Diagnosis: Retinoblastoma
In a 6-week-old infant presenting with unilateral leukocoria (absent red reflex), retinoblastoma must be assumed until proven otherwise and requires urgent ophthalmologic evaluation. 1
Clinical Reasoning
Why Retinoblastoma is Most Likely
Retinoblastoma accounts for approximately 50% of all leukocoria cases in infants and young children, making it the single most common cause in this age group 2, 3
The American College of Radiology specifically states that retinoblastoma should be considered the most likely diagnosis in a 6-week-old infant with unilateral leukocoria 1
This is a life-threatening malignancy that requires immediate exclusion - any delay in diagnosis directly impacts both survival and the potential for vision preservation 1, 2
The absence of a red reflex on examination is a critical warning sign that mandates urgent referral to pediatric ophthalmology 1
Why NOT Congenital Cataract
While congenital cataract is the most common cause of leukocoria overall (accounting for 35-60% of cases in some series), it is significantly less common than retinoblastoma specifically in infants presenting at 6 weeks of age 4, 5
Congenital cataracts typically present bilaterally (42% bilateral vs 18% unilateral in one series), whereas this case describes unilateral involvement 5
The absence of calcification on imaging helps differentiate cataract from retinoblastoma - retinoblastoma characteristically shows calcification on CT, while cataract does not 6, 1
Why NOT Toxocariasis
Ocular toxocariasis is extremely uncommon at 6 weeks of age and typically presents in older children (usually toddlers and school-age children who have had exposure to contaminated soil or puppies) 1
Toxocariasis accounts for only 16% of leukocoria cases overall and occurs in older age groups 3
The clinical timeline makes this diagnosis highly unlikely in a 6-week-old infant 1
Immediate Management Approach
Urgent Referral Protocol
All cases of leukocoria require immediate evaluation by a pediatric ophthalmologist - this is an ophthalmologic emergency 1
Do not delay referral while attempting outpatient workup, as any delay in diagnosing retinoblastoma can be catastrophic 1
Avoid corticosteroid treatment before ophthalmologic examination, as this may mask the diagnosis 1
Initial Diagnostic Evaluation
Fundoscopic examination and ocular ultrasound performed by the ophthalmologist are the primary diagnostic tools and may establish the diagnosis without additional imaging initially 6
MRI of head and orbits with and without IV contrast is the most useful imaging modality for evaluating suspected retinoblastoma, as it demonstrates retrolaminar optic nerve infiltration, choroid-scleral involvement, orbital invasion, and potential intracranial spread 6, 1
CT of orbits with IV contrast is helpful for detecting calcifications, which are characteristic of retinoblastoma and help differentiate it from other causes like persistent hyperplastic primary vitreous (PHPV) and Coats disease 6, 7
Key Distinguishing Features on Imaging
Retinoblastoma appears as a calcified mass in a normal-sized globe, often partially necrotic, growing into the vitreous and through the choroid 3
The tumor enhances with contrast material and may appear darker than vitreous on T2-weighted MRI images 3
PHPV and retinopathy of prematurity are associated with microphthalmia (small globe), unlike retinoblastoma which occurs in normal-sized eyes 6, 3
Critical Pitfall to Avoid
The most dangerous error is assuming a benign diagnosis (like congenital cataract) without urgent ophthalmologic evaluation to definitively exclude retinoblastoma. This tumor is both vision-threatening and life-threatening, and early diagnosis is vital for optimal outcomes 2, 8. The clinical presentation of unilateral leukocoria in a 6-week-old infant mandates that retinoblastoma be the working diagnosis until proven otherwise 1.