Tests for Retinoblastoma

Retinoblastomas are usually found when a child is brought to a doctor because they are having certain signs or symptoms.

For most types of cancer, a biopsy is needed to make the diagnosis. During a biopsy, the doctor takes a sample from the tumor and sends it to a lab to be looked at with a microscope.

But biopsies usually are not done to diagnose retinoblastoma, for 2 main reasons:

• Taking a biopsy specimen from a tumor in the eye can’t be done easily without harming the eye and risking the spread of cancer cells outside the eye.
• Retinoblastoma can usually be diagnosed accurately without a biopsy by doctors who have experience with this disease, and it’s unlikely to be confused with other eye problems in children.

Medical history and physical exam

If your child has signs or symptoms of retinoblastoma, the doctor will examine your child’s eyes and get a complete medical history to learn more about your child’s symptoms. The doctor may also ask about any family history of retinoblastoma or other cancers. This can be important when deciding if more tests and exams are needed. Your family history is also useful for determining whether other relatives could possibly pass the retinoblastoma (RB1) gene change on to their children or develop this cancer themselves (if they are young children), and if they might benefit from genetic counseling and testing.

If a retinoblastoma is suspected, the doctor will refer you to an ophthalmologist (a doctor who specializes in eye diseases), who will examine the eye closely to be more certain about the diagnosis. The ophthalmologist will use special lights and magnifying lenses to look inside the eye. Usually, the child needs to be asleep (under general anesthesia) during the exam so that the doctor can take a careful and detailed look.

If a diagnosis of retinoblastoma seems likely based on the eye exam, imaging tests will be done to help confirm it and to find out how far it might have spread within the eye and possibly to other parts of the body. Usually an ophthalmologist who specializes in treating cancers of the eye (called an ocular oncologist) will make the final determination. This doctor should also be part of the team of doctors treating the cancer.

Imaging tests

Imaging tests use x-rays, sound waves, magnetic fields, or radioactive substances to create pictures of the inside of the body. Imaging tests may be done for a number of reasons, including:

• To help tell if a tumor in the eye is likely to be a retinoblastoma
• To determine how large the tumor is and how far it has spread
• To help determine if treatment is working

Children thought to have retinoblastoma may have one or more of these tests.

Ultrasound of the eye

Ultrasound uses sound waves to create images of tissues inside the body, such as the inner parts of the eye. For this test, a small ultrasound probe is placed up against the eyelid or eyeball. The probe gives off sound waves and detects the echoes that bounce off the tissues inside and around the eye. The echoes are converted by a computer into an image on a screen.

Ultrasound is one of the most common imaging tests to confirm a child has retinoblastoma. This test can also be very useful when tumors in the eye are so large they prevent doctors from seeing inside the whole eye.

This test doesn't hurt and doesn't expose the child to radiation, but the child may need to be given medicine to help keep them calm or even asleep so the doctor can get a good look at the eye.

Optical coherence tomography (OCT) is a similar type of test that uses light waves instead of sound waves to create very detailed images of the back of the eye.

Magnetic resonance imaging (MRI) scan

An MRI scan creates detailed images using radio waves and strong magnets (instead of x-rays). MRI scans often are used for retinoblastomas because they provide very detailed images of the eye and surrounding structures, without using radiation. This test is also very good for looking at the brain and spinal cord.

Most children with retinoblastoma will have an MRI scan as part of their initial workup. For children with bilateral retinoblastomas (tumors in both eyes), many doctors continue to do MRI scans of the brain for several years after treatment to look for tumors of the pineal gland (sometimes called trilateral retinoblastoma).

Your child may have to lie inside a narrow tube for this test, which is confining and can be upsetting. This test also requires staying still for long periods of time. Young children may be given medicine to help keep them calm or even asleep during the test.

Computed tomography (CT) scan

CT scans can help determine the size of a retinoblastoma tumor and how much it has spread within the eye and to nearby areas.

Normally, either a CT or an MRI scan is needed, but usually not both. Most doctors prefer to use MRI, because CT scans use x-rays, which might raise a child’s risk for other cancers in the future. However, a CT scan can show deposits of calcium in the tumor much better than an MRI, which can be very helpful when the diagnosis of retinoblastoma is not clear.

Bone scan

A bone scan can help show if the retinoblastoma has spread to the skull or other bones. Most children with retinoblastoma don’t need to have a bone scan. It's normally used only when there is a strong reason to think retinoblastoma might have spread outside the eye.

For this test, a small amount of low-level radioactive material is injected into the blood and travels to the bones. A special camera can detect the radioactivity and creates a picture of the skeleton.

Areas of active bone changes appear as “hot spots” on the scan. These areas may suggest cancer is in an area, but other bone diseases can also cause the same pattern. To help tell these apart, other tests such as plain x-rays or MRI scans of the bone might be needed.

For more details on imaging tests, see Imaging (Radiology) Tests.

Genetic testing

When a child is diagnosed with retinoblastoma, it’s important to know if it’s the heritable (congenital) form or the non-heritable form of the disease. (See What Causes Retinoblastoma?) 

If tumors are found in both eyes (bilateral retinoblastoma), it can be assumed that the child has heritable retinoblastoma (even if there is no family history of the disease). This means they carry the mutant RB1 gene in all of their cells. Some children with retinoblastoma in only one eye might also carry the mutant RB1 gene in all of their cells. 

A blood test can be done to look for the RB1 gene change in cells outside the eye. This test can usually tell if the child has the heritable form of retinoblastoma.

Knowing which form a child has important, because children with heritable retinoblastoma have an increased risk for developing other cancers later in life, and are more likely to develop cancer if they get radiation therapy. These children will need close follow-up after treatment. (See After Treatment.) They will also have a 1 in 2 chance of passing the RB1 gene change on to each of their own children. 

A child having the heritable form of retinoblastoma can also have implications for other family members, such as brothers or sisters, who might also carry the RB1 gene change. Meeting with a genetic counselor can give you a better idea of what this risk might be and if other children in the family should be tested for the mutation. 

Sometimes tests can’t tell with certainty if a child inherited the RB1 gene change. In these cases the safest plan is to monitor the child (and other children in the family) closely for retinoblastoma with frequent eye exams.

Other tests

Other tests are not often needed for retinoblastomas, but they might be helpful in some situations.

Biopsy

For most cancers, a biopsy (removing a tissue sample from the tumor and looking at it under a microscope) is needed to make a diagnosis. But trying to biopsy a tumor at the back of the eye can often damage the eye and may spread tumor cells, so this is almost never done to diagnose retinoblastoma. Instead, doctors make the diagnosis based on eye exams and on imaging tests, like those listed above. This is why it's very important that the diagnosis of retinoblastoma is made by experts.

Lumbar puncture (spinal tap)

Retinoblastomas can sometimes grow along the optic nerve, which connects the eye to the brain. If the cancer has spread to the surface of the brain, this test can often find cancer cells in samples of cerebrospinal fluid (CSF), which is the fluid that surrounds the brain and spinal cord. Most children with retinoblastoma don’t need a lumbar puncture. It's used mainly when there is a reason to think retinoblastoma might have spread into the brain.

Typically for this test, the child is given anesthesia so they will be asleep and not move during the procedure. This can help ensure the spinal tap is done cleanly. The doctor first numbs an area in the lower part of the back over the spine. A small, hollow needle is then placed between the bones of the spine to withdraw a small amount of the fluid, which is then sent to the lab for testing.

Bone marrow aspiration and biopsy

These 2 tests might be done to see if the cancer has spread to the bone marrow, the soft, inner part of certain bones. These tests are usually not needed unless the retinoblastoma has grown outside the eye and doctors suspect it might have also spread to the bone marrow.

The tests typically are done at the same time. The samples are usually taken from the back of the pelvic (hip) bone, but sometimes they may be taken from other bones. Usually the child is given anesthesia so they will be asleep during the procedure.

For a bone marrow aspiration, a thin, hollow needle is then inserted into the bone, and a syringe is used to suck out (aspirate) a small amount of liquid bone marrow.

A bone marrow biopsy is usually done just after the aspiration. A small piece of bone and marrow is removed with a slightly larger needle that is pushed down into the bone. Once the biopsy is done, pressure is applied to the site to help stop any bleeding.

The samples are then sent to a lab to be tested for cancer cells.