Retinoblastoma is the Most Likely Diagnosis
In a 6-week-old infant presenting with unilateral leukocoria and normal development, retinoblastoma must be assumed until proven otherwise, and this child requires urgent referral to a pediatric ophthalmologist within one week. 1, 2
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. 3
The mean age at diagnosis for unilateral retinoblastoma is 24 months, but presentation at 6 weeks, while earlier than average, does not exclude this malignancy. 2
If untreated, nearly all patients die within two years from intracranial extension and disseminated disease, making urgent evaluation imperative despite the child's normal development. 2
Normal systemic development does not rule out retinoblastoma or other serious ocular pathology—both retinoblastoma and congenital cataract can present with normal development while causing severe unilateral visual impairment. 4
Why the Other Options Are Less Likely
Congenital Cataract (Option C)
While congenital cataract is the most common cause of leukocoria overall (35% of cases), it cannot be definitively diagnosed without specialist examination including fundoscopy and ocular ultrasound to exclude retinoblastoma. 4, 5
The lens opacity in cataract blocks light transmission and prevents the red reflex, but the ophthalmologist must perform comprehensive evaluation to definitively exclude retinoblastoma before assuming a benign diagnosis. 4
Toxocariasis (Option A)
Ocular toxocariasis is extremely uncommon at 6 weeks of age and typically presents in older children, making it an unlikely diagnosis in this age group. 1
Toxocariasis accounts for only a small percentage of leukocoria cases and would be considered after excluding more common and life-threatening conditions. 3
Critical Clinical Pitfalls to Avoid
Never delay ophthalmologic referral while attempting outpatient workup—leukocoria in an infant is an ophthalmologic emergency requiring evaluation within one week. 1, 6, 2
Do not assume the diagnosis is benign simply because the child is developing normally; this can be misleading and dangerous. 4
Avoid corticosteroid treatment before ophthalmologic examination, as this may worsen infectious conditions or mask accurate diagnosis. 1, 6
Diagnostic Approach After Referral
The ophthalmologist will perform:
Fundoscopic examination under dilation, which establishes the diagnosis of retinoblastoma in most cases. 6
Ocular ultrasound (B-scan) to characterize intraocular pathology when direct visualization is blocked by media opacity, detect calcifications characteristic of retinoblastoma, and assess for retinal detachment. 4, 6
MRI of head and orbits with and without IV contrast if retinoblastoma is confirmed, as this is the gold standard for staging, demonstrating retrolaminar optic nerve infiltration, choroid-scleral involvement, orbital invasion, and intracranial spread. 7, 6
CT scanning should be avoided as initial imaging due to radiation exposure concerns, particularly problematic in retinoblastoma patients who have increased risk of second malignancies. 4, 8