Retinoblastoma Until Proven Otherwise
In a child presenting with unilateral leukocoria (absent red reflex) and normal development, retinoblastoma must be assumed as the diagnosis until proven otherwise, and requires urgent ophthalmologic evaluation within one week. 1, 2
Why Retinoblastoma is the Primary Diagnosis
Retinoblastoma is the most common cause of leukocoria in infants, accounting for approximately 50% of all childhood leukocoria cases, making it the most likely diagnosis that must be excluded first. 3
The American College of Radiology explicitly recommends that retinoblastoma be considered the most likely diagnosis in infants presenting with unilateral leukocoria, and this is a life-threatening malignancy that cannot be missed. 1
The mean age at diagnosis for unilateral retinoblastoma is 24 months, making this presentation at any age in early childhood highly consistent with this malignancy. 2
If untreated, almost all patients die within two years from intracranial extension and disseminated disease, which is why immediate action is critical. 2
Why Not Congenital Cataract
Congenital cataract is less common than retinoblastoma in infants presenting with leukocoria, accounting for only 35% of cases compared to retinoblastoma's dominant position. 1, 4
Congenital cataracts typically present bilaterally (though unilateral cases exist), whereas this case describes unilateral involvement, making retinoblastoma more likely. 4
The absence of calcification on imaging helps differentiate cataract from retinoblastoma—cataracts do not calcify, while retinoblastoma characteristically shows calcification on CT. 5, 1
Why Not Toxocariasis
Ocular toxocariasis is extremely uncommon at young ages (particularly at weeks of life), and typically presents in older children who have had environmental exposure to contaminated soil or puppies. 1
Toxocaral endophthalmitis accounts for only 16% of leukocoria cases and represents a granulomatous reaction to the parasite, which requires time to develop after exposure. 3
The clinical context of a very young infant with no developmental delays makes environmental parasitic exposure highly unlikely compared to a congenital or early-onset malignancy. 1
Critical Immediate Actions Required
Refer to a pediatric ophthalmologist within one week—leukocoria in an infant is an ophthalmologic emergency, and delaying referral while attempting outpatient workup is explicitly contraindicated. 1, 2
Fundoscopic examination and ocular ultrasound are the primary diagnostic tools performed by the ophthalmologist and may establish the diagnosis without additional imaging initially. 5
MRI of head and orbits with and without IV contrast is the most useful imaging modality if retinoblastoma is confirmed, as it evaluates retrolaminar optic nerve infiltration, choroid-scleral involvement, orbital invasion, and intracranial spread. 5, 1, 6
CT with IV contrast may detect characteristic calcifications that are present in retinoblastoma and help differentiate it from benign mimics like Coats disease or persistent hyperplastic primary vitreous. 5, 1
Common Pitfalls to Avoid
Never delay referral assuming this is a benign condition—the absence of a red reflex on examination is a critical warning sign requiring urgent evaluation. 1
Do not administer corticosteroids before ophthalmologic examination, as this may worsen infectious conditions or mask accurate diagnosis. 1
Avoid CT as the primary staging modality in favor of MRI to reduce radiation exposure in a population at considerable risk of second malignancies, particularly in hereditary retinoblastoma cases. 7