High resolution magnetic resonance imaging of retinoblastoma

Abstract

Background/aims: Diagnosis of retinoblastoma is mainly based on indirect ophthalmoscopy, but additional imaging techniques are indispensable for the staging of the disease. A new high resolution magnetic resonance imaging (MRI) technique for the examination of the eye was evaluated. A new surface coil with a diameter of 5 cm allows a field of view of 60 mm with an in-plane resolution of 0.8 mm. We compared preoperative MRI scans with the histology after enucleation in 21 cases of retinoblastoma. Parameters studied were appearance of retinoblastoma, choroidal and scleral infiltration, extraocular extension, optic nerve infiltration, and vitreous seeding.

Results: All retinoblastomas could be visualised as hypointense to vitreous on T2 weighted images and slightly hyperintense to vitreous on plain T1 weighted images with a moderate enhancement after contrast application. Histology revealed seven cases with infiltration of the optic disc or optic nerve. Preoperative MRI scans depict juxtapapillary tumour masses, but it was impossible to differentiate between a juxtapapillary retinoblastoma, a prelaminar infiltration of the optic disc, or a just postlaminar optic nerve infiltration. In five of 14 cases with a proved tumour infiltration of the choroid, MRI scans showed an inhomogeneous contrast enhancement of the choroid in enhanced T1 weighted sequences beneath the retinoblastoma. Whether this sign is specific for a choroidal infiltration or is just an artefact remains unclear. High resolution MRI scans did not allow the exclusion of this form of intraocular tumour extension. All nine cases with proved vitreous seeding were not detected by MRI scans. None of these cases showed scleral infiltration or orbital tumour extension. Therefore, it is not possible to judge the rank of this technique in detecting orbital tumour growth.

Conclusion: The new MRI technique is of limited value in visualisation of prelaminar or postlaminar infiltration of the optic nerve. Advanced choroidal infiltration might be visualised by contrast enhanced T1 weighted MRI scans, but the available spatial resolution did not allow the exclusion this critical form of tumour growth by MRI scans. Nevertheless, high resolution MRI with the new surface coil has superior contrast and spatial resolution compared to computed tomograph (CT) or other available imaging techniques. MRI cannot replace CT in detecting tumour calcification but with increasing experience with this new technique it should be possible to renounce CT scans in the majority of cases of retinoblastoma.

Figure 1

MRI of retinoblastoma (case 3, Table 1). (A) Plain T1 weighted MRI of retinoblastoma. The tumour is slightly hyperintense to vitreous. (B) Contrast enhanced T1 weighted MRI shows moderate enhancement of tumour signal intensity and strong enhancement of the uvea after application of paramagnetic contrast material. Small areas of low signal intensity (arrow) inside the tumour may correspond to calcifications. (C) In T2 weighted images the retinoblastoma is hypointense to vitreous. Hyperintense cerebrospinal fluid inside the subarachnoidal space demarcates the optic nerve (black arrowhead). The tumour beside the optic disc (white arrowhead) was interpreted as suspected infiltration.

Figure 2

Correlation of MRI and histology (case 2, Table 2). (A) Contrast enhanced T1 weighted MRI showed slight infiltration of the optic disc (black arrowhead) and inhomogeneous contrast enhancement of the uveal band (white arrowhead). Histology revealed postlaminar tumour infiltration of the optic nerve ((B) Haematoxylin and eosin staining, ×5) and tumour infiltration of the choroid (C); haematoxylin and eosin staining, ×10.

Figure 3

Contrast enhanced T1 weighted MRI of a small retinoblastoma at the posterior pole showed inhomogeneous contrast enhancement (A) of the uvea beneath the tumour (case 12, Table 2). MRI finding can not be explained by histology with infiltration of the uvea beyond Bruch’s membrane (B) HE staining, ×50.

Figure 4

Contrast enhanced T1 weighted MRI (case 17, Table 2). Recurrence of retinoblastoma after external beam irradiation and chemotherapy. Cystic extension of the subarachniod space around the optic nerve (A) behind the globe was misinterpreted as extraocular tumour extension. Histology (B) showed regressive tumour remnants on the surface of the optic disc. Thickening of the leptomeninges around the optic nerve without extraocular tumour extension. HE staining, ×5.