Retinoblastoma is the Most Likely Diagnosis
In a 6-week-old infant 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
Why Retinoblastoma is the Primary Concern
Retinoblastoma accounts for approximately 50% of all leukocoria cases in infants and is the most common intraocular malignancy of childhood, with an incidence of 1/15,000-20,000 live births. 3, 4, 5
The American College of Radiology explicitly recommends that retinoblastoma be considered the most likely diagnosis in a 6-week-old infant presenting with unilateral leukocoria, and it must be excluded urgently because of its life-threatening potential. 6, 1
Normal systemic development does not rule out retinoblastoma—both retinoblastoma and congenital cataract can present with normal development while causing severe unilateral visual impairment. 2
The two most frequent presenting signs of retinoblastoma are leukocoria (71.8% of cases) and strabismus (17.9%), making leukocoria the cardinal warning sign. 4, 7, 8
Why the Other Options are Less Likely
Congenital Cataract (Option C)
- Congenital cataract is less common than retinoblastoma in infants presenting with leukocoria and carries a much lower mortality risk. 6, 3
- While congenital cataract can produce leukocoria, it is a lens abnormality rather than a retinal malignancy and can be distinguished on expert ophthalmologic examination. 3
- The absence of calcification on imaging helps differentiate cataract from retinoblastoma. 6
Toxocariasis (Option A)
- Ocular toxocariasis is extremely uncommon at 6 weeks of age and typically presents in older children (usually after age 2-3 years when environmental exposure to contaminated soil or puppies occurs). 6, 1
- Toxocariasis is a recognized cause of leukocoria but is far less likely in a neonate of this age. 3
Urgent Diagnostic Approach Required
The absence of a red reflex on examination is a critical warning sign that requires urgent ophthalmologic evaluation to rule out this life-threatening malignancy. 6, 1
Never delay ophthalmologic referral while attempting outpatient workup—leukocoria in an infant is an ophthalmologic emergency requiring evaluation within one week. 1, 2
Fundoscopic examination under dilation by a pediatric ophthalmologist establishes the diagnosis of retinoblastoma in most cases, and tissue biopsy should be avoided. 2, 3
MRI of head and orbits with and without IV contrast is the imaging modality of choice for suspected retinoblastoma, as it evaluates tumor extent, optic nerve involvement, and possible intracranial spread. 6, 3
Critical Clinical Pitfalls to Avoid
Do not assume the diagnosis is benign simply because the child is developing normally—this can be misleading and dangerous. 2
Avoid corticosteroid treatment before ophthalmologic examination, as this may worsen infectious conditions or mask accurate diagnosis. 1, 2
Approximately 15% of children with unilateral retinoblastoma have hereditary disease despite the absence of bilateral involvement or family history, so genetic testing for RB1 is recommended for all cases. 6