What is the diagnosis for a child presenting with leukocoria (absent red reflex) in one eye, with normal development?

Retinoblastoma

In a child of any age presenting with unilateral leukocoria (absent red reflex) and normal development, retinoblastoma must be assumed until proven otherwise and requires urgent ophthalmologic evaluation within one week. 1, 2

Primary Diagnosis: Retinoblastoma (Answer B)

The American College of Radiology explicitly states that retinoblastoma should be considered the most likely diagnosis in an infant presenting with unilateral leukocoria. 1 This is a life-threatening malignancy that accounts for approximately 50% of all childhood leukocoria cases. 3

Key Clinical Features Supporting Retinoblastoma:

• Age of presentation: Mean age at diagnosis is 12 months for bilateral tumors and 24 months for unilateral tumors, making this diagnosis highly relevant even in very young infants 2
• Normal globe size: Retinoblastoma presents in a normal-sized eye, unlike PHPV or retinopathy of prematurity which are associated with microphthalmia 4, 3
• Mortality risk: If untreated, almost all patients die within two years from intracranial extension and disseminated disease 2
• Survival with treatment: 93% five-year survival rate in the United States when diagnosed and treated appropriately 2

Why Not the Other Options:

Congenital Cataract (Option C):

• While congenital cataract is the most common cause of leukocoria overall (35% of cases), it is less common than retinoblastoma in the specific context of requiring urgent exclusion of malignancy 1, 5
• The critical distinction is that retinoblastoma is life-threatening and must be ruled out first 1
• Absence of calcification on imaging helps differentiate cataract from retinoblastoma 4, 1

Toxocariasis (Option A):

• Ocular toxocariasis is extremely uncommon at 6 weeks of age and typically presents in older children 1
• Toxocaral endophthalmitis accounts for only 16% of leukocoria cases overall and represents a granulomatous reaction to the parasite 3
• This diagnosis should not be considered until retinoblastoma is excluded 1

Immediate Management Algorithm:

1. Urgent referral: Any child with leukocoria requires examination by a pediatric ophthalmologist within one week 2
2. Do not delay: Avoid attempting outpatient workup before referral, as leukocoria is an ophthalmologic emergency 1
3. Initial diagnostic tools: Fundoscopic examination and ocular ultrasound are primary diagnostic modalities 4, 1
4. Imaging when indicated: MRI of head and orbits with and without IV contrast is the most useful imaging modality for evaluating malignant intraocular masses, showing retrolaminar optic nerve infiltration, orbital invasion, and intracranial spread 4, 1
5. CT for calcification: CT of orbits with IV contrast may help detect characteristic calcifications that differentiate retinoblastoma from other causes 4, 1

Critical Pitfall to Avoid:

Never delay referral or initiate corticosteroid treatment before ophthalmologic examination, as this may worsen infectious conditions or mask accurate diagnosis. 1 The absence of a red reflex on examination is a critical warning sign requiring urgent evaluation to rule out this life-threatening malignancy. 1