**5. Diffusion weighted imaging in retinoblastoma**

Diffusion-weighted imaging (DWI) is a type of MR imaging that depends on the motion of water molecule within the tissue. Highly cellular tissue exhibits lower diffusion coefficients making this modality useful for tumor characterization. DWI is wisely wised for orbital disease as well as brain malignancy. On diffusion weighted imaging (*P* value 1000) the retinoblastoma tumor shows diffuse restriction.

A pulse sequence form of DWI that generates various imaging is referred to as ADC images (apparent diffusion coefficient) which measures the magnitude of diffusion resulting a numerical value. The mean ADC value of retinoblastoma was 0.49 ± 0.12 × 10<sup>−</sup><sup>3</sup> mm2 /s.

The low ADC values of retinoblastoma tumors are attributed to the tightly packed nature of high nuclear cytoplasmic ratio of the tumor (**Figure 11**).

The use of ADC value images has shown to be well correlated with the degree of tumor differentiation in a study conducted in Saudi Arabia. The ADC value was analyzed in different sized tumors and was shown to be significantly different with various sized tumors. It demonstrates an inverse correlation of the ADC value with the tumor size. The ADC value of small tumors (<10 mm) was 0.55 ± 0.09 × 10<sup>−</sup><sup>3</sup> mm2 /s, medium tumors (>10–15 mm) was 0.48 ± 0.09 × 10<sup>−</sup><sup>3</sup> mm2 /s, and large tumors (>15 mm) was of 0.38 ± 0.11 × 10<sup>−</sup><sup>3</sup> mm2 /s value.

In addition, the ADC value was lower in tumors with optic nerve invasion which may correlate with the tumor's likelihood to be poorly differentiated and

**Figure 11.**

*ADC (apparent diffusion coefficient) MR image of the brain and orbit showing bilateral ocular lesions with low ADC values represented tumor core representing bilateral retinoblastoma.*

aggressive [7]. *Axial diffusion weighted images: TR = 5000 ms; TE = 74 ms; number of diffusion matrix = 200 – 162; number of excitations = 1 with reconstruction of the ADC map.*

## **6. Metastasis of retinoblastoma on MRI**

Retinoblastoma tumor grows with an endophytic and/or an exophytic pattern. Endophytic growth starts from the inner layers of the retina progressing into the vitreous cavity. As the tumor cells detach from the main tumor, they can float into the vitreous and cause what is known as vitreous seeding. Detection of vitreous seeding is crucial in the staging of retinoblastoma and is considered a main prognostic indicator. Although detection of vitreous seeding by ophthalmoscopy examination is superior to MR imaging, it can be clearly identified in 63% of patient on MRI. It is usually identified as bright patches on T1 weighted imaging and dark patches on T2 weighted imaging within the vitreous cavity [5, 8] (**Figure 12**).

Exophytic growth pattern starts at the outer retinal layers and progress into the sub-retinal space causing a retinal detachment and sub-retinal tumor seeding [9].

MR imaging can detect choroidal invasion of retinoblastoma tumor at a sensitivity of 74% and a specificity of 72%. (Brisse relevance) Scleral invasion of retinoblastoma tumor can also be assessed by MR imaging with 88% sensitivity and 99% specificity [2] (**Figure 7**).

Another more aggressive pattern of retinoblastoma tumor growth is diffuse infiltrating growth pattern. In this pattern, the tumor grows along the retina as a placoid mass which subsequently results in ocular inflammation and hemorrhages. This may be seen as severe AS inflammation and a pseudohypopyon. MR images can help assess the anterior segment for the presenter absence if abnormal enhancement.

Diffuse infiltrative growth pattern is very rare (1–2%) and occurs with older age children with a male predilection of 8:1. It is usually difficult to diagnose as there are no discrete mass borders and it usually lacks the characteristic retinoblastoma calcification. A retinal detachment is commonly associated and is often evident on MRI especially on FLAIR sequence (Fluid attenuated inversion recovery) [10].

**49**

predictions.

**Figure 12.**

*CSF seeding.*

imaging were obtained.

*Uses of Radiological Imaging in Retinoblastoma DOI: http://dx.doi.org/10.5772/intechopen.86828*

**7. MRI's uses in the staging and prognosis of retinoblastoma**

Although MRI can aid in the diagnosis of retinoblastoma by the aforementioned characteristics, it is more widely used for the staging of retinoblastoma. Like all other malignancies, tumor staging in retinoblastoma is essential for the prognosis

*MRI of the spine showing areas of diffuse leptomeningeal enhancement of the spinal cord representing areas of* 

The use of MRI has changed the accuracy of assessing metastatic risk factors as the initial retinoblastoma staging of patients before the use of MRI varied after MR

The extension of retinoblastoma is usually by direct extension into adjacent structures. Intraocular extension of the tumor can easily be visualized during examination in patients with good posterior pole visualization. MR imaging has *Uses of Radiological Imaging in Retinoblastoma DOI: http://dx.doi.org/10.5772/intechopen.86828*

*Retinoblastoma - Past, Present and Future*

**6. Metastasis of retinoblastoma on MRI**

*low ADC values represented tumor core representing bilateral retinoblastoma.*

*ADC map.*

**Figure 11.**

(**Figure 12**).

enhancement.

recovery) [10].

specificity [2] (**Figure 7**).

aggressive [7]. *Axial diffusion weighted images: TR = 5000 ms; TE = 74 ms; number of diffusion matrix = 200 – 162; number of excitations = 1 with reconstruction of the* 

*ADC (apparent diffusion coefficient) MR image of the brain and orbit showing bilateral ocular lesions with* 

Retinoblastoma tumor grows with an endophytic and/or an exophytic pattern. Endophytic growth starts from the inner layers of the retina progressing into the vitreous cavity. As the tumor cells detach from the main tumor, they can float into the vitreous and cause what is known as vitreous seeding. Detection of vitreous seeding is crucial in the staging of retinoblastoma and is considered a main prognostic indicator. Although detection of vitreous seeding by ophthalmoscopy examination is superior to MR imaging, it can be clearly identified in 63% of patient on MRI. It is usually identified as bright patches on T1 weighted imaging and dark patches on T2 weighted imaging within the vitreous cavity [5, 8]

Exophytic growth pattern starts at the outer retinal layers and progress into the sub-retinal space causing a retinal detachment and sub-retinal tumor seeding [9]. MR imaging can detect choroidal invasion of retinoblastoma tumor at a sensitivity of 74% and a specificity of 72%. (Brisse relevance) Scleral invasion of retinoblastoma tumor can also be assessed by MR imaging with 88% sensitivity and 99%

Another more aggressive pattern of retinoblastoma tumor growth is diffuse infiltrating growth pattern. In this pattern, the tumor grows along the retina as a placoid mass which subsequently results in ocular inflammation and hemorrhages. This may be seen as severe AS inflammation and a pseudohypopyon. MR images can help assess the anterior segment for the presenter absence if abnormal

Diffuse infiltrative growth pattern is very rare (1–2%) and occurs with older age children with a male predilection of 8:1. It is usually difficult to diagnose as there are no discrete mass borders and it usually lacks the characteristic retinoblastoma calcification. A retinal detachment is commonly associated and is often evident on MRI especially on FLAIR sequence (Fluid attenuated inversion

**48**
