A retinoblastoma is a rare malignant tumor of the retina. It occurs as both hereditary and non-hereditary forms. It is seen typically in children who are below the age of 5 years.

The diagnosis of retinoblastoma is a clinical diagnosis. The most characteristic symptom is a whitish reflex from the pupils of the affected eye in children. This is most often picked up when a flash photo is taken, and the pupils look white instead of the normal orange-red glow. This sign is called leukocoria or cat’s eye pupil. Other symptoms include strabismus, or crossed eyes. This may be discovered by the parents, and may be confirmed by uncovering each eye in turn while the child is looking at some object.

Some children complain of redness and soreness of the eyes. This pseudoinflammation is seen in about a tenth of such patients. Other less common symptoms include bulging of the eyeball, discoloration of the iris in the eye with the tumor, differences in the size, shape and activity of the pupil of the affected eye, and symptoms due to metastasis such as bone pain. Visual acuity may be affected, or the child may complain of double vision.

Confirmation of Diagnosis

An indirect ophthalmoscopy is required to confirm the diagnosis of retinoblastoma. This is done through dilated pupils, and examination under anesthesia is required in very young children and infants. The interior of the eyeball must be thoroughly visualized, including the whole of the retina and the optic nerve head. A slit lamp examination, called biomicroscopy, is also done to examine the inside of the eye using a powerful focused light beam and a microscope.

Further eye tests may be ordered:

• Fluorescein angiography: a dye called fluorescein is injected into the blood vessels of the eye to look for blocked or dilated or leaking vessels on an X-ray film.
• Ultrasonography of the eyeball: ultrasound waves are used to create a picture of intraocular tissues.
• Magnetic resonance imaging (MRI): this gives a more detailed image of soft tissues, including the spread of the tumor into nearby tissues.
• Computerized tomography (CT) scanning: this uses a series of X-rays taken from different angles to synthesize a composite image of the area images. It is often avoided in young children, especially if they have a family history of retinoblastoma or other tumors, because of the potential danger of exposure to ionizing radiation.

A full physical examination of the child is done as usual to pick up signs of related or unrelated disease. A bone scan may be required to check for signs of bone spread.

Treatment of a Retinoblastoma

How a retinoblastoma is treated depends upon:

• Tumor size
• Tumor number
• Tumor location
• Extent of involvement of intraocular and extraocular structures
• Any other tumor
• Family history of retinoblastoma
• Extent to which vision can be conserved

In any case, the treatment of a retinoblastoma requires the services of a team of health care providers who have experience with childhood cancer treatment. The aims of treatment are to prevent death from cancer, as well as to save the child’s eye, and vision if possible, as well as achieving the minimum possible side effects.

Treatment Approaches

• Cryotherapy: a cryoprobe is used to freeze and destroy tumors with a diameter of up to 5mm and thickness of 3mm. This technique may need to be repeated, with intervals of 3-4 weeks.
• Laser photocoagulation: laser light energy is used to heat tumors and destroy their blood supply, making them non-viable, or in other cases to render them more sensitive to other tumor-ablating techniques.
• Thermotherapy: microwaves are used to heat the tumor cells and destroy them.
• Radiotherapy: both external beam irradiation and brachytherapy are used. External beam radiation therapy has the advantage of greater precision, sparing surrounding tissues and therefore conserving more vision. Three modalities are in use: intensity modulated radiation therapy (IMRT), stereotactic external beam radiation therapy (gamma knife), and proton beam radiation therapy.

Brachytherapy consists of plaque radiotherapy, where radioactive metals like I-125, are placed in the form of seeds on a plaque, which is sutured to the sclera outside the tumor. The plaque remains in position from 3 to 7 days depending on tumor size and extent. Radiation therapy is associated with a greater risk of side effects to the brain and the eye, in the very young children who are the typical targets of this cancer.

• Chemotherapy: systemic chemotherapy is used when distant metastases have occurred. Drugs used include cisplatin, etoposide and vincristine. A specialized form of chemotherapy involves the use of high dosages of very potent drugs, with the use of stem cells to replenish the stock of non-tumorous cells such as bone marrow cells which are also severely affected by the chemotherapy regimen – called stem cell rescue. Chemotherapy may be administered intravenously, orally, or intra-arterially (into the artery that supplies the eyeball – only for tumors limited to the eye), or intrathecally (into the space around the central nervous system containing cerebrospinal fluid).
• Enucleation: this surgical procedure involves the removal of the entire eye, with part of the optic nerve. It is often used with larger or more extensive tumors. It may also be the second-line therapy if radiation or other eye-sparing techniques fail, and if there is no hope that vision can be conserved. It is usually combined with the insertion of an adult-size artificial eye implant to which the ocular muscles are reattached. This helps eye movements to look more natural. In addition, a skillfully colored shell is fitted over the implant to simulate the appearance of the normal eye. The child must be followed up for recurrence or a new tumor for at least 2 years.
• Orbital exenteration: this procedure involves the removal of all intraorbital tissue, and is a disfiguring surgery.

Late effects of treatment include:

• Effects of radiation on the growth of the face may produce midfacial hypoplasia, as well as problems with hearing and vision
• Effects on cognition and mood
• Second cancers especially of the lung or bladder, osteosarcomas or sarcomas, or melanomas, are quite common in individuals with a heritable form of retinoblastoma

About nine of every ten children with retinoblastoma are cured, or show no recurrence of the tumor in five years after treatment. Life-long follow up is mandatory because of the high risk of second tumors, and tumor development in the other eye. This is usually seen to happen within the first 3 years after the first tumor develops, so the eyes should be examined every 2-4 months for at least 28 months. The risk of trilateral retinoblastoma is high with the heritable form. For this reason, MRI scanning is required every six months, until the child is at least five years old.

Source: News Medical

February 2024