A retinoblastoma is a malignant tumor of the eye. It is the most common form of eye cancer in children and is caused by a mutation on chromosome 13. A retinoblastoma is generally believed to arise from a multipotential precursor cell and exhibits three types of growth: endophytic, exophytic and diffuse infiltrating growth. The following steps will show how to diagnose a retinoblastoma.
Obtain a family history. Parents should be specifically questioned about eye tumors and other cancers in any family members. Patients with retinoblastoma have no family history 95 percent of the time.
Expect a retinoblastoma to have a large variety of presenting symptoms with a white papillary reflex the most characteristic. Squinting as a result of vision loss also is common and should prompt a fundoscopic examination through a dilated pupil. Laboratory tests may be used to eliminate other conditions similar to retinoblastomas.
Identify the retinoblastoma gene directly. DNA is taken from tumor cells or leukocytes and the gene is detected with karyotyping or Southern blotting.
Detect point mutations in the retinoblastoma gene with gel electrophoresis, direct DNA sequencing using polymerase chain reaction, ribonuclease protection or single-strand conformation polymorphism. Indirect methods may be used when the mutation can't be located. These methods detect DNA polymorphisms within the retinoblastoma gene.
Examine the suspect tumor histologically. Retinoblastomas characteristically exhibit Flexner-Wintersteiner rosettes and occasionally fleurettes. A Homer-Wright rosette is not suggestive because they are encountered in many neuroblastic tumors and few eye tumors show any glial differentiation.