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Neuroradiology Case of the Week

Case 285

Ashwani K. Sharma, MD and Henry Z. Wang, MD, PhD

Clinical Presentation: Patient is a 25-year-old male who presented with symptoms of internuclear ophthalmoplegia. There is clinical suspicion of multiple sclerosis.

Imaging Findings: The sixth cranial nerve (abducens) nucleus lies dorsally in the pons near the genu of the seventh cranial nerve or the region of the facial colliculus. The nucleus innervates the ipsilateral lateral rectus and sends interneurons to the medial longitudinal fasciculus (MLF) that will go on to innervate the contralateral medial rectus to coordinate horizontal gaze. Any signal alteration or contrast enhancement can be seen in the pathway of MLF. Any mass effect from a tumor or vascular or traumatic lesion could present in the similar way.

Diagnosis: Demyelinating lesion of medial longitudinal fasciculus

Discussion: Variety of ocular motor deficits are encountered in patients with MS. These deficits range from isolated nuclear or fascicular cranial nerve palsies to bilateral internuclear ophthalmoplegias (INOs) [1]. A lesion of the medial longitudinal fasciculus results in an ipsilateral adduction deficit and a contralateral abducting nystagmus, referred to as an internuclear ophthalmoplegia (INO). Nystagmus is a frequent ocular motor deficit in MS. Although INO is the most common, other forms include vertical (both upbeat and downbeat), vestibular, pendular, periodic alternating, and gaze-evoked nystagmus. Acquired pendular nystagmus, characterized by oscillations of similar velocity and range, may be seen in the presence of marked loss of visual acuity and is frequently a cause for acquired oscillopsia in MS1. Internuclear ophthalmoplegia is one of the neuro-ophthalmologic hallmarks of MS and is present in 17-41% of patients [2]. INO is characterized by abnormal horizontal ocular movement with lost or limited adduction in the ipsilateral eye and a horizontal abducting nystagmus of the contralateral eye. These signs result from lesions involving the medial longitudinal fasciculus and may be either unilateral or bilateral. About a third of all patients with INO were found to have MS in studies, and an increased risk of MS is associated with bilateral INO [3,4].
     The differential diagnosis for the cause of INO includes infarcts, infections, tumor, hemorrhage, vasculitis, and trauma.

References:

1. Chen L, Gordon LK. Ocular manifestations of multiple sclerosis. Curr Opin Ophthalmol. 2005 Oct;16(5):315-20. [Medline]
2. Tsuda H, Ishikawa H, Matsunaga H, Mizutani T. A neuro-ophthalmological analysis in 80 cases of multiple sclerosis [in Japanese]. Rinsho Shinkeigaku. 2004 Aug;44(8):513-21. [Medline]
3. Bolaños I, Lozano D, Cantú C. Internuclear ophthalmoplegia: causes and long-term follow-up in 65 patients. Acta Neurol Scand. 2004 Sep;110(3):161-5. [Medline]
4. Keane JR. Internuclear ophthalmoplegia: unusual causes in 114 of 410 patients. Arch Neurol. 2005 May;62(5):714-7. [Medline]