Superior oblique myokymia: magnetic resonance imaging support for the neurovascular compression hypothesis. Yousry I, Dieterich M, Naidich TP, Schmid UD, Yousry TA. Ann Neurol 2002;51:361–368

Abstract

Superior oblique myokymia (SOM) is a rare recurring disorder of ocular motility characterized by unilateral paroxysmal oscillopsia and microtremor. Visible structural lesions on conventional magnetic resonance imaging (MRI) are rarely demonstrated as causal of SOM. It has been hypothesized that vascular compression of the trochlear nerve may be a common cause of SOM. Direct display of such neurovascular compression by MRI has been lacking. The goal of this study was to assess the presence of neurovascular contacts in patients with SOM, using a specific MRI protocol. A total of six patients with right SOM underwent detailed neuroophthalmological examination, which showed tonic or phasic eye movements diagnostic of SOM. All patients underwent MRI using a MRI Fourier transform constructive interference in steady-state sequence in combination with MRI time of flight magnetic resonance angiography, both before and after the administration of gadolinium. With this protocol, the trochlear nerve could be visualized on 11 of 12 sides (92%). Arterial contact was detected at the root exit zone of the symptomatic right trochlear nerve in all six patients (100%). No arterial contact was identified at the root exit zone of the asymptomatic left trochlear nerve in any of the five left nerves visualized. The authors conclude that SOM can result from neurovascular contact at the root exit zone of the trochlear nerve and that SOM should therefore be considered among the neurovascular compression syndromes. This may have implications regarding possible surgical intervention for microvascular decompression.—Nancy J. Newman