DIAGNOSTIC TESTS

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DIAGNOSTIC TESTS

• Blood counts and electrolyte determination as well as urinalysis and liver function tests are useful in excluding other conditions confused with retinoblastoma

• Blood specimens should be taken not only from the patient but also from the parents and any siblings for DNA analysis, which could aid in genetic counseling

• There are direct and indirect methods in the analysis of the retinoblastoma gene

• Direct method – Aims to find the initial mutation that precipitated the

development of the tumor; then, it is determined whether that mutation is in the germline of the affected patient

• Indirect method – Used in cases where the initial mutation cannot be

located or it is uncertain whether it exists– Indirect methods of analysis of the retinoblastoma

gene rely on DNA polymorphisms within this gene

• Assays of aqueous humor enzyme levels could offer useful information to patients with suspected retinoblastoma– Lactate dehydrogenase (LDH)

• Is a glycolytic enzyme that uses glucose as an energy source• It is present in high concentrations within metabolically active

cells• Normally, its concentration in serum and aqueous humor is low

and the ratio of aqueous humor to serum LDH is less than 1.0 in patients with ocular disease other than retinoblastoma

• However, aqueous humor for eyes with retinoblastoma exhibits increased LDH activity expressed as an aqueous humor/LDH ratio of greater than 1.0

• IMAGING STUDIES– Cranial and orbital computerized tomography

provides a sensitive method for diagnosis and detecting intraocular calcification and shows intraocular extent of the tumor even in the absence of calcification

– This neuroimaging technique is also invaluable in assessing the CNS anatomy, including the optic nerve, for possible extension of retinoblastoma

• Ultrasonography – Is useful in distinguishing retinoblastomas from

non-neoplastic conditions. It is also useful in detecting calcifications

• MRI– May be beneficial in estimating the degree of

differentiation of retinoblastomas but is not as specific as computerized tomography because of its lack of sensitivity in detecting calcium

– Studies show that on T1-weighted images, the tumors usually have a low intensity and are usually difficult to distinguish from surrounding vitreous, but, on T2-weighted images, retinoblastoma tumors demonstrate very low intensity compared to vitreous.

– Calcification is more pronounced on T2 sequences– Is also useful in identifying any associated

hemorrhagic or exudative retinal detachment. This is seen as a localized subretinal area of higher signal intensity compared to vitreous on both T1- and T2-weighted sequences

• X-ray studies– In areas of the world where ultrasonography and

computerized tomography are not available, x-ray studies may be the only means of identifying intraocular calcium in patients with opaque media

• Immunohistopathologic staining– The aim of immunohistochemical studies is to decide

whether retinoblastomas come from a common progenitor cell capable of differentiation into either glial or neuronal cells or from neuron-committed cells

• Transmission electron microscopy– Ultrastructural investigations have paved the way for more

definitive descriptions of retinoblastoma. Research using this technology provided evidence of the presence of photoreceptor cell elements in retinoblastoma, and a strong evidence of retinoblastoma to human fetal retina has been demonstrated

• Patients noted to have presenting signs of retinoblastoma should undergo prompt office examination– Complete eye examination should be performed

including an estimation of the patient's visual acuity for both eyes

– A dilated fundus examination with indirect ophthalmoscopy should be completed since ancillary diagnostic studies play only a secondary role when the fundus can be visualized clearly

– A bone marrow aspiration and biopsy could be performed as well as lumbar puncture with cytocentrifuge examination for tumor cells. These may prove useful in the early diagnosis of distant spread since the primary mode of spread of retinoblastoma is hematogenous to the bone marrow and back through the optic nerve into the cerebrospinal fluid (CSF)

HISTOLOGIC FINDINGS

• The classic histologic findings of retinoblastoma are Flexner-Wintersteiner rosettes and less commonly fleurettes.

• A Homer-Wright rosette can be encountered, but they are also seen in other neuroblastic tumors.

Flexner-Wintersteiner rosette is a spoke and wheel shaped cell formation seen in retinoblastoma and certain other ophthalmic tumors. A rosette is a structure or formation resembling a rose, such as the clusters of polymorphonuclear leukocytes around a globule of lipid nuclear material, as observed in the test for disseminated lupus erythematosus.

The tumor cells that form the Flexner-Wintersteiner rosette surround a central lumen containing small cytoplasmic extensions of the encircling cells.It represents a specific form of tumor differentiation.

Reese-Ellsworth classification system

REFERENCES

• http://emedicine.medscape.com/article/1222849-diagnosis