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Histogenesis of Retinoblastoma

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Histogenesis of Retinoblastoma Editorials 131 We can now use such figures with confidence when discuss- unlikely to be followed by significant numbers suffering late ing likely outcomes ofprojected procedures with our patients decompensation. Br J Ophthalmol: first published as 10.1136/bjo.74.3.131 on 1 March 1990. Downloaded from and, hopefully, with a clear conscience. Al Faran's problems are related to factors beyond his It may therefore come as a surprise to learn how much of control. The high incidence of endemic sight-impairing our vaunted success is dependent on factors over which we disease, particularly trachoma and climatic droplet kerato- have little influence but take for granted. In Britain at least pathy (25% in this study), are gradually being overcome with our patients are still reasonably compliant. What the doctor improvements in community health. In my experience says tends to go. It does not occur to us that patients will fail droplet keratopathy is more prevalent in the poorer strata of to attend for postoperative follow-up appointments, fail to Middle Eastern society and often superimposed on pre- use the prescribed drops, or decline to be tested for or wear existing corneal scarring, due either to trachoma or smallpox. necessary spectacles. The elimination of these conditions should therefore be In this issue a paper by Dr Al Faran reports the results of followed by a similar fall in the incidence of droplet modern cataract surgery undertaken at the King Khaled Eye keratopathy. Hospital in Riyadh. The study was made because the staff at The problems concerned with the refusal of large sections the hospital considered that their results were not matching of a community to wear glasses where these are indicated are those achieved elsewhere. They report, for instance, final likely to respond only to the influence of effective universal acuities of 6/12 (20/40) or better in 37% of patients, with education, and in Saudi Arabia will take one or two genera- commensurate figures for those seeing less well. The major tions. The same applies to the reported sex differences in the responsible factor is the patients' failure to attend for patients of this study. The older age groups contain fewer refraction or to wear a spectacle correction. In many parts of females despite the higher incidence of cataract in Saudi the Islamic world and elsewhere the wearing of glasses is women. For the age groups under 50 the sexes are equally equated with blindness and can constitute a serious social represented, which hopefully indicates already some modifi- stigma. The recorded acuities above are mostly uncorrected cation of traditional social behaviour. In time, therefore, and are probably no worse than those achieved in many Al Faran or his successors will be able to serve a population Western 'centres of excellence', where, as in Riyadh, many who will not only be more prepared to report their difficulties contributing surgeons are at various stages of their surgical but also more inclined to keep their postoperative appoint- training. Imperfect techniques and inexperience are bound ments! to be associated with a higher rate ofoperative misadventure Overseas students in London have frequently complained and a wider margin for error with preoperative biometry. (to me) that sophisticated surgical techniques which have so We all have our own favourite parameters for assessing dramatically altered patients' expectations have no relevance the results of anterior segment surgical procedures. Two to the developing world. Poorer conditions called for inferior valuable ones are the postoperative incidence of retinal methods - intracapsular extraction and the Graefe knife. detachment and bullous oedema of the cornea. Al Faran Dr Al Faran has demonstrated how wrong this is. How much reports a detachment rate of 1% and no cases of persistent worse off his patients would have been had they not had the corneal oedema. Admittedly the follow-up time (mean of benefit of excellent modern management. Other surgeons of nine months only) is far too short to be dogmatic, but one sees whom we hear, working under even worse constraints, both http://bjo.bmj.com/ nothing here to suggest that the surgeons involved have cause physical and cultural, struggle to follow the precepts of their for reproof. A 6-4% rate of vitreous loss following capsular teachers and to maintain the highest possible standards. rupture is what one might expect from a surgical team They must be given every possible encouragement to including those in training, while transient postoperative persevere. oedema in as few as 4 5% has to be regarded as excellent and ARTHUR STEELE on October 3, 2021 by guest. Protected copyright. Histogenesis ofretinoblastoma More than a century ofcontroversy has surrounded the cell of embryonic neural tube differentiates into three groups of origin ofretinoblastoma. At the outset Virchow described the cells: the neuroblastic series which gives rise to neurons, the tumour as a glioma in the belief that it arose from the glial spongioblastic series which forms the glia, and the medul- cells of the retina.' Subsequently, in a report of a single case, loblastic series of cells which are primitive and undifferen- Flexner was the first to describe the rosettes which may be tiated and which may lead to either glia or neurons. Using present in retinoblastomas and to designate this tumour a gold and silver stains they classified each tumour according to neuroepithelioma.2 Later still Wintersteiner described the type of cell predominating. Several attempts were made rosettes in a series of cases and substituted the term to apply the same principles to retinoblastoma.1'0 Using neuroepithelioma for glioma, whether or not resetting was silver impregnated preparations, Mufioz-Urra identified present.3 Both authors regarded rosettes as an attempt to spongioblasts as well as astroblasts and astrocytes in the form photoreceptors, leading Verhoeff to suggest the des- histogenesis of retinoblastoma.6 cription 'retinoblastoma' in order to indicate the origin of all Parkhill and Benedict could not demonstrate any cell histological variants of the tumour from embryonic retinal processes or fibrils indicative either ofglia or ofneurons using cells and to parallel the name 'neuroblastoma.' special stains and regarded the cells they saw as primitive and The term retinoblastoma was adopted by the American undifferentiated.7 They postulated that the tumour was Ophthalmological Society in 1926.' In the same year Bailey derived by dedifferentiation of normal astrocytes or Muller and Cushing produced a classification ofbrain tumours based cells rather than from primitive precursors. They argued that on histogenesis.I The medullary epithelium lining the the rosettes in retinoblastoma represented an attempt to 132 Hungerford 1 Virchow R. Die Krankhaften Geschwulste. Berlin: Hirschwald, 1864; 2:151. reproduce the primitive epithelium of ependymal cells in the 2 Flexner S. A peculiar glioma (neuroepithelioma?) of the retina. Bulljohns Hopk neural tube. Similar rosettes are seen in ependy- Hosp 1891;2: 115-9. embryonic Br J Ophthalmol: first published as 10.1136/bjo.74.3.131 on 1 March 1990. Downloaded from 3 Wintersteiner H. Das Neuroepithelioma retinae: eine anatomische und klinische momas. Because of this, and in accord with the wide Studie. Leipzig: Deuticke, 1897. acceptance of the term glioma for all brain tumours of 4 VerhoeffFH, Jackson E. Minutes of the proceedings of the sixty-second annual meeting. Trans Am Ophthalmol Soc 1926; 24: 38-43. neuroectodermal origin, they chose to revert to the glioma 5 Bailey P, Cushing H. A classification of tumors of the glioma group on a histologic description for the retinal tumour, subclassifying the neo- basis with a correlated study ofprognosis. Philadelphia: Lippincott, 1926. 6 Munoz-Urra F. Ueber die feine Gewebsstruktur des Glioms der Netzhaut. plasms as of retinoblastoma type when the cells were Graefes Arch ClinExp Ophthalmol 1923; 112: 133-51. undifferentiated like those of neuroblastomas or medul- 7 Parkhill EM, Benedict WL. Gliomas of the retina: a histopathologic study. Am ] Ophthalmol 1941;24: 1354-73. loblastomas, of neuroepithelioma type when partial dif- 8 Grinker RR. Gliomas of the retina; including the results of studies with silver ferentiation was indicated by rosette formation like that of impregnations. Arch Ophthalmol 1931; 5: 920-35. 9 Favaloro G. Sui glioblasto-spongioblastomi anaplastici e differenziati della primitive spongioblastic cells, and of astrocytoma type in the retina. Ann Ottalmol Clin Oculist 1937; 65: 881-918. rare examples when the tumour cells were nearly as well 10 Sussman W. Intraocular tumours. Br] Ophthalmol 1938; 22: 722-37. 11 Broders AC. Cancer's selfcontrol. Med] Rec 1925; 121: 133-5. differentiated as normal astrocytes. 12 Broders AC. Practical points on the microscopic grading of carcinoma. NY On similar principles, Broders graded retinoblastomas StatejMed 1932; 32: 667-71. 13 Broders AC. The grading of cancer: its relationship to metastasis and prognosis. from I for true gliomas composed of more or less mature Texas]Med 1933; 29: 520-5. astrocytes to IV for the majority of retinoblastomas with no 14 Tso MOM, Zimmerman LE, Fine BS. The nature of retinoblastoma: I. Photoreceptor differentiation: a clinical and histologic study. Am J Oph- cellular differentiation." ". Grinker was in agreement with thalmol 1970; 69: 339-49. his predecessors that the presence of rosettes was indicative 15 Tso MOM, Fine BS, Zimmerman LE. The nature of retinoblastoma: II. Photoreceptor differentiation: an electron microscopic study. Am ] Oph- of an origin from primitive rods and cones, and he retained thalmol 1970; 69: 350-9. the term neuroepithelioma for tumours with this feature. 16 Sang DN, Albert DM. Catecholamine levels in retinoblastoma. In: Jakobiec, FA ed. Ocular and adnexal tumors. Birmingham: Aesculapius, 1978. However, he considered that tumours without rosettes arose 17 Squire J, Goddard AD, Canton M, Phillips RA, Gallie BL. Tumour induction from primitive retinal epithelial cells capable either of by the retinoblastoma mutation is independent of N-mvc expression.
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