Retinoblastoma
The most likely diagnosis is retinoblastoma (Option C), as the presence of retinal calcifications in a child with leukocoria is pathognomonic for this malignancy. 1
Diagnostic Reasoning
The American College of Radiology explicitly states that calcifications within well-demarcated retinal lesions in a child with leukocoria are pathognomonic for retinoblastoma, distinguishing it from other causes of leukocoria. 1 This is the critical diagnostic feature in this case.
Why Not Coats Disease (Option B)?
- Coats disease does NOT present with calcifications. The American College of Radiology explicitly states that the absence of calcification on imaging is what differentiates Coats disease from retinoblastoma, meaning calcifications would not be present in Coats disease. 1
- While Coats disease is a common mimic of retinoblastoma and presents with leukocoria, the presence of calcifications on fundoscopy rules it out. 2, 3
- Coats disease is among the most common pseudoretinoblastoma diagnoses across all age groups, but it lacks the calcified retinal lesions seen here. 3
Why Not Toxoplasmosis (Option A)?
- Congenital toxoplasmosis (likely what "toxicosis" refers to) is not listed among the common causes of leukocoria in children by the American College of Radiology guidelines, which include retinoblastoma, persistent hyperplastic primary vitreous (PHPV), retinopathy of prematurity, Coats disease, congenital cataract, and larval granulomatosis. 1
- Toxoplasmosis typically presents with chorioretinal scars rather than the calcified retinal masses characteristic of retinoblastoma.
Critical Clinical Context
Age and Presentation
- This 1-year-old infant fits the typical presentation age for retinoblastoma. Bilateral retinoblastoma typically presents at 18-24 months, while unilateral disease presents around 36 months, though cases can occur earlier. 4
- Leukocoria is one of the two most frequent presenting symptoms of retinoblastoma (along with strabismus). 5, 6, 7
Family History Considerations
- The absence of family history does NOT exclude retinoblastoma. Family history may be absent in hereditary cases due to de novo germline RB1 pathogenic variants or variants with reduced penetrance. 4
- Sixty percent of retinoblastomas are unilateral and most are not hereditary, presenting at a median age of 2 years. 5, 7
- All bilateral and multifocal unilateral forms are hereditary, but unilateral cases can still be hereditary in some instances. 5, 7
Immediate Management Imperatives
- Retinoblastoma must be assumed until proven otherwise in any child presenting with leukocoria. 1
- Never delay ophthalmologic referral—leukocoria in a child is an ophthalmologic emergency requiring immediate evaluation to exclude retinoblastoma, a life-threatening malignancy. 1
- Germline testing should be performed for all children with retinoblastoma regardless of laterality or family history. 4
Common Pitfall to Avoid
The description of "stable non-progressive" calcifications might tempt clinicians toward a benign diagnosis, but this is misleading. The presence of calcifications in retinal lesions with leukocoria is the defining feature of retinoblastoma, not a reassuring sign. 1 The stability mentioned in the question likely reflects a short observation period and should not delay definitive diagnosis and treatment.