Teaching Case

A 48-year-old woman, followed-up in the radiotherapy service for undifferentiated carcinoma of the nasopharynx (UCNT), handled by concomitant radiochemotherapy and presented 15 months after the end of the treatment with reduction in left visual acuteness.

Cerebral MRI was made and showed a small hypertrophy of the left second nerve in its pre-chiasmatic portion which showed hyperintense signal on T2WI, and enhanced after injection of gadolinium.

Radiation-induced optic neuropathy (RION) is a rare but generally disastrous repercussion of radiation to the optic pathways. It is essentially an exclusive iatrogenic phenomenon, arising in patients who have had radiation therapy for neoplasms and other lesions in locations near the visual apparatus [1].
The mechanism of this entity implies direct damage to macromolecules and formation of free peroxide and superoxide radicals, especially in the presence of oxygen [2].
Pathologic specimens of involved optic nerve show ischaemic demyelination, axonal loss, reactive astrocytosis, endothelial hyperplasia, oblitrative endarteritis and fibrinoid necrosis [3-5].
Typically, this pathology presents with acute painless visual loss in one or both eyes.
Presentation time of visual symptoms varies from 3 months to 8 years after radiotherapy; nevertheless, nearly all cases arise in the course of 3 years after radiotherapy, with a peak at 1.5 years [3].
MRI is the investigation of choice for diagnosing radiation injury to the visual pathway, and may show abnormalities before the loss of vision. The development of FATSAT techniques and the use of paramagnetic contrast solutions allow good exploration of the optic chiasm and also intraorbital and intracranial parts of the optic nerve. Typically, on T1WI there is no anomaly. After injection, the optic nerve will show enhancement [6].
Enlargement of the optic nerve has also been reported in the literature [7, 8], it may be explained by haemorrhage due to radiation-induced vasculopathy [9].
Optic neuropathy (ON) covers many clinical entities (inflammatory, ischaemic, post-radiation, ...) [10].
Unilateral ON is more suggestive of an inflammatory, ischaemic, post-radiation, traumatic, or compressive process, while bilateral ON generally suggests a toxic, hereditary or metabolic origin [10].
Pain on eye movement associated with a rapid vision loss and a normal fundus is specific of optic neuritis [10].
RION is generally maximum at onset, while Inflammatory ON frequently worsens over a short period of time [10].
The use of DWI to explore the optic nerve is rarely mentioned in the literature. Some authors noted that ADC was increased in the acute inflammatory phase but decreased in the chronic phase of optic neuritis. Recently, the introduction of fat and CSF-suppressed zonal oblique multi-section echoplanar imaging (ZOOM-EPI) sequences has revolutionized the exploration of the optic nerve [11-13].
This technique has been applied by Al-Shafai and Mikulis to a patient with an acute ischaemic ON; the optic nerve of this patient showed decreased ADC [14].
Systemic corticosteroid and hyperbaric oxygen are used for management of this disorder, but the results are discouraging [2].
Prevention of this disorder seems to be more efficient (reduction of radiation doses, daily fractionation of radiotherapy, exact focusing of radiation beam on target tissue, usage of stereotactic methods of radiotherapy...) [2].