Oculomotor nerve (third cranial nerve or III) palsy is a relatively frequent cause of consultation in ophthalmology. It may reveal a life-threatening pathology such as aneurysm rupture, pituitary apoplexy, and therefore need imaging in emergency. Apart from few extreme emergency situations, MRI of the oculomotor tract is the first-line examination required. In the usual clinical practice, the investigators noticed in several patients unusual areas of high-intensity signal within the oculomotor nerve on T2 sequence, observed in various locations along the nerve path (cavernous and/ or intra-orbital segment). This abnormal signal, at the best knowledge of the investigators, has never been reported in the literature and could confirm the nerve impairment. In patients with ophthalmoplegia involving probably the third cranial nerve, disclosing this new MRI sign could help (i) to confirm the involvement of the oculomotor nerve and eliminate differential diagnoses such as myasthenia (ii) to orientate the etiological diagnosis (inflammatory or ischemic origin). A T2 sequence focused on the III could thus be systematically included in the usual MRI protocol.
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High-intensity signal of the oculomotor nerve on MRI T2 sequence (presence or absence, determined by a radiologist)
Timeframe: Baseline