Retinoblastoma (RB) is a malignant tumor of the developing retina that occurs in children, usually before age 5 years, and may be unilateral or bilateral. See the image below. About 60% of patients have unilateral RB, with a mean age at diagnosis of 24 months, and about 40% have bilateral RB, with a mean age at diagnosis of 15 months.
Mutations in the RB gene (chromosomal location 13q14) predispose individuals to the disease, as well as to an increased risk of developing pineal tumors, extracranial sarcomas, and melanoma. When a patient with RB develops a pineal tumor, the term trilateral RB (TRB) is used. [1, 2, 3]
RB may occur sporadically (60%), or it may be inherited (40%). Historically, the RB trait seemed to be transmitted in an autosomal dominant pattern. Occasionally, however, the trait skips a generation in families, indicating genetic carriers.
The volume of the intraocular tumor is estimated by means of orbital A and B scanning and/or a computed tomography (CT) scanning. On rare occasions, RB is discovered during a well-baby examination. Most often, a parent first detects the symptoms of RB. See the image below.
de Jong et al reviewed the literature on the accuracy of MRI and CT in determining the extent of the tumor in advanced retinoblastoma. They concluded the MRI images showed higher diagnostic accuracy for detecting prelaminar optic nerve and choroidal invasion, but the differences were not statistically significant. Although MRI techniques still need to be improved, the assessment of CTs showed low accuracy. 
On CT scans, RB is seen as a mass that is predominantly located in the posterior ocular pole. The mass may have distinct contours and an inhomogeneous structure, and it may contain calcifications in 70.5% of cases.
CT scanning has high sensitivity in the detection of intraocular tumors, and it has a specificity of 91% for RB. This modality has allowed the staging of intraocular tumors, the detection of extrabulbar growth, and the determination of further treatment approaches. CT scanning can be used to follow up tumors to determine the effect of treatment and to establish a timely diagnosis of malignant tumor relapses.
An epibulbar osseous choristoma can simulate extraocular extension of RB in an eye with an intraocular malignancy; however, the intraocular contents display features typical of RB without extraocular extension.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is not as specific for diagnosing RB as CT scanning because of MRI's insensitivity for detecting calcium. When calcium is detected, it may be seen as an area of low signal intensity on all pulse sequences. 
RB is usually visualized as a mass that is slightly hyperintense relative to the vitreous on T1-weighted images and that is hypointense on T2-weighted images. T1 hyperintensity may be due to the presence of melanin. Mild to marked enhancement is seen on gadolinium–enhanced T1-weighted images.
One study compared diagnostic gadolinium-enhanced T1-weighted MRI image quality without and with fat saturation. Thirty-six children (mean age, 19.0 ± 16.8 [SD] months) were included. Image quality and anatomic detail depiction were found to be significantly better without fat saturation, but tumor enhancement was rated higher with fat saturation. Detection of choroidal invasion was improved without fat saturation, but fat saturation improved detection of (post-)laminar optic nerve infiltration. According to the authors, combining both sequences was the best approach in assessing tumor extension (sensitivity and specificity for (post-)laminar optic nerve infiltration were 75% and 100%, respectively; sensitivity and specificity for choroidal invasion were 87.5% and 85.7%, respectively). 
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the topic Nephrogenic Systemic Fibrosis.
Like CT scanning, MRI has a role in the detection of extraocular tumor spread, especially extension into the optic canal. It can also depict intracranial tumors associated with TRB.
Retinal detachment is well depicted on MRI.
Three-dimensional (3D) ultrasonography can be used to perform retinal and tumor mapping, which is useful in planning localized or plaque radiation. Subsequently, 3D ultrasonography can also help confirm the proper positioning of such plaques. In addition, calcification and retinal detachment can be diagnosed with this modality; however, 3D ultrasonography is not useful for depicting the extraocular spread of tumors. General anesthesia must be a part of this examination, because the eye should be still during the scan. [7, 8]
Color Doppler imaging reveals slightly vascularized tumor areas and can depict blood flow inside the tumor.
Retinal fluorescein angiography helps to confirm the diagnosis of RB. However, it is not usually performed for this disease because of the availability of noninvasive, cross-sectional imaging methods. 
False-positive results can occur in cases involving other, similar pathologies.