Paediatric Pathology Online
Pathology of Retinoblastoma
Retinoblastoma, the most common intra-ocular, potentially fatal, neoplasm
of childhood is estimated to affect 1:20,000 - 34,000 live births.
It arises from the retina and most frequently presents within the first two years of life,and sometimes even at birth.
The presenting signs include a white pupil (leukocoria), squint (strabismus), poor vision, spontaneous hyphema or a red, painful eye, often with secondary glaucoma.
While most retinoblastomas are unilateral, up to 25% of the sporadic cases and most inherited retinoblastomas are bilateral.
Most retinoblastomas (about 95%) occur sporadically, but some (6 to 8%) are inherited and recent evidence suggests that the retinoblastoma (Rb) susceptibility gene, located on the long arm of chromosome 13 (13q14), is actually recessive, and not dominant as one thought.
The Rb gene, which has been sequenced, is located on chromosome 13 in close proximity to the gene for esterase D.
The oncogene N-myc is amplified 10 to 200 fold in some retinoblastomas and may play a cardinal role in the tumorigenesis of retinoblasoma.
A recent hypothesis suggests that the Rb gene normally regulates a set of proto-oncogenes, and that when both alleles of this gene are lost or inactivated, the structural transforming gene (which may be an oncogene) is expressed.
Even survivors of sporadic retinoblastoma sometimes transmit the tumour to their offspring in an apparent 'autosomal dominant' manner. These offspring are especially prone to bilateral tumours.
There is a high incidence of retinoblastoma in individuals with a deletion of chromosome 13.
Some retinoblastomas grow towards the vitreous humor and can be seen clinically with an opthalmoscope (endophytic retinoblastoma).
Others grow between the sensory retina and the retinal pigment epithelium, thereby detaching the retina (exophytic retinoblastoma).
Other retinoblastomas are both endophytic and exophytic.
The retina often contains several distinct foci of tumour in the same eye,some of which represent distinct points of origin, while others reflect tumor implantations from intravitreal dissemination.
This cream-colored tumour usually contains scattered, chalky white, calcified flecks within yellow necrotic zones.
The amount of calcification within retinoblastomas is often sufficient to be detected radiologically.
Retinoblastomas are intensely cellular and display several morphologic patterns. In some instances, densely packed, round neoplastic cells with hyperchromatic nuclei, scanty cytoplasm, and abundant mitoses are randomly distributed.
In other tumors the cells are commonly arranged radially around a central cavity (Flexner-Wintersteiner rosettes), as they differentiate towards photoreceptors.
In some retinoblastomas the cellular arrangement resembles the fleur-de-lis (fleurette).
Viable tumor cells align themselves around blood vessels, while necrotic areas with calcification are seen a short distance from the vascularized regions.
Retinoblastomas disseminate by several routes.
They commonly extend into the optic nerve, from where they spread intracranially.
They also invade blood vessels, especially in the highly vascular choroids, before metastasizing hematogenously throughout the body.
The bone marrow is a common site of blood-borne metastases, but surprisingly the lung is rarely involved.
Retinoblastomas are almost always fatal if left untreated.
However, the early diagnosis and modern therapy, survival is high (about 90%).
On rare occasions, spontaneous regression occurs for reasons that remain unknown.
Individuals with retinoblastomas have an increased susceptibility to other potentially fatal neoplasms including osteogenic sarcoma, Ewing’s sarcoma and pinealoblastoma.
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