Imaging Evaluation of Leukocoria

A recent discussion with an ophthalmologist friend prompted research into the topic of appropriate imaging for the evaluation of leukocoria.

Retinoblastoma accounts for 50%-60% of cases of leukocoria in children, followed by persistent hyperplastic primary vitreous, Coats disease, toxocariasis, retinopathy of prematurity, and retinal astrocytic hamartoma. The diagnosis can be made by the ophthalmologist using ophthalmoscopy and ocular ultrasound. Advanced imaging is used when the diagnosis remains uncertain and for evaluating the extent of disease if a diagnosis of retinoblastoma is made.

The European Retinoblastoma Imaging Collaboration (ERIC) has developed consensus guidelines on imaging children with leukocoria. The most important change to the way leukocoria may be currently imaged in some centers is a move away from CT in favor of ultrasound and MRI. This is not only because of general concern about the use of radiation in children, but also the possibility of an additional risk of radiation-induced cancer in patients with hereditary retinoblastoma, who are already at higher risk for developing second primary cancers.

The only supposed benefit of CT, the detection of calcifications, is now matched by improving technology in ultrasound and MRI. Indeed, a recent study showed that combining data from ophthalmoscopy, ultrasound, and MRI resulted in the detection of all calcifications seen by CT.

Ocular ultrasound is usually performed by ophthalmologists with the child under general anesthesia. Calcifications present as highly reflective foci with characteristic acoustic shadowing. Histologically, 95% of retinoblastomas have calcifications, and ultrasound can detect calcifications in 92%–95% of these cases. These calcifications, however, can obscure visualization of the optic nerve, limiting the use of ultrasound in determining risk factors for metastasis.

Ultarsound can also demonstrate retinal detachment, which is important in defining the pattern of tumor growth.

While diagnosis of retinoblastoma can almost always be made with ophthalmoscopy and ocular ultrasound, MRI is the modality of choice for evaluating an intraocular mass and determining disease extent in retinoblastoma (e.g., optic nerve infiltration past the cribriform lamina, infiltration of choroid and sclera, and determination of extraocular and intracranial extension).

ERIC has put together minimal requirements for MRI evaluation of leukocoria in children, the details of which are outlined in the reference below. In brief, high-resolution images of the orbits, eyes, and optic nerves prior to and following intravenous contrast are advocated. The imaging protocol should also include sequences of the whole brain to exclude trilateral retinoblastoma and leptomeningeal metastases.

References

de Graaf P, Göricke S, Rodjan F, Galluzzi P, Maeder P, Castelijns JA, Brisse HJ; on behalf of the European Retinoblastoma Imaging Collaboration (ERIC). Guidelines for imaging retinoblastoma: imaging principles and MRI standardization. Pediatr Radiol. 2011 Aug 18.