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Retinoblastoma in a porkfish (Anisotremus virginicus, Linnaeus) and a brown bullhead (Ictalurus nebulosus, Lesueur)
J. (:omp.
Path.
1989 Vol.
101
SHORT
PAPERS
Retinoblastoma
in a Porkfish (Anisotremus virginicus, Linnaeus) and a Brown Bullhead (Ictalurus ne bdosus, Lesueur ) R. Reimschuessel,
R. 0. Bennett,
E. B. May
and M. M. Lipsky
Department of Patholo
IO S. Pine Street,
Summary Two cases of retinoblastoma in fish are described. The neoplasms occurred in a porkfish (Anisotremus virginicus, Linnaeus) and in a brown bullhead (Zctalurxr nebulosus, Lesueur) .
Introduction Retinoblastoma is a neoplasm rarely seen in lower animals. The Registry of Tumors in Lower Animals (RTLA) at the National Museum of Natural History, Smithsonian Institution, Washington, D.C. contains only four such cases (RTLA 650,2030, 2747, 2901; Harshbarger, 1987). The following report describes two cases of retinoblastoma in fish which were examined at the University of Maryland Department of Pathology during 1987. The lesions occurred in a porkfish (Anisotremus uirginicus, Linnaeus) and in a brown bullhead (Ictnlurus nebulosus,Lesueur). Materials,
Methods
and Results
A porkfish weighing 720 g, with a body length 01‘310 mm, was submitted for necropsy oncluly 31st 1987. It had been on exhibit at the National Aquarium in Baltimore for at least one year. Several days before death, the fish was observed to be swimming near the surface of the tank. It was captured and placed in a smaller holding tank fol observation, but died shortly thereafter. Necropsy revealed that the right eye was proptosed and the cornea was haemorrhagic. A firm white mass, approximately 1 X 1.5 cm, containing a large blood clot was attached to the posterior aspect of the globe and occupied most of the orbit. On cut section the mass extended into the globe, fining the vitreous cavity behind the lens (Fig. 1). Fungal and bacterial cultures taken from the lesion at necropsy did not yield any organisms. The specimen was placed in Bouin’s fixative. Tissues were dehydrated, embedded in paraffin wax and sections were stained with haematoxylin and eosin (HE) (Luna, 1968). Microscopical examination of the eye revealed that the mass was composed of numerous small, undifferentiated, neuroblastic (retinoblastic) cells which had hyperchromatic nuclei and a small amount of basophilic cytoplasm. A large number of’
‘16
FL Reimschuessel
et
al.
Numerous small, poorly lbrmed. nruroepithelial mitotic figures was observed. ( Flexner-Wintersteiner) rosettes were present throughout the neoplasm I Fig. 2). ‘The retina was completely replaced by the neuroblasts. The neoplasm had surrounded the posterior third of the lens, extended through and replaced the optic nerve and infiltrated the retrobulbar connective tissue. .A large focus ofhaemorrhage was present in the choroid, extending through the mass both within the globe and in the retrobulbar area. Many necrotic foci and numerous pale eosinophilic foam) macrophages were scattered throughout the neoplasm, with several clusters of eosinophilic granulocytic cells located near the margins of the lesion. This specimen had all the characteristics of a retinoblastoma; undifferentiated neuroblasts, numerous mitotic figures, neuroepithelial rosettes and necrotic foci (Hogan and Zimmerman, 1962; Ts’o. Fine and Zimmerman, 1969). The three RTLA specimens 650, 2030 and
Retinoblastoma
in Fish
21;
L’717 had a similar histological appearance. ANo metastases were found in other organs: thrrr~ was, however, a large focus of haemorrhage in the brain. There was no evident-1% in the sections examined that this neoplasm had spread to the brain, but the intracranial haemorrhage undoubtedly led to thp animal’s death. The patholo,git.al tliagllosis was poorly differentiated retinoblastoma of the right cyc.
.\ brown bullhead measuring 207 mm was collected from the Mattawoman Creek itI Llaryland on June 2nd, 1987. Macroscopically, the left eye was small and sunken. the t‘ornca was cloudy and the pupil extremely constricted. The specimen was placed in l~ouin’s fixative and routine paraffin sections were prepared. 5licroscopit.A examination showed a mass that encompassed much of the optic nerve, extended into the globe and displaced the retina. The neoplasm had also infiltrated into the t.onnectivr tissue adjacent to the bulbar cartilage. This section of the tumour containt~tl Ions strands of retinal pigment. The neoplasm was composed mostly of a pale t.osmophilic, fibrillar, neuropil-like stroma in which neuroblastic and glial cells wcrc irregularly distributed. The neuroblastic cells had dense basophilic nuclei, with scant t‘! toplasm. Mitotic figures were rarely encountered. Occasional well-form~tl nt~uroepithelial rosettes were located withill the mass, especially in areas whrrr numerous capillaries were present (Fig. 3). A few small foci of necrosis were obser\,tad. ‘l‘he histological appearance of this specimen was very similar to the retinoblastoma dcsrribed in the spring cavefish (C’hulogastur agassi;i, Putnamj (RTLA 2901I, t)) I~ournie and Overstreet (1985). That specimen also had a fibrillar matrix in which tht Ilruroblasts were distributed. No metastasrs were seen in the other organs. ‘l‘hc, pathological diagnosis was well-differentiated retinoblastoma of the left eyr.
Discussion In children.
retinoblastoma
is the most
common
intraocular
tumour
(Hogan
and Zimmerman, 1962). Mutations or deletions in the q 14 band of chromosome 13 have been observed in numerous cases of retinoblastoma in man I Friend, Bernards, Rogelj, Weinberg, Rapaport, Albert and Dryja, 1986: Horsthemke, Greger, Barnert, Hopping and Passarge, 1987; Fung, Murphrcc, ‘I”Ang> Qan, Hinrichs and Benedict, 1987; Lee, Bookstein, Hong, Young, Shew and Lee, 1987). This locus is considered to be the site governing predisposition to hereditary retinoblastonlas. The importance ofchromosom;rl abnormalities in retinoblastomas in fish has not yet been explored. ‘l-he histogenesis of the tumour has been studied in vitro with the human I-79 retinoblastoma cell line {Chader, 1987; Kyritsis, Tsokos, Trichc alld C:hadcr, 19861. By manipulating the culture conditions, the cell lint can tx, stimulated to difrerentiate into cells exhibiting characteristics of pigmcrlt c~pithclial cells, neurons, photoreceptor cells or glia. ‘l‘hose studies indicate Ihat the rctinoblastoma may- originate from a pluripotcntial neuroectodertn;ll ~11. ‘1%~ immunorytorhemistry of tumour cc~llsin situ has demonstrated nc‘urottspet,ific cnolasc, interphotoreceptor retinoid-binding protein, S-antigen and opsxn 1Rodrigues, U’iggert, Shields. Donoso, Bardenatcin, Katz, FriendI!, al~tl Chader, 19871. This pattern of staining also indicates that the tumour ct~lls have
a neuronal
pattern
of differentiation
with
somr
photoreceptor
character-
istics. ‘The neuronal nature of the tumour was quite evident in the nroplasm tijund in the brown bullhead.
R. Reimschuessel
et al.
Fig.
3.
Photomirrograph of a section of a turnour of the eye of a brown bullhead Lesueur!. Note the fibrillar matrix surrounding the nruroepithelial rosrttcs and thr matrix along thr right and top of thr srction. HE x 300
Fig.
4.
Highrr magnification HE x500.
of a well-formed
Fl~xner~Wintrrstrinrr
roscttc
from
(kk~luru~ nrhu~o~us, the pigmrnt within
the sperimcn
iI1 Fig.
:S.
I n man, intracranial retinoblastoma can occur via subarachnoid invasion, extension of the neoplasm along the optic nerve (Rootman, Hofbauer, bY Elk
Retinoblastoma
in Fish
?I!1
stein. de Chadarevian and Little, 1984; Kopelman, Mclean and Rosenberg. 1987: Whittle, McClellan, Martin and Johnston, 1985; Stannard, Knight and Scaly, 1985). Neither of our casesshowed evidence of metastases or intracranial spread, although both neoplasms had extended into the optic nerve. Thea poorly differentiated tumour of the porkfish had extended into the retrobult);ir tissuesand contained a large area of haemorrhage. There was also a large focus of haemorrhaga in the brain of this fish, hut no tumour cells were seen in tllc, sections. The incidence of neoplasms in fish has become increasingly important as ;I possible method of monitoring carcinogens in the environment (Black, Evans, Harshbarger and Ziegel, 1982; Sinnhuber, Hendricks, Wales and Putmart. 1977; Stich and Action, 1976; Dawe and Harshbargcr, 1975; Brown, Hazdra. Keith, Greenspan, Kwapinski and Beamer, 1973; Myers, Rhodes and hicC:ain. 198’i). Because retinoblastomas are so infrequently found in fish, it is important to document their occurrence. Slides of these specimens have t~t~t~n submitted to the Registry of Tumors in Lower Animals, RTLA 3971 (1)roM.n bullhead) and RTLA 3972 (porkfish). Acknowledgments ‘rhe authors thank Dr J. Harshbarger for reviewing the slides and for providing other examples of retinoblastoma in fish for comparison. PVe would also like to thank the National Aquarium in Baltimore for the porkfish, and the Annapolis Field Office of tht United States Fish and Wildlife Service for the specimen collected from thr Mattawoman Creek. We are grateful to Christina Hauf, Pakika de Menezes Ferreira. ;\ndrew Kane and Ann Muhvich for their help and trchnical assistance. References Blac,k, ,J. J., Evans, E. D., Harshbarger, J. C. and Zeigel, R. F. i 1982). Epizootic neoplasms in fishes from a lake polluted by copper mining wastes. ~~ournal o/ the .s2ktional Cancer Institute, 69, 9 15-926. Brown, E. R., Hazdra, J. J., Keith, L., Greenspan, I., Kwapinski, J. B. G. and Beamer. P. ( 1973). Frequency of fish tumours found in a polluted watershed as compartd to nonpolluted Canadian waters. Cancer Research, 33, 189-198. Brownstein, S., de Chadarevian, J. and Little, J. M. i 1984). ‘l‘rilatrral retinohlastoma. .drchive.r of‘ U~hthaL~olo,~y, 102, 257-262. Chader, G. J. (1987). Multipotential differrntiation of human Y-79 retinohlastonla cells in attachment culture. Cell Lkfirentiation, 20, 209-216. Dawe, C. J. and Harshbarger, J. C. (1975).N eo pl asms in feral fish: their significancr to cancer research. In The Pathology oj-Fiches, W. E. Ribelin and G. Migaki, Eds. University of Wisconsin Press, Madison, N’isconsin, pp. 87 l-894. Forrrnie, J. LV. and Overstreet, R. M. ( 1985). Retinoblastoma in thr spring ca\,efisll. Chologuster aga.rsi:i Putnam. Journal of Fish Disrc~trs, 8, 377 - 38 1. Frir.nd, S. H., Bernards, R., Rogelj, S., Weinberg, R. ,4.. Rapaport, J. M., ;Ubert, 1). M. and Dryja, T. P. ( 1986). A human DNA segment with proper& of thr gcnc that predisposes to retinoblastoma and osteosarcoma. .Vature. 323, 643S646. Fuxlg, Y. K., Murphree, A. L., T’Ang, A., Q, ian,J., Hinrichs, S. H. and Benedict, i\‘. F. ( 1987). Structural evidence for the authenticit!. of the human retinohlastorna gene. .Science, 236, 1657- 166 1. Harshbarger, J. C. Personal communication with Dr ,John C. Harshbarger on November 19th, 1987. Hogan, M. J. and Zimmerman, L. E. (1962) Ophthalmic Pathology. 2nd Edit.. FY. H. Saunders Co., Philadelphia, pp. 516-525.
220
R. Reimschuessel
et nl.
Horsthemke, B., Greger, V., Barnert, H. J., Hopping, W. and Passarge, E. I 1087!. Detection of submicroscopic deletions and a DNA polymorphism at tht retinoblastoma locus. Human Genetics, 76, 257-26 1. Kopelman, J. E., Mclean, I. W. and Rosenberg, S. H. (1987). Multivariate analysis 01‘ risk factors for metastasis in retinoblastoma treated by enucleation. Ophthalmolopr. 94, 371-377. Kyritsis, A. P., Tsokos, M., Triche, T. J. and Chader, G. J. (1986). Retinoblastoma: a primitive tumour with multipotential characteristics. Invr.rti~
20, 44-54. Ts’o,
M. O., Fine, B. S. and Zimmerman, L. E. (1969). The Flexner-Wintersteiner rosettes in retinoblastoma. Archives of Pathology, 88, 664-67 1. Whittle, I. R., McClellan, K., Martin, F. J. and Johnston, I. H. (1985). Concurrent pineoblastoma and unilateral retinoblastoma: a forme fruste of trilateral retinoblastoma? *Neurosurgery, 17, 500-505. [Received for publication,
March
1 1th, 19881
Path.
1989 Vol.
101
SHORT
PAPERS
Retinoblastoma
in a Porkfish (Anisotremus virginicus, Linnaeus) and a Brown Bullhead (Ictalurus ne bdosus, Lesueur ) R. Reimschuessel,
R. 0. Bennett,
E. B. May
and M. M. Lipsky
Department of Patholo
IO S. Pine Street,
Summary Two cases of retinoblastoma in fish are described. The neoplasms occurred in a porkfish (Anisotremus virginicus, Linnaeus) and in a brown bullhead (Zctalurxr nebulosus, Lesueur) .
Introduction Retinoblastoma is a neoplasm rarely seen in lower animals. The Registry of Tumors in Lower Animals (RTLA) at the National Museum of Natural History, Smithsonian Institution, Washington, D.C. contains only four such cases (RTLA 650,2030, 2747, 2901; Harshbarger, 1987). The following report describes two cases of retinoblastoma in fish which were examined at the University of Maryland Department of Pathology during 1987. The lesions occurred in a porkfish (Anisotremus uirginicus, Linnaeus) and in a brown bullhead (Ictnlurus nebulosus,Lesueur). Materials,
Methods
and Results
A porkfish weighing 720 g, with a body length 01‘310 mm, was submitted for necropsy oncluly 31st 1987. It had been on exhibit at the National Aquarium in Baltimore for at least one year. Several days before death, the fish was observed to be swimming near the surface of the tank. It was captured and placed in a smaller holding tank fol observation, but died shortly thereafter. Necropsy revealed that the right eye was proptosed and the cornea was haemorrhagic. A firm white mass, approximately 1 X 1.5 cm, containing a large blood clot was attached to the posterior aspect of the globe and occupied most of the orbit. On cut section the mass extended into the globe, fining the vitreous cavity behind the lens (Fig. 1). Fungal and bacterial cultures taken from the lesion at necropsy did not yield any organisms. The specimen was placed in Bouin’s fixative. Tissues were dehydrated, embedded in paraffin wax and sections were stained with haematoxylin and eosin (HE) (Luna, 1968). Microscopical examination of the eye revealed that the mass was composed of numerous small, undifferentiated, neuroblastic (retinoblastic) cells which had hyperchromatic nuclei and a small amount of basophilic cytoplasm. A large number of’
‘16
FL Reimschuessel
et
al.
Numerous small, poorly lbrmed. nruroepithelial mitotic figures was observed. ( Flexner-Wintersteiner) rosettes were present throughout the neoplasm I Fig. 2). ‘The retina was completely replaced by the neuroblasts. The neoplasm had surrounded the posterior third of the lens, extended through and replaced the optic nerve and infiltrated the retrobulbar connective tissue. .A large focus ofhaemorrhage was present in the choroid, extending through the mass both within the globe and in the retrobulbar area. Many necrotic foci and numerous pale eosinophilic foam) macrophages were scattered throughout the neoplasm, with several clusters of eosinophilic granulocytic cells located near the margins of the lesion. This specimen had all the characteristics of a retinoblastoma; undifferentiated neuroblasts, numerous mitotic figures, neuroepithelial rosettes and necrotic foci (Hogan and Zimmerman, 1962; Ts’o. Fine and Zimmerman, 1969). The three RTLA specimens 650, 2030 and
Retinoblastoma
in Fish
21;
L’717 had a similar histological appearance. ANo metastases were found in other organs: thrrr~ was, however, a large focus of haemorrhage in the brain. There was no evident-1% in the sections examined that this neoplasm had spread to the brain, but the intracranial haemorrhage undoubtedly led to thp animal’s death. The patholo,git.al tliagllosis was poorly differentiated retinoblastoma of the right cyc.
.\ brown bullhead measuring 207 mm was collected from the Mattawoman Creek itI Llaryland on June 2nd, 1987. Macroscopically, the left eye was small and sunken. the t‘ornca was cloudy and the pupil extremely constricted. The specimen was placed in l~ouin’s fixative and routine paraffin sections were prepared. 5licroscopit.A examination showed a mass that encompassed much of the optic nerve, extended into the globe and displaced the retina. The neoplasm had also infiltrated into the t.onnectivr tissue adjacent to the bulbar cartilage. This section of the tumour containt~tl Ions strands of retinal pigment. The neoplasm was composed mostly of a pale t.osmophilic, fibrillar, neuropil-like stroma in which neuroblastic and glial cells wcrc irregularly distributed. The neuroblastic cells had dense basophilic nuclei, with scant t‘! toplasm. Mitotic figures were rarely encountered. Occasional well-form~tl nt~uroepithelial rosettes were located withill the mass, especially in areas whrrr numerous capillaries were present (Fig. 3). A few small foci of necrosis were obser\,tad. ‘l‘he histological appearance of this specimen was very similar to the retinoblastoma dcsrribed in the spring cavefish (C’hulogastur agassi;i, Putnamj (RTLA 2901I, t)) I~ournie and Overstreet (1985). That specimen also had a fibrillar matrix in which tht Ilruroblasts were distributed. No metastasrs were seen in the other organs. ‘l‘hc, pathological diagnosis was well-differentiated retinoblastoma of the left eyr.
Discussion In children.
retinoblastoma
is the most
common
intraocular
tumour
(Hogan
and Zimmerman, 1962). Mutations or deletions in the q 14 band of chromosome 13 have been observed in numerous cases of retinoblastoma in man I Friend, Bernards, Rogelj, Weinberg, Rapaport, Albert and Dryja, 1986: Horsthemke, Greger, Barnert, Hopping and Passarge, 1987; Fung, Murphrcc, ‘I”Ang> Qan, Hinrichs and Benedict, 1987; Lee, Bookstein, Hong, Young, Shew and Lee, 1987). This locus is considered to be the site governing predisposition to hereditary retinoblastonlas. The importance ofchromosom;rl abnormalities in retinoblastomas in fish has not yet been explored. ‘l-he histogenesis of the tumour has been studied in vitro with the human I-79 retinoblastoma cell line {Chader, 1987; Kyritsis, Tsokos, Trichc alld C:hadcr, 19861. By manipulating the culture conditions, the cell lint can tx, stimulated to difrerentiate into cells exhibiting characteristics of pigmcrlt c~pithclial cells, neurons, photoreceptor cells or glia. ‘l‘hose studies indicate Ihat the rctinoblastoma may- originate from a pluripotcntial neuroectodertn;ll ~11. ‘1%~ immunorytorhemistry of tumour cc~llsin situ has demonstrated nc‘urottspet,ific cnolasc, interphotoreceptor retinoid-binding protein, S-antigen and opsxn 1Rodrigues, U’iggert, Shields. Donoso, Bardenatcin, Katz, FriendI!, al~tl Chader, 19871. This pattern of staining also indicates that the tumour ct~lls have
a neuronal
pattern
of differentiation
with
somr
photoreceptor
character-
istics. ‘The neuronal nature of the tumour was quite evident in the nroplasm tijund in the brown bullhead.
R. Reimschuessel
et al.
Fig.
3.
Photomirrograph of a section of a turnour of the eye of a brown bullhead Lesueur!. Note the fibrillar matrix surrounding the nruroepithelial rosrttcs and thr matrix along thr right and top of thr srction. HE x 300
Fig.
4.
Highrr magnification HE x500.
of a well-formed
Fl~xner~Wintrrstrinrr
roscttc
from
(kk~luru~ nrhu~o~us, the pigmrnt within
the sperimcn
iI1 Fig.
:S.
I n man, intracranial retinoblastoma can occur via subarachnoid invasion, extension of the neoplasm along the optic nerve (Rootman, Hofbauer, bY Elk
Retinoblastoma
in Fish
?I!1
stein. de Chadarevian and Little, 1984; Kopelman, Mclean and Rosenberg. 1987: Whittle, McClellan, Martin and Johnston, 1985; Stannard, Knight and Scaly, 1985). Neither of our casesshowed evidence of metastases or intracranial spread, although both neoplasms had extended into the optic nerve. Thea poorly differentiated tumour of the porkfish had extended into the retrobult);ir tissuesand contained a large area of haemorrhage. There was also a large focus of haemorrhaga in the brain of this fish, hut no tumour cells were seen in tllc, sections. The incidence of neoplasms in fish has become increasingly important as ;I possible method of monitoring carcinogens in the environment (Black, Evans, Harshbarger and Ziegel, 1982; Sinnhuber, Hendricks, Wales and Putmart. 1977; Stich and Action, 1976; Dawe and Harshbargcr, 1975; Brown, Hazdra. Keith, Greenspan, Kwapinski and Beamer, 1973; Myers, Rhodes and hicC:ain. 198’i). Because retinoblastomas are so infrequently found in fish, it is important to document their occurrence. Slides of these specimens have t~t~t~n submitted to the Registry of Tumors in Lower Animals, RTLA 3971 (1)roM.n bullhead) and RTLA 3972 (porkfish). Acknowledgments ‘rhe authors thank Dr J. Harshbarger for reviewing the slides and for providing other examples of retinoblastoma in fish for comparison. PVe would also like to thank the National Aquarium in Baltimore for the porkfish, and the Annapolis Field Office of tht United States Fish and Wildlife Service for the specimen collected from thr Mattawoman Creek. We are grateful to Christina Hauf, Pakika de Menezes Ferreira. ;\ndrew Kane and Ann Muhvich for their help and trchnical assistance. References Blac,k, ,J. J., Evans, E. D., Harshbarger, J. C. and Zeigel, R. F. i 1982). Epizootic neoplasms in fishes from a lake polluted by copper mining wastes. ~~ournal o/ the .s2ktional Cancer Institute, 69, 9 15-926. Brown, E. R., Hazdra, J. J., Keith, L., Greenspan, I., Kwapinski, J. B. G. and Beamer. P. ( 1973). Frequency of fish tumours found in a polluted watershed as compartd to nonpolluted Canadian waters. Cancer Research, 33, 189-198. Brownstein, S., de Chadarevian, J. and Little, J. M. i 1984). ‘l‘rilatrral retinohlastoma. .drchive.r of‘ U~hthaL~olo,~y, 102, 257-262. Chader, G. J. (1987). Multipotential differrntiation of human Y-79 retinohlastonla cells in attachment culture. Cell Lkfirentiation, 20, 209-216. Dawe, C. J. and Harshbarger, J. C. (1975).N eo pl asms in feral fish: their significancr to cancer research. In The Pathology oj-Fiches, W. E. Ribelin and G. Migaki, Eds. University of Wisconsin Press, Madison, N’isconsin, pp. 87 l-894. Forrrnie, J. LV. and Overstreet, R. M. ( 1985). Retinoblastoma in thr spring ca\,efisll. Chologuster aga.rsi:i Putnam. Journal of Fish Disrc~trs, 8, 377 - 38 1. Frir.nd, S. H., Bernards, R., Rogelj, S., Weinberg, R. ,4.. Rapaport, J. M., ;Ubert, 1). M. and Dryja, T. P. ( 1986). A human DNA segment with proper& of thr gcnc that predisposes to retinoblastoma and osteosarcoma. .Vature. 323, 643S646. Fuxlg, Y. K., Murphree, A. L., T’Ang, A., Q, ian,J., Hinrichs, S. H. and Benedict, i\‘. F. ( 1987). Structural evidence for the authenticit!. of the human retinohlastorna gene. .Science, 236, 1657- 166 1. Harshbarger, J. C. Personal communication with Dr ,John C. Harshbarger on November 19th, 1987. Hogan, M. J. and Zimmerman, L. E. (1962) Ophthalmic Pathology. 2nd Edit.. FY. H. Saunders Co., Philadelphia, pp. 516-525.
220
R. Reimschuessel
et nl.
Horsthemke, B., Greger, V., Barnert, H. J., Hopping, W. and Passarge, E. I 1087!. Detection of submicroscopic deletions and a DNA polymorphism at tht retinoblastoma locus. Human Genetics, 76, 257-26 1. Kopelman, J. E., Mclean, I. W. and Rosenberg, S. H. (1987). Multivariate analysis 01‘ risk factors for metastasis in retinoblastoma treated by enucleation. Ophthalmolopr. 94, 371-377. Kyritsis, A. P., Tsokos, M., Triche, T. J. and Chader, G. J. (1986). Retinoblastoma: a primitive tumour with multipotential characteristics. Invr.rti~
20, 44-54. Ts’o,
M. O., Fine, B. S. and Zimmerman, L. E. (1969). The Flexner-Wintersteiner rosettes in retinoblastoma. Archives of Pathology, 88, 664-67 1. Whittle, I. R., McClellan, K., Martin, F. J. and Johnston, I. H. (1985). Concurrent pineoblastoma and unilateral retinoblastoma: a forme fruste of trilateral retinoblastoma? *Neurosurgery, 17, 500-505. [Received for publication,
March
1 1th, 19881