What is the recommended initial imaging study to confirm a diagnosis of retinoblastoma in a child with an absent red reflex?

MRI of Head and Orbits with and without IV Contrast

For a child with absent red reflex and suspected retinoblastoma, MRI of the head and orbits with and without IV contrast is the recommended imaging study to confirm the diagnosis and complete staging. 1

Why MRI is the Correct Answer (Option C)

The American College of Radiology 2024 guidelines explicitly state that in cases of leukocoria (absent red reflex) or suspected intraocular mass in a child, MRI of the head and orbits with and without IV contrast is usually appropriate as initial imaging. 1 When a malignant intraocular or intraorbital mass like retinoblastoma is suspected, MRI of the orbits must be performed in association with MRI of the head. 1, 2

Critical Advantages of MRI Over Other Modalities

MRI provides superior soft tissue characterization that is essential for both diagnosis and staging:

• Demonstrates retrolaminar optic nerve infiltration, which determines whether tumor has extended beyond the eye—a critical factor that changes prognosis and treatment from eye-preserving to more aggressive approaches 2, 3

• Shows choroid-scleral infiltrations and orbital invasion, which upstages the disease and fundamentally alters management 2, 3

• Detects concurrent intracranial tumors in the sellar or pineal region (trilateral retinoblastoma in hereditary cases), which dramatically worsens prognosis 2, 3

• Evaluates intracranial spread of the tumor, essential for complete staging 2, 3

• Postcontrast enhancement patterns differentiate retinoblastoma from benign mimics like Coats disease, persistent hyperplastic primary vitreous (PHPV), or retinopathy of prematurity 1, 3

Why Not the Other Options?

CT (Option A) - Adjunctive Role Only

While CT can detect calcifications characteristic of retinoblastoma and help with differential diagnosis, it should not be the primary imaging modality. 3, 4 CT provides less detailed soft tissue information than MRI and exposes children to radiation—particularly problematic in a population at considerable risk of second malignancies. 4 The American College of Radiology recommends avoiding reliance on CT alone for staging. 3

Ultrasound (Option B) - Complementary but Insufficient

Ocular ultrasound complements fundoscopy and may be sufficient for initial diagnosis, but it cannot adequately assess optic nerve involvement, intracranial extension, or orbital invasion. 3, 5 Ultrasound remains economical and safe but is insufficient for complete staging required in retinoblastoma. 5

Clinical Algorithm

When a child presents with absent red reflex:

1. Urgent ophthalmologic referral for fundoscopic examination—this is an ophthalmologic emergency 3

2. Ocular ultrasound may be performed as initial complementary imaging 3, 5

3. MRI of head and orbits with and without IV contrast is the definitive imaging study for diagnosis confirmation and staging 1, 2

4. Never delay ophthalmologic evaluation while attempting outpatient workup 3

Common Pitfalls to Avoid

• Do not rely on CT alone for staging, as it provides inadequate soft tissue detail for assessing optic nerve and intracranial involvement 3

• Do not delay imaging once retinoblastoma is suspected clinically—early detection prevents progression to advanced stages 6

• Avoid radiation exposure from CT in this population already at high risk for second primary malignancies 4