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 requiring immediate exclusion because it is a life-threatening malignancy that, if untreated, results in death from intracranial extension within two years. 2
The American College of Radiology explicitly recommends that retinoblastoma be considered the most likely diagnosis in infants presenting with unilateral leukocoria. 1
Leukocoria in an infant is an ophthalmologic emergency and referral should not be delayed while attempting outpatient workup. 1
The mean age at diagnosis for unilateral retinoblastoma is 24 months, making this presentation at any age in early childhood highly suspicious. 2
Why Not the Other Options
Congenital Cataract (Option C)
While congenital cataract can cause leukocoria, it is less common than retinoblastoma in infants presenting with this finding. 1
Congenital cataract accounts for 35% of leukocoria cases overall, but the critical distinction is that retinoblastoma must be excluded first due to its life-threatening nature. 3
Imaging characteristics help differentiate: congenital cataract shows absence of calcification, whereas retinoblastoma typically demonstrates calcification on CT. 4, 1
Toxocariasis (Option A)
Ocular toxocariasis is extremely uncommon at this young age and typically presents in older children who have had environmental exposure to Toxocara parasites. 1
Toxocaral endophthalmitis accounts for only 16% of leukocoria cases and appears as a granulomatous reaction in the vitreous without the calcification characteristic of retinoblastoma. 5
The clinical context of normal development and young age makes toxocariasis highly unlikely. 1
Immediate Diagnostic Approach
All cases of leukocoria require immediate evaluation by a pediatric ophthalmologist, with examination occurring within one week of detection. 1, 2
Primary diagnostic tools include fundoscopic examination and ocular ultrasound performed by the ophthalmologist. 4, 1
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 intracranial spread. 4, 6
CT with IV contrast may be helpful for detecting characteristic calcifications that differentiate retinoblastoma from benign mimics. 4, 1
Critical Pitfall to Avoid
Do not delay ophthalmologic referral to obtain imaging first—the clinical examination by a pediatric ophthalmologist is the priority, and they will determine appropriate imaging based on their findings. 1, 2