Ocular Ultrasound is the Best Initial Imaging Study
For a 2-year-old with leukocoria (white pupil) and squint, ocular ultrasound is the appropriate initial imaging modality, performed by the pediatric ophthalmologist during the urgent specialist evaluation. 1, 2
Immediate Action: Urgent Ophthalmology Referral Without Imaging
- The child requires immediate referral to a pediatric ophthalmologist without delay for additional testing or imaging in the primary care setting. 2, 3
- The American Academy of Pediatrics states that absent red reflex is an absolute indication for specialist evaluation, as conditions like retinoblastoma or dense congenital cataract can result in permanent vision loss or death if treatment is postponed. 2
- Leukocoria represents a vision-threatening and potentially life-threatening emergency that demands urgent ophthalmologic assessment before any imaging is ordered. 2, 3
Why Ultrasound is the Correct Initial Imaging
Ocular ultrasound (B-scan) is the imaging modality of choice when the ophthalmologist cannot directly visualize the posterior segment due to media opacity: 1, 2, 4
- Ultrasound can characterize intraocular pathology, detect calcifications (highly suggestive of retinoblastoma), and assess for retinal detachment or other structural abnormalities. 1, 4
- It is performed by the ophthalmologist as part of the comprehensive evaluation and does not require sedation or radiation exposure. 4
- Ultrasound can differentiate between retinoblastoma (which shows calcification) and other causes of leukocoria such as persistent hyperplastic primary vitreous (PHPV), Coats disease, or cataract. 1, 4
Why Other Imaging Modalities Are Not Initial Studies
CT scan should be avoided as initial imaging: 5
- CT exposes children to radiation, which is particularly concerning in retinoblastoma patients who have increased risk of second malignancies. 5
- While CT can detect calcifications, ultrasound provides this information without radiation exposure. 1, 5
MRI is reserved for specific indications, not initial evaluation: 1
- MRI of the head and orbits with and without IV contrast is indicated when retinoblastoma is confirmed and staging for extraocular extension, optic nerve involvement, or intracranial spread is needed. 1
- The American College of Radiology recommends MRI as the most useful imaging for malignant intraocular masses, but this follows the initial clinical and ultrasound evaluation. 1
X-ray has no role in evaluating leukocoria. 1
Critical Differential Diagnosis
The most common causes of leukocoria in children are: 4, 6
- Congenital cataract (79.76% of cases) - lens opacity blocking light transmission 4
- Retinoblastoma (12.5% of cases) - life-threatening malignancy requiring urgent diagnosis 4, 6
- Coats disease (3.5%) - retinal vascular abnormality 4
- Retinal detachment (2.9%) 4
- Persistent hyperplastic primary vitreous (PHPV) (1.1%) 4, 6
Essential Ophthalmologic Evaluation Components
The pediatric ophthalmologist will perform: 2, 3
- Cycloplegic refraction to accurately determine refractive error and assess for media opacities 2, 3
- Detailed funduscopic examination under dilation to evaluate the posterior segment and definitively exclude retinoblastoma 2, 3
- Ocular ultrasound (B-scan) when direct visualization is blocked by media opacity 1, 2, 4
- Examination under anesthesia (EUA) if the child is uncooperative for adequate fundus examination 4
Common Clinical Pitfall
Never assume the diagnosis is benign simply because the child is developing normally. 2
- Both congenital cataract and retinoblastoma can present with normal systemic development while causing severe unilateral visual impairment. 2
- The presence of squint (strabismus) with leukocoria suggests sensory esotropia secondary to structural pathology, making urgent evaluation even more critical. 3, 6
Answer: C. Ultrasound - performed by the ophthalmologist during urgent specialist evaluation, not ordered from primary care.