MRI of Head and Orbits with and without IV Contrast
For a child presenting with leukocoria (white reflex) and a retinal mass, MRI of the head and orbits with and without IV contrast is the next step for staging, as it is the most useful imaging modality for evaluating malignant intraocular masses like retinoblastoma. 1
Why MRI is Superior for Staging
MRI provides comprehensive staging information that directly impacts treatment decisions and prognosis:
MRI demonstrates retrolaminar optic nerve infiltration, which is critical for determining whether the tumor has extended beyond the eye—a key factor in staging and treatment planning 1, 2
MRI shows choroid-scleral infiltrations and orbital invasion, which upstages the disease and changes management from eye-preserving therapy to more aggressive treatment 1
MRI detects concurrent intracranial tumors in the sellar or pineal region (trilateral retinoblastoma), which occurs in hereditary cases and dramatically alters prognosis 1, 3
MRI evaluates possible intracranial spread of the tumor, which is essential for complete staging 1
Postcontrast enhancement patterns on MRI help differentiate retinoblastoma from benign mimics like Coats disease, PHPV, or retinopathy of prematurity 1
Role of CT (Limited and Complementary)
While CT has a role, it is secondary to MRI for staging purposes:
CT with IV contrast may be helpful for detecting calcifications, which are characteristic of retinoblastoma and aid in differential diagnosis 1, 4
CT can evaluate extension along optic nerves and intracranially, but provides less detailed soft tissue information than MRI 1
CT is no longer recommended as the primary imaging modality due to radiation exposure concerns, especially in children with hereditary retinoblastoma who require lifelong surveillance 3
Critical Staging Algorithm
The American College of Radiology explicitly states that when a malignant intraocular mass (retinoblastoma) is suspected, MRI of the head should be performed in association with MRI of the orbits to ensure complete staging evaluation 1
Answer: B - MRI is the correct next step for staging in this clinical scenario.