**3. Computerized tomography imaging in retinoblastoma**

Computerized tomography (CT) is a combination of multiple X-ray images from different angles producing cross sectional images. Like standard X-ray, CT depends on relative the radio-density of different tissue structures. CT delivers ionization radiation reaching to 1–10 mSv per brain CT. Retinoblastoma appears as a hyperdense lesion on CT in relation to the surrounding hypodense ocular vitreous (**Figure 3**).

CT scan is also another beneficial tool in detecting calcification which may be seen in a non-homogenous pattern in most large tumors (**Figure 4**) or in a homogenous pattern in smaller tumors. In certain studies, CT scan has failed to show calcification in small retinoblastoma tumors [2–4] CT images can also be useful to detect any associated metastatic brain lesions (**Figure 5**).

CT scan is not the modality of choice for diagnosis and follow-up of children with retinoblastoma due to radiation exposure (ionizing radiation) and the high sensitivity of MRI for soft tissue. This reduces the implantation of CT in retinoblastoma cases especially in areas where MR studies are accessible [3].

#### **Figure 3.**

*CT (soft tissue window image) showing right globe hyperdense vitreous, retrolental intraocular solid mass with dystrophic calcification and proximal calcified optic nerve local invasion.*

#### **Figure 4.**

*CT (bone window image) showing right globe enlargement, hyperdense vitreous due to hemorrhage, retrolental intraocular solid mass with central large dystrophic calcification and an enlarged proximal calcified optic nerve due to local invasion.*

#### **Figure 5.**

*A non-contrast brain CT for follow up of retinoblastoma patient, showed solid suprasellar mass with faint calcification suggestive of metastasis.*
