Bilateral retinoblastoma in a 8-month-old girl --- MR imaging features

Clinical History

An 8-month-old Asian girl presented with incidental finding of bilateral whitish pupils by her parents. Her antenatal and perinatal history was unremarkable and she otherwise enjoyed good health since birth. Physical examination showed bilateral leukocoria.

Imaging Findings

CT examination of orbits showed bilateral calcified intraocular masses.

MRI of the orbits showed lobulated intraocular masses arising from the retina of both globes, with endophytic protrusion into the vitreous. They were T1 hyperintense and T2 hyperintense compared with the vitreous, with moderate contrast enhancement in T1-weighted post-Gadolinium scan. Small signal voids were noted within the lesions signifying presence of punctate calcifications.

No anterior chamber contrast enhancement was evident. No optic nerve extension or transcleral spread was identified. The rest of the brain including the pineal gland and suprasellar fossa were unremarkable.

Discussion

Retinoblastoma is the most common intraocular tumour in children, with an incidence of one in 17000 births. [1] It is a congenital primary malignant tumour of the retina, and is bilateral in around 25-30% of patients. Patients commonly present with leukocoria at an average age of 18 months. [2] Bilateral disease tends to present earlier (average 13 months). [3] It is a subtype of primitive neuroectodermal tumour (PNET), and is associated with germline mutation of the RB1 tumour-suppressor gene. [4] Optic nerve involvement or extraocular tumour spread would indicate poor prognosis. [5] Of note trilateral disease (bilateral retinoblastoma with pineal tumour) and quadrilateral disease (trilateral disease with suprasellar tumour) carry a dismal prognosis of less than 24 months of survival. [2, 4] Early detection of the tumour is therefore crucial for a favourable outcome.

Imaging studies are the mainstay for diagnosis as biopsy carries a significant risk of tumour seeding. [2] Ultrasonography is commonly used by ophthalmologists for initial imaging assessment of the globes. With the advances of MR imaging, CT examination of orbits is no longer recommended for identifying intraocular calcifications. [1] Together with ultrasound, MR imaging can differentiate retinoblastoma from other differential diagnoses and has an important role in staging and grading the disease. [1, 4]

Retinoblastoma is classically mildly T1 hyperintense and moderately to markedly T2 hypointense when compared to the vitreous. The signal intensity pattern helps to differentiate it from the two other common differential diagnoses of persistent hyperplastic primary vitreous and Coats' disease, which are both T2 hyperintense. [2, 3, 4]

MR imaging is used for assessment of the extent of locoregional disease, extraocular spread or coexisting intracranial tumours. [1, 4] The tumour shows moderate to marked heterogeneous contrast enhancement in T1 post-Gadolinium images. [3] Any contrast enhancement in the anterior segment should be alerted as it is associated with more aggressive tumours. [2] A post contrast scan is also useful for assessing optic nerve and transcleral extension, which are poor prognostic indicators. MR imaging of the whole brain is essential for detection of trilateral, quadrilateral disease and CSF spread. T2W images are also helpful for detecting any complications e.g. retinal detachment. [2, 3, 4]

In conclusion, MR imaging is useful for assessment of patients with retinoblastoma, in particular in assessing locoregional spread, extraocular and intracranial diseases. Together with ultrasound, it is superior to CT scans in diagnosing as well as identifying important prognostic indicators for staging of the disease.

Differential Diagnosis List

Final Diagnosis

Bilateral retinoblastoma

URL:	https://www.eurorad.org/case/10107
DOI:	10.1594/EURORAD/CASE.10107
ISSN:	1563-4086