Anterior chamber enhancement predicts optic nerve infiltration in retinoblastoma.

OBJECTIVES: As described recently, intravenously injected gadolinium-based contrast agent (GBCA) penetrates into the anterior eye chamber (AC) and is drained from the retina to the distal optic nerve (ON) along perivascular spaces, which serves retinal homeostasis and was termed the orbital glymphatic system (GS). Independently, AC enhancement predicted ON infiltration, a major risk factor for advanced retinoblastoma (RB), in a small RB patient cohort. We aimed to review the supposed imaging biomarker for ON infiltration in a large RB cohort and with respect to the recently described orbital GS. METHODS: This IRB-approved retrospective single-center study encompassed 539 orbital MRIs performed with an orbital coil and with the children under general anesthesia. Differences of signal intensity ratios (∆SIRs) of the AC to the lens were determined between non-contrast and GBCA-enhanced T1-weighted images and were correlated with histopathologic presence of ON infiltration. RESULTS: ∆SIR of the RB eye was an independent, significant predictor for ON invasion in multivariate analysis with adjustment for tumor size (p < 0.05) and increased with infiltration level. CONCLUSIONS: GBCA enhancement of the AC predicts ON infiltration. This might be caused by impairment of the orbital glymphatic system, which is supposed to clear toxic metabolites from the retina to the postlaminar ON. In RB with ON infiltration, this efflux path is likely to be inhibited, which is supposed to result in disturbed retinal homeostasis, release of vascular endothelial growth factor, and iris neovascularization, which increases penetration of GBCA into the AC. KEY POINTS: • Infiltration of the optic nerve can be predicted by anterior chamber enhancement after intravenous MRI contrast agent administration. • Increased anterior chamber enhancement in retinoblastoma with optic nerve infiltration might result from dysfunction of the orbital glymphatic system with disturbance of retinal homeostasis and consecutive iris neovascularization.

The anterior eye chamber: entry of the natural excretion pathway of gadolinium contrast agents?

OBJECTIVE: Previous studies provided evidence that gadolinium can be found in the aqueous chamber (AC) of the eye several hours post injection (p.i.) of gadolinium-based contrast agents (GBCAs). This study aimed to investigate whether gadolinium can be detected promptly after injection of a macrocyclic GBCA on contrast-enhanced T1-weighted MRI in the AC of children. METHODS: This retrospective study encompassed MRI of 200 healthy eyes of children suffering from retinoblastoma of the contralateral eye. MRI was performed with an orbital coil with the children in a state of general anesthesia. Differences of signal intensity ratios (∆SIRs) of the AC to the lens were determined between pre and post contrast-enhanced T1-weighted images (Dotarem®, Guerbet, 0.1 ml/kg body weight, mean (standard deviation) p.i. time = 12:24 (± 2:31) min). RESULTS: A highly significant signal intensity increase was found in the AC of healthy eyes 12 min after GBCA injection (median ∆SIR (interquartile range) = + 0.08 (0.05-0.12), p < 0.0001). In addition, gadolinium enhancement showed a strong negative correlation with children's age in multivariate analysis with adjustment for p.i. time (p < 0.0001). CONCLUSIONS: GBCA leakage into the AC of healthy infantile eyes was found promptly after injection. The negative correlation between patient age and GBCA enhancement might be explained by a maturation process of the blood-aqueous barrier or Schlemm's canal. Future studies should assess the duration and potential diagnostic applications as well as possible safety concerns of gadolinium presence in the AC. KEY POINTS: • Leakage of gadolinium-based contrast agent into the aqueous chamber of infantile eyes was found promptly after intravenous injection (p < 0.0001). • Gadolinium enhancement of the anterior eye chamber was negatively correlated with the children's age (p < 0.0001).