos-quartz group a progressive produce neoplasms, seeing that coal dust with a relatively increase of reticulin and collagen in the dust lesions was higher concentration appeared to be inert. observed, resulting terminally in the production of com­ The present results support the conclusions of Bouser 8 pact, partially acellular, collagenous nodules. In the et af.l that silica in combination with asbestos may be asbestos group progression of the initial reticulin was extremely dangerous. limited and it ended with only slight increase in compact­ ness, with or without a few fine collagen fibres in cases SUMMARY with acute infection. The pathogenicity of pure, very fine crocidolite particles The present results demonstrate that fine asbestos par­ and of a mixture of crocidolite and quartz was investigated ticles are of a very low toxicity to lung tissue and produce after intratracheal injection of 50 mg. of these dusts into only peribronchiolar, and to a lesser degree perivascular, the lungs of rats. The proliferation of reticulin due to reticulin networks. Even in cases with acute infections, these two dusts respectively was found to differ signifi­ fibrogenesis did not progress beyond grade-2 fibrosis. The cantly. typical asbestosis of humans could not be induced with The crocidolite particles elicited an initial reticulinosis pure fine asbestos dust in the lungs of rats. However, the that became slightly more compact, with or without addition of silica dust (12,5 mg.) to the same asbestos dust collagen fibres, especially in cases with acute infections. It (37·5 mg.) led to massive fibrosis (advanced grade-3). Both appeared that exposure only to asbestos dust predisposed the maturity and the amount of fibrosis seemed excessive to acute respiratory infections. when compared to the lesions caused by equivalent The asbestos-quartz admixture gave a progressive in­ amounts of the individual dusts. The microscopic pattern crease in reticulin and collagen, resulting in partially of the pathological changes appeared to be very similar to acellular collagenous nodules (grade-3 fibrosis). The histo­ those described by Gloyne16 and Lynch and Cannon17 in logical picture of the pathological changes appeared to be humans. Bouser et af.l8 concluded that the common factor very similar to those observed in human asbestosis. in the lungs of miners of asbestos 'and iron-ore is silica Asbestos dust in combination with a small amount of free and it is suggested that this may be the carcinogenic agent, silica should be regarded as extremely dangerous. causing pulmonary fibro<;is, which precedes the initiation No malignant tumours have been produced in the of the malignant process. Do1l8 also pointed out that the experimental period by either asbestos or the asbestos­ risk of lung cancer in asbestos workers was of the order of quartz admixture. Some non-malignant pleural changes 10 times that experienced by other men. Probably this risk were observed in animals of the asbestos group with infec­ was greater before 1933 and has become progressively less tion, and in animals of the asbestos-quartz group. during recent years as the duration of employment under REFERENCES the old dusty conditions has decreased. I. Wagner, J. C. in Orenstein, A. J. ed. (1959): Proceedings of th. The fact that no malignant tumours have been produced Pneumoconiosis Conference~ Johannesburg, p. 373. London: Churchill. 2. Tobiassen, G. (1955): Acta !'lath. microbiol. scand., suppl. 105, 198. by either crocidolite asbestos or a quartz-asbestos admix­ 3. Belloni, G. and Bovo, G. (1957): Acta med. patav., 17, 367. ture might he due to the very high resistance of the rat 4. Godwin, M. C. (1957): Cancer (PhiIad.), 10, 298. 5. McCaughey, W. T. (1958): J. Path. Baet., 76, 517. species to neoplasms, as well as to the limited duration of 6. Wagner, J. C., Sleggs, C. A. and Marchand, P. (1960): Brit. J. Industr. Med., 17, 260. the present experiments. However, it appeared that free 7. Lynch, K. M. and Smith, W. A. (1935): Amer. J. Cancer, 24, 56. silica enhanced the pathogenicity of asbestos dust and 8. Doll, R. (1955): Brit. J. Industr. Med., 12, 81. 9. eartier, P. (1952): Arch. Industr. Hyg., S, 262. that in the presence of silica some pleural changes have 10. Vorwald, A. J. and Karr, J. W. (1938): Amer. J. Path., 14, 49. 11. Vorwald, A. J., Durkan, T. M. and Pratt, P. C. (1951): Arch. been produced, although not of a malignant nature. Industr. Hyg., 3, I. Recently it was pointed out by Harrington19 that oils 12. Behrens, W. (1951): Schweiz. Z. Path., 14, 275. 13. Vermaas, F. H. S. (1952): TmDS. Geol. Soc. Sth. Atr., SS, 199. containing 3.4 benzpyrene and related substances occur in 14. Gordon, H. and Sweet, H. H. (1936): Amer. J. Path., 12. 545. 15. Ross, H. F., King, E. J., Yoganathan, M. and Nagelschmidt, G crocidolite and amosite. The significance of the association (1962): Ann. Occup. Med., 5, 149. between asbestos fibres and hydrocarbons on the one hand 16. Gloyne, S. R. (1951): Lancet. I, 840. 17. Lynch, K. M. and Cannon, W. M. (1948): Dis. Chest, 14, 874. and the production of malignant neoplasms on the other 18. Bouser, G. M., Faulds, J. S. and Stewart, M. J. (955): Amer. J. Clin. Path., 25, 126. hand could not be assessed from the present experiments, 19. Harrinj?ton, J. S. (1962): Nature (Lond.), 193. 43. A CASE OF PERSISTENT THYMUS DIVERTICULA IN THE NECK J. A. KEEN, Department of Anatomy, University of Cape Town The persistence of stalks of thymic tissue in the neck, dissecting room. Descriptions of such a congenital abnor­ demonstrating the embryological origin of the thymus mality are absent in many standard anatomical and gland from the entoderm of the third- pharyngeal pouch, embryological textbooks, and only a few references could is undoubtedly a rare condition. In the course of 30 be found. In Braus' Anatomie des Menschen (1924)1 years' experience of teaching anatomy this is the first there is a schematic and hypothetical drawing of the nec': instance of such a condition that I have seen in the and upper thoracic region in the adult, with the variou i 27 June 1964 S.A. JOURNAL OF LABORATORY AND eLl ICAL MEDICINE 49 branchial outgrowths in }·l/u. The two lobes of the thymus trachea. These tructure wer pre ent on both ide, but gland are. shown to have long stalks reaching upwards that on the right was much the \ ider and thicker of the into the neck; the stalks being labelled 'cervical thymus.' two. At a later stage of the di ection, after opening the 10 Cunningham's Text-book of Anatomy (1951)2 it is thorax, these olid, cord-like band were traced to the stated that the thymus may exhibit slender prolongations remains of the thymus gland ituated in the usual anato­ into the neck on each side, antero-lateral to the trachea mical position in front of the brachiocephaLic veins stalk~ and that these prolongations are the remains of the (innominate veins) and in front of the upper part of the by which the developing thymus was connected with the pericardium (Fig. 1). third pharyngeal pouches on each side. In Patten's Human Embryology (1946)3 there is a figure showing a persistent DESCRIPTION OF THE SPECIME cord of thymic tissue on the left side of the neck, and in In the photograph of the specimen (Fig. 1) the thymus the text it is mentioned that the commonest developmental gland remains are seen as a mass of tissue no larger than irregularity involving the thymus is the persistence of is usually found in adult subjects in the dis ecting room. thymic tissue along the course followed by the gl~nd in Proceeding from this mass of tissue were two bands of its descent. Such cords may be either unilateral or bilateral. yellowish-white tissue on each side which extended up­ wards to the thoracic inlet in front of the brachiocephalic veins, and on the right side in front of the bifurcation of the brachiocephalic trunk. On the right side this band was Sup. Thyr. art. Attachment / Pharynx <;>pposite of uppermost pirif6rm fossa portion of hymus Jiverticuium to Pharynx Right inf. Isthmus Parath.glan of Thyroid Right Vagus - .."''\. Trac hea Inf. Thyr. art. Fig. 1. The dissected remains of the thymus and lle right and left thymus diverticula in the neck. T=right lobe of thyroid gland, RCCA=right common carotid artery, RThD= right thymus diverticulum, RBCV = right brachio­ cephalic vein, Tr=trachea, LThD=left thymus diverticu­ Right Thym us lum, LBCV = left brachia-cephalic vein, ThR= thymus remains. (A piece of dark cardboard has been placed be­ dive rticulum hind the mass of glandular and fatty tissue representing the remains of the thymus gland, in order to differentiate 2 it from the pericardium and the arch of aorta, in front of which it was lying.) Fig. 2. The attachment of the right thymus diverticulum to the thyroid and parathyroid glands and its upward con­ The present instance of thymic diverticula was found tinuation to the wall of the pharynx. (The common carotid by a group of student-dissectors of the 1963 anatomy artery and the vagus nerve have been displaced back­ wards.) class, Messrs.