Retinoblastoma

Retinoblastoma retina scan

Leukocoria in a child with retinoblastoma

Crossed eyes in a child with retinoblastoma

MRI pattern of retinoblastoma with optic nerve involvement (sagittal enhanced T1-weighted sequence)

Retinoblastoma (often abbreviated as Rb) is an uncommon eye cancer that arises from the retina, the light-sensitive inner lining of the eye. Predominantly affecting young children, it represents the leading primary malignant intraocular malignancy diagnosed in this age group. Although the prognosis for survival is generally favorable, the disease can result in vision loss or necessitate enucleation (removal of the eye).

Etiology and Genetics

Retinoblastoma's emergence can be ascribed to mutations in the chromosome 13's RB1 gene or MYCN gene aberrations. Approximately 45% of retinoblastoma cases stem from inherited genetic mutations. The RB1 gene functions as a tumor suppressor, and its dysfunction leads to unchecked cellular growth, resulting in tumorigenesis.

RB1 Gene: The hallmark of the inheritable form of retinoblastoma is the mutation in the RB1 gene situated on chromosome 13. Discovered as the inaugural tumor suppressor gene, RB1's main oncogenic restriction is achieved through the binding and inactivation of the E2F transcription factor, thereby preventing the transcription of S-phase crucial genes. Such genetic anomalies can either be passed down from parents or manifest spontaneously during early fetal development. This hereditary form predominantly results in bilateral retinoblastomas and is occasionally linked with tumors in the pineal gland or other central nervous system regions, a condition termed trilateral retinoblastoma.

MYCN Gene: A subset of non-familial, early-onset, unilateral retinoblastomas can be attributed to the MYCN oncogene's somatic amplification.

Clinical Presentation

The classical clinical sign of retinoblastoma is leukocoria (often termed "cat's eye reflex" or "amaurotic cat's eye reflex"), where the retina displays an anomalous white appearance when viewed through the pupil. Other manifestations encompass visual impairment, a reddened and irritated eye, growth delays, developmental lags, and strabismus (referred to as "cross-eyed" or "wall-eyed"). In resource-limited settings, late presentations with an enlarged eye are commonplace.

Diagnostic Evaluation

The diagnosis of retinoblastoma requires a comprehensive eye examination, usually conducted under anesthesia. While a white eye reflection (leukocoria) can suggest retinoblastoma, its presence might be due to other conditions such as Coats' disease or merely improper light reflection.

Initial screening measures for infants encompass:

• Red Reflex Test: Evaluating the retina's standard reddish-orange reflection using an ophthalmoscope in dim lighting.
• Corneal Light Reflex (Hirschberg Test): Ensures the eyes are not misaligned by observing symmetrical light reflection in both corneas.
• Eye Examination: Inspecting for any structural abnormalities.

Recent advances include smartphone applications designed to identify leukocoria in photographs.

Classification

Retinoblastomas can be categorized into heritable and non-heritable types. The heritable variant often manifests bilaterally, whereas the non-heritable form predominantly affects one eye (unilateral). However, the absence of familial history does not exclude the heritable form.

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  Drawing of a large retinoblastoma

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  Aspect of trilateral retinoblastoma on MRI

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  An ocular ultrasound of a large retinoblastoma tumor within the eye of a 3-year-old boy

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  Funduscopic finding of a retinoblastoma

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  Ocular fundus aspect of retinoblastoma

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  Gross pathology of retinoblastoma tumor in enucleated eye of 3-year-old female

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  Large exophytic white tumor with foci of calcification producing total exudative retinal detachment

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  Flexner-Wintersteiner rosettes in retinoblastoma

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  Retinoblastoma, 400 X magnification

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  Crystal structure of the retinoblastoma tumor suppressor protein bound to E2F peptide polymer

Differential Diagnosis

Radiotherapy

Retinoblastoma's clinical manifestations can mimic other ocular conditions, necessitating its differentiation from:

• Persistent Hyperplastic Primary Vitreous
• Coats Disease
• Toxocariasis
• Retinopathy of Prematurity

Treatment and Prognosis

The treatment strategy for retinoblastoma hinges on the tumor's size, number, location, and potential metastasis. Options include chemotherapy, radiation therapy, laser therapy, and surgery. The overarching goal is the eradication of the tumor, preservation of vision, and prevention of metastasis.

See Also

Eye cancer Pediatric oncology Tumor suppressor

References

Retinoblastoma Resources
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