Unilateral Internuclear Ophthalmoplegia following Minor Head Injury

A lesion in the medial longitudinal fasciculus (MLF) causes internuclear ophthalmoplegia (INO). Many intracranial lesions, such as multiple sclerosis or vascular disorders may be associated with INO; however, INO is a rare complication of minor head injury. The mechanism underlying injury to the MLF may be shear force on the brain stem during head trauma. The shear force can tear or stretch the fibers of the MLF and can also lead to compromise or rupture of the perforating branches of the basilar artery. We present an unusual case of unilateral INO after minor head injury in a patient with a small site of hemorrhage in the midline of the pontomesencephalic junction, confirmed by brain magnetic resonance imaging using susceptibility-weighted imaging.