Retinoblastoma is the Most Likely Diagnosis
In a young infant presenting with unilateral leukocoria (absent red reflex) and otherwise normal development, retinoblastoma must be assumed until proven otherwise and requires urgent ophthalmologic referral within one week. 1, 2
Why Retinoblastoma is the Primary Concern
The clinical presentation strongly suggests retinoblastoma based on several key factors:
- Retinoblastoma accounts for approximately 50% of all childhood leukocoria cases, making it the single most common cause of this finding 3, 4
- The mean age at diagnosis for unilateral retinoblastoma is 24 months, but it commonly presents in infancy, making this age-appropriate for the diagnosis 2
- This is a life-threatening malignancy where untreated patients have nearly 100% mortality within two years from intracranial extension and disseminated disease 2
- Normal systemic development does not exclude retinoblastoma, as the tumor affects only the eye initially while the child continues to develop normally 5
Why the Other Options Are Less Likely
Congenital Cataract (Option C)
- While congenital cataract can cause leukocoria by blocking light transmission through the lens, it is less common than retinoblastoma in infants presenting with this finding 1
- Cataract would show absence of calcification on imaging, which helps differentiate it from retinoblastoma 6
- The ophthalmologist can definitively distinguish between these conditions through fundoscopic examination and ocular ultrasound 1, 5
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 the parasite 1
- Toxocariasis accounts for only 16% of leukocoria cases overall and manifests as a granulomatous reaction in the vitreous 3
- The age of presentation makes this diagnosis highly unlikely in this clinical scenario 1
Critical Next Steps
Immediate referral to a pediatric ophthalmologist is mandatory - this is an ophthalmologic emergency that should not be delayed for outpatient workup or additional testing 1, 5, 2
The ophthalmologist will perform:
- Fundoscopic examination under dilation, which establishes the diagnosis in most cases 7
- Ocular ultrasound (B-scan) to characterize the intraocular mass, detect calcifications, and assess for retinal detachment 5, 7
- MRI of head and orbits with and without IV contrast if retinoblastoma is confirmed, as this is the gold standard for staging and evaluating optic nerve invasion, orbital extension, and intracranial spread 6, 7
Common Pitfall to Avoid
Never assume the diagnosis is benign simply because the child is developing normally - both retinoblastoma and congenital cataract can present with normal systemic development while causing severe unilateral visual impairment 5. The absence of systemic symptoms does not reduce the urgency of evaluation, as retinoblastoma has a 93% five-year survival rate when diagnosed and treated promptly 2.