Orbital rule 3 : Retinoblastoma

MRI T2

MRI T1

CT image

Ultrasound image

CT image

1-It is the most common ocular lesion in childhood (within the first two years of life).
2- One third of the cases had bilateral lesions.
3-The lesion is almost always characterized by calcification.
4-CT appearance:
Hypo dense lesion seen in the globe with characteristic calcification which is pathognomonic.
-All other global lesions does not calcify. So any lesion containing calcium in childhood should be considered retinoblastoma until prove otherwise.
5-To differentiate between calcification and contrast enhancement(in case you did not do that before injection, simply look to the bone window, if it is seen, so it is a calcification and not due to contrast.
6-So to diagnose retinoblastoma, you should search for
-Calcium.
-If the lesion is running across the optic nerve and passes through optic nerve canal to reach the supra sellar area or not(extra ocular extension).
-Look at the other globe for bilaterality.
7-MRI appearances:
T1 is iso to hyper intense to vitreous.
T2 is hypo intense to vitreous.
This appearance is characteristic for retinoblastoma as all other mimic retinoblastoma lesions show hyper intensity in T1 and T2 images.
MRI enhancement is similar to that of CT.
8-If you localize a lesion occupying intra ocular space and reaching back to the extra ocular space,here you must decide the site of origin of this lesion, if it is an intra ocular one or extra ocular lesion and extending to the other space.
The answer of this question is so easy if you remember that it is commonly to see an intra ocular lesion such as retinoblastoma to extend extra ocular along the course of the optic nerve, while on the other hand, it is rarely seen that an extra ocular lesion could be seen extending intra ocular.