A 2-year-old child presents with leukocoria and strabismus. On examination, a white reflex is noted in the right eye. What is the investigation of choice to confirm the diagnosis and assess the extent of intraocular disease?

Explanation

## Investigation of Choice in Suspected Retinoblastoma ### Clinical Context Leukocoria (white pupil reflex) and strabismus are classic presenting signs of retinoblastoma. Once clinical suspicion is raised, the next step is direct visualization of the intraocular tumor. ### Why Dilated Fundoscopy Under GA with Indirect Ophthalmoscopy is Correct **Key Point:** Indirect ophthalmoscopy under general anesthesia is the gold standard for initial confirmation and assessment of intraocular disease in retinoblastoma. It allows: - Direct visualization of the tumor, its location, size, and extent - Assessment of vitreous involvement and seeding - Evaluation of the optic disc and macula involvement - Documentation for baseline and follow-up monitoring **High-Yield:** This is the first imaging modality after clinical suspicion because it is non-invasive, provides excellent intraocular detail, and guides further management decisions (chemotherapy vs. enucleation vs. radiation). ### Why Other Options Are Incorrect | Investigation | Role in Retinoblastoma | |---|---| | **B-scan ultrasonography** | Used when media opacity prevents fundoscopy (e.g., dense cataract or vitreous hemorrhage); not first-line for diagnosis | | **MRI of orbits and brain** | Used for staging (extraocular extension, optic nerve involvement, pineal involvement in bilateral cases); NOT for initial intraocular assessment | | **CT of head and orbits** | Useful for detecting calcification and orbital extension; inferior to MRI for soft tissue detail; not first-line for diagnosis | **Clinical Pearl:** Retinoblastoma typically shows calcification on CT in ~70% of cases, but CT is reserved for staging after diagnosis is confirmed on ophthalmoscopy. MRI is preferred over CT for orbital and CNS staging due to better soft tissue contrast and no radiation exposure in a pediatric patient. ### Diagnostic Algorithm ```mermaid flowchart TD A[Leukocoria/Strabismus]:::outcome --> B[Dilated fundoscopy under GA]:::action B --> C{Intraocular tumor seen?}:::decision C -->|Yes| D[Confirm retinoblastoma]:::outcome D --> E[MRI orbits + brain for staging]:::action C -->|No| F[B-scan if media opaque]:::action E --> G{Unilateral or bilateral?}:::decision G -->|Unilateral| H[Assess for extraocular extension]:::action G -->|Bilateral| I[Evaluate for pineal involvement]:::action ``` **Mnemonic:** **FIND RB** = **F**undoscopy (first), **I**maging (MRI for staging), **N**eed GA, **D**iagnosis confirmed, **R**etinoblastoma, **B**ilateral assessment.