Retinoblastoma (Rb) is a rare form of cancer that rapidly develops from the immature cells of a retina, the light-detecting tissue of the eye. It is the most common primary malignant intraocular cancer in children, and it is almost exclusively found in young children.

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Cause:

Mutation of genes, found in chromosomes, can affect the way in which cells grow and develop within the body. Alterations in RB1 or MYCN can give rise to retinoblastoma. Almost half of children with retinoblastoma have a hereditary genetic defect associated with retinoblastoma. In other cases, it is caused by a congenital mutation in the chromosome 13 gene, 13q14.

Signs and symptoms:

Leukocoria in a child with retinoblastoma

Crossed eyes in a child with retinoblastoma

The most common and obvious sign of retinoblastoma is an abnormal appearance of the retina as viewed through the pupil, the medical term for which is leukocoria, also known as amaurotic cat’s eye reflex.

Other signs and symptoms include deterioration of vision, a red and irritated eye with glaucoma, and faltering growth or delayed development. Some children with retinoblastoma can develop a squint, commonly referred to as “cross-eyed” or “wall-eyed” (strabismus). Retinoblastoma presents with advanced disease in developing countries and eye enlargement is a common finding.

Depending on the position of the tumors, they may be visible during a simple eye exam using an ophthalmoscope to look through the pupil. A positive diagnosis is usually made only with an examination under anesthetic. A white eye reflection is not always a positive indication of retinoblastoma and can be caused by light being reflected badly or by other conditions such as Coats’ disease.

The presence of the photographic fault red eye in only one eye and not in the other may be a sign of retinoblastoma. A clearer sign is “white eye” or “cat’s eye” (leukocoria).

Diagnosis:

The red reflex: checking for a normal reddish-orange reflection from the eye’s retina with an ophthalmoscope or retinoscope from approximately 30 cm / 1 foot, usually done in a dimly lit or dark room.

The corneal light reflex / Hirschberg test: checking for symmetrical reflection of beam of light in the same spot on each eye when a light is shined into each cornea, to help determine whether the eyes are crossed.

  • Eye examination: checking for any structural abnormalities.
  • Bryan Shaw helped develop a smart-phone app that can detect leukocoria in photos.
  • If the eye examination is abnormal, further testing may include imaging studies, such as computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound. CT and MRI can help define the structure abnormalities and reveal any calcium depositions. Ultrasound can help define the height and thickness of the tumor. Bone marrow examination or lumbar puncture may also be done to determine any metastases to bones or the brain.

Differential diagnosis:

1. Persistent hyperplastic primary vitreous (PHPV): congenital developmental anomaly of the eye resulting from failure of the embryological, primary vitreous and hyaloid vasculature to regress, whereby the eye is shorter, develops a cataract, and may present with whitening of the pupil.
2. Coats disease: a typically unilateral disease characterised by abnormal development of blood vessels behind the retina, leading to blood vessel abnormalities in the retina and retinal detachment to mimic retinoblastoma.
3. Toxocara canis: an infectious disease of the eye associated with exposure to infected puppies, which causes a retinal lesion leading to retinal detachment.
4. Retinopathy of prematurity (ROP): associated with low birth weight infants who receive supplemental oxygen in the period immediately after birth, it involves damage to the retinal tissue and may lead to retinal detachment.

The various treatment modalities for retinoblastoma includes:

  • Enucleation of the eye – Most patients with unilateral disease present with advanced intraocular disease and therefore usually undergo enucleation, which results in a cure rate of 95%. In bilateral Rb, enucleation is usually reserved for eyes that have failed all known effective therapies or without useful vision.
  • External beam radiotherapy (EBR) – The most common indication for EBR is for the eye in a young child with bilateral retinoblastoma who has active or recurrent disease after completion of chemotherapy and local therapies. However, patients with hereditary disease who received EBR therapy are reported to have a 35% risk of second cancers.
  • Brachytherapy – Brachytherapy involves the placement of a radioactive implant (plaque), usually on the sclera adjacent to the base of a tumor. It used as the primary treatment or, more frequently, in patients with small tumors or in those who had failed initial therapy including previous EBR therapy.
  • Thermotherapy – Thermotherapy involves the application of heat directly to the tumor, usually in the form of infrared radiation. It is also used for small tumors
  • Laser photocoagulation – Laser photocoagulation is recommended only for small posterior tumors. An argon or diode laser or a xenon arc is used to coagulate all the blood supply to the tumor.
  • Cryotherapy – Cryotherapy induces damage to the vascular endothelium with secondary thrombosis and infarction of the tumor tissue by rapidly freezing it. Cryotherapy may be used as primary therapy for small peripheral tumors or for small recurrent tumors previously treated with other methods.
  • Systemic chemotherapy – Systemic chemotherapy has become forefront of treatment in the past decade, in the search of globe preserving measures and to avoid the adverse effects of EBR therapy. The common indications for chemotherapy for intraocular retinoblastoma include tumors that are large and that cannot be treated with local therapies alone in children with bilateral tumors. It is also used in patients with unilateral disease when the tumors are small but cannot be controlled with local therapies alone.
  • Intra-arterial chemotherapy – Chemotherapeutic drugs are administered locally via a thin catheter threaded through the groin, through the aorta and the neck, directly into the optic vessels.
  • Nano-particulate chemotherapy – To reduce the adverse effects of systemic therapy, subconjuctival (local) injection of nanoparticle carriers containing chemotherapeutic agents (carboplatin) has been developed which has shown promising results in the treatment of retinoblastoma in animal models without adverse effects.
  • Chemoreduction – A combined approach using chemotherapy to initially reduce the size of the tumor, and adjuvant focal treatments, such as transpupillary thermotherapy, to control the tumor.

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