What is the diagnosis for a 6-week-old child with leukocoria (absent red reflex) in one eye, who is otherwise developing normally?

Diagnosis: Retinoblastoma

In a 6-week-old infant presenting with unilateral leukocoria (absent red reflex), retinoblastoma must be assumed until proven otherwise and requires immediate ophthalmologic referral. 1

Why Retinoblastoma is the Primary Concern

• Retinoblastoma is responsible for approximately half of all leukocoria cases in infants, making it the most critical diagnosis to exclude due to its life-threatening nature 2
• The American College of Radiology explicitly states that retinoblastoma should be considered the most likely diagnosis in a 6-week-old infant with unilateral leukocoria 1
• Delayed diagnosis can result in permanent vision loss or death, emphasizing the urgency of this presentation 1, 3

Why Not Congenital Cataract (Option D)

While congenital cataract is the most common cause of leukocoria overall 4, several factors make retinoblastoma the priority diagnosis in this clinical scenario:

• Both conditions present identically with absent red reflex, and definitive differentiation requires specialist examination with fundoscopy and ocular ultrasound 3
• The ophthalmologist will use imaging to distinguish between these entities: absence of calcification on CT helps differentiate congenital cataract from retinoblastoma 5, 1
• The clinical approach is identical for both conditions: immediate referral to pediatric ophthalmology without delay for additional testing 1, 3

Why Not Toxocariasis (Option A)

• Ocular toxocariasis is extremely uncommon at 6 weeks of age and typically presents in older children who have had environmental exposure to Toxocara larvae 1
• Toxocariasis is listed among the differential diagnoses for leukocoria but occurs in a different age demographic than this infant 5, 2

Immediate Management Algorithm

1. Do not delay referral while attempting outpatient workup, as leukocoria in an infant is an ophthalmologic emergency 1
2. Refer immediately to pediatric ophthalmology for comprehensive evaluation including cycloplegic refraction, detailed funduscopic examination under dilation, and ocular ultrasound if media opacity blocks visualization 3, 6
3. Avoid corticosteroid treatment before ophthalmologic examination, as this may mask accurate diagnosis 1

Diagnostic Evaluation by Ophthalmologist

• Fundoscopic examination and ocular ultrasound are the primary diagnostic tools and may not require additional imaging initially 1
• MRI of head and orbits with and without IV contrast is the most useful imaging modality for evaluating malignant intraocular masses, demonstrating retrolaminar optic nerve infiltration, orbital invasion, and intracranial spread 5, 1
• CT of orbits with IV contrast may detect calcifications, which are characteristic of retinoblastoma and help differentiate it from other causes like persistent hyperplastic primary vitreous (PHPV) or Coats disease 5, 1

Critical Pitfall to Avoid

Never assume the diagnosis is benign simply because the child is developing normally. Both congenital cataract and retinoblastoma can present with normal systemic development while causing severe unilateral visual impairment or life-threatening malignancy 3. The absence of a red reflex is an absolute indication for specialist evaluation regardless of other developmental milestones 3.