In a child with leukocoria, which imaging study should be obtained first to confirm the diagnosis?

MRI of Head and Orbits with and without IV Contrast

In a pediatric patient presenting with white eye reflex (leukocoria), MRI of the head and orbits with and without IV contrast is the most appropriate initial imaging study to confirm the diagnosis. 1

Why MRI is the Imaging Modality of Choice

MRI is the most useful imaging modality for evaluating malignant intraocular masses, particularly retinoblastoma, which must be assumed until proven otherwise in any child with leukocoria. 1, 2

Key Diagnostic Capabilities of MRI

MRI provides comprehensive evaluation that includes: 1

• Retrolaminar optic nerve and choroid-scleral infiltrations - critical for staging retinoblastoma 1
• Orbital invasion - determines extent of disease spread 1
• Concurrent intracranial tumor in the sellar or pineal region - identifies trilateral retinoblastoma 1
• Intracranial spread of tumor - essential for treatment planning 1
• Evaluation when ocular media is unclear - when the ophthalmologist cannot visualize the optic disc 1

MRI Differentiates Causes of Leukocoria

Postcontrast enhancement patterns on MRI help differentiate retinoblastoma from other causes of leukocoria including Coats disease, persistent hyperplastic primary vitreous (PHPV), and retinopathy of prematurity. 1

Role of Other Imaging Modalities

CT Scan - Secondary Role Only

CT with IV contrast may be helpful as an adjunct for: 1

• Detecting calcifications - characteristic of retinoblastoma and helps differentiate from PHPV and Coats disease 1
• Evaluating optic nerve extension 1

However, CT should be avoided as initial imaging due to radiation exposure, which is particularly concerning in retinoblastoma patients. 3

Ultrasound - Performed by Ophthalmologist

Ocular ultrasound (B-scan) is performed by the ophthalmologist during clinical evaluation, not as a separate imaging order. 3 This is part of the comprehensive ophthalmologic examination when direct visualization of the posterior segment is blocked by media opacity. 3

Critical Clinical Algorithm

Step 1: Immediate Ophthalmology Referral

All cases of leukocoria require immediate evaluation by a pediatric ophthalmologist - referral should occur promptly without delay for imaging. 3, 2

Step 2: Ophthalmologic Examination

The ophthalmologist will perform: 3

• Fundoscopic examination under dilation
• Ocular ultrasound if media opacity prevents visualization
• Cycloplegic refraction

Step 3: Advanced Imaging

If malignant intraocular mass (retinoblastoma) is suspected, order MRI of head AND orbits with and without IV contrast together - not orbits alone. 1

Common Pitfalls to Avoid

Never delay ophthalmologic referral while ordering or waiting for imaging results - leukocoria is an ophthalmologic emergency that can result in permanent vision loss or death if treatment is postponed. 3, 2

Do not assume the diagnosis is benign simply because the child appears systemically well - both congenital cataract and retinoblastoma can present with normal systemic development while causing severe visual impairment. 3

Do not order CT as first-line imaging - the radiation exposure is particularly problematic in children with potential retinoblastoma who may require multiple imaging studies for surveillance. 3

Differential Diagnosis Context

While retinoblastoma accounts for approximately 12.5% of leukocoria cases (with congenital cataract being most common at approximately 35-80%), retinoblastoma must be excluded first due to its life-threatening nature. 2, 4, 5 MRI provides the comprehensive evaluation needed to definitively characterize the intraocular pathology and assess for features that distinguish retinoblastoma from benign causes. 1