MRI can help diagnose radiation-induced optic neuropathy

This case series documents the clinical characteristics of patients with radiation-induced optic neuropathy.

Study design

The authors compiled details of vision loss, including the temporal relationship to radiation, in 12 patients (15 eyes) who were treated at the University of Michigan Neuro-Ophthalmology Clinic. All patients had undergone 3D-conformal linear accelerator (photon) external beam radiation.

Outcomes

Visual loss was often acute, profound and monocular, but declined slowly after onset over many months without recovery. Three patients eventually developed bilateral disease. All patients demonstrated an afferent pupillary defect at the time of presentation. Affected optic discs were often pale at the time of first visual symptoms, suggesting that subclinical damage had been present for several weeks.

The onset of vision loss occurred at a mean of 18 months (7–48 months) from completion of radiation to onset of vision loss. High-resolution MRI imaging showed a discrete region of enhancement of the affected prechiasmatic optic nerve, often with expansion and high T2 signal in the enhancing segment. The timing of enhancement on imaging varied widely; in some cases, it preceded vision loss while in others it was only noted 7 months after vision loss.

Limitations

This study was limited by its retrospective nature and small sample size.

Clinical significance

The authors concluded that their study further delineates the profile of radiation optic neuropathy. Recognition of imaging characteristics such as enhancement on MRI could assists in diagnosing this condition.