The Medial Longitudinal Fasciculus and Internuclear Opthalmoparesis: There’s More Than Meets the Eye

Abstract

Background and purpose The classic sign of a lesion in the medial longitudinal fasciculus is internuclear opthalmoplegia. However, clinical presentation may vary depending on the type of pathology and the lesion location. The purpose of this study was to identify and classify the different lesions of the medial longitudinal fasciculus on MRI and review their clinical presentations. We also offer an overview of the pertinent imaging anatomy of the medial longitudinal fasciculus. Materials and methods Patients with an abnormality affecting the medial longitudinal fasciculus were identified retrospectively using the keyword ‘medial longitudinal fasciculus’ included in radiology reports between 2010 and 2018 using the Nuance mPower software (Nuance Communications, Burlington, MA). The brain MRI examinations of these patients were reviewed by two neuroradiolgists. Detailed description of lesion location within the medial longitudinal fasciculus, pathology type, additional lesions, and clinical presentations were recorded along with pertinent demographic information. Results Five men and four women were identified with lesions in the medial longitudinal fasciculus on brain MRI. Five patients demonstrated demyelination in the medial longitudinal fasiculus and four patients demonstrated findings of an acute cerebrovascular accident. Two-thirds of medial longitudinal fasiculus lesions were located in the upper, mid, or lower pons with the remaining located in the midbrain. Of the patients presenting with a cerebrovascular accident, there was little to no additional evidence of acute stroke elsewhere in the brain. All patients were clinically symptomatic with 89% of patients demonstrating extraocular muscle dysfunction at presentation and 78% of patients experiencing dizziness. Additional symptoms included headache, weakness, and gait instability. Conclusions Lesions involving the medial longitudinal fasiculus may not always present with the classic sign of internuclear opthalmoplegia. Variations in lesion location may result in diplopia rather than internuclear opthalmoplegia, and additional brain lesions may produce clinical symptoms that confound extraocular muscle dysfunction. Lesions affecting the often-overlooked vestibular and otolithic reflexes, which run in the medial longitudinal fasiculus, may result in dizziness/weakness and mask the classic internuclear opthalmoplegia symptoms. The radiologist should carefully inspect the medial longitudinal fasiculus in all patients regardless of the supportive clinical history of extraocular muscle dysfunction since symptoms may be more general than classically described.

Medial longitudinal fasciculus (MLF)-syndrome in a multimorbid patient with alcohol use disorder: a case report

“…Through a careful diagnostic workup, the differential diagnosis was narrowed down to ischemic stroke, which was verified by MRI showing subacute MLF infarct. The MRI notably aligns with the clinical finding of INO with preserved convergence, indicating a unilateral infarction of the MLF near the pontomesencephalic junction ( Figures 1,3 ) ( 4 ).…”

“…Similarly, feelings of lightheadedness, or dizziness, upon mobilization in patients with congestive heart disease could be attributed to cardiovascular insufficiency, namely orthostatic hypotension, clouding the detection of posterior circulation ischemia. Nevertheless, dizziness is common in patients with MLF syndrome as fibers from the contralateral posterior semicircular canal and the utricle travel within the MLF to reach mesencephalic ocular motor neurons responsible for the vestibulo-ocular reflex (VOR) ( 4 , 5 ).…”

Medial longitudinal fasciculus (MLF)-syndrome in a multimorbid patient with alcohol use disorder: a case report

“…Through a careful diagnostic workup, the differential diagnosis was narrowed down to ischemic stroke, which was verified by MRI showing subacute MLF infarct. The MRI notably aligns with the clinical finding of INO with preserved convergence, indicating a unilateral infarction of the MLF near the pontomesencephalic junction ( Figures 1,3 ) ( 4 ).…”

“…Similarly, feelings of lightheadedness, or dizziness, upon mobilization in patients with congestive heart disease could be attributed to cardiovascular insufficiency, namely orthostatic hypotension, clouding the detection of posterior circulation ischemia. Nevertheless, dizziness is common in patients with MLF syndrome as fibers from the contralateral posterior semicircular canal and the utricle travel within the MLF to reach mesencephalic ocular motor neurons responsible for the vestibulo-ocular reflex (VOR) ( 4 , 5 ).…”

MRI-Negative Internuclear Ophthalmoplegia: A Diagnostic Challenge Emphasizing Clinical Localization

“…Convergence was impaired, further localizing the pathology to the rostral midbrain [ 5 ]. The MLF is a heavily myelinated intersegmental tract that links the contralateral oculomotor nucleus in the midbrain and the abducens nucleus in the pons to coordinate conjugate horizontal gaze [ 6 ]. The internuclear fibers connecting the ipsilateral medial rectus subnucleus of CN III to the contralateral abducens nucleus are disrupted by a focal lesion in the MLF, typically in the dorsal pons or midbrain.…”

Lower Motor Neuron Facial Palsy Due to Facial Colliculus Syndrome

“…In our patient, clinically he had features of eight syndrome which suggest involvement of the right facial nucleus (right LMN CN7 palsy), abducens nucleus and MLF (leading to the right congujate gaze palsy). In addition, his vertigo could be attributed to disruption of the vestibular ocular reflexes that also run in the MLF [ 11 ].…”

Medial longitudinal fasciculus (MLF)-syndrome in a multimorbid patient with alcohol use disorder: a case report

“…Through a careful diagnostic workup, the differential diagnosis was narrowed down to ischemic stroke, which was verified by MRI showing subacute MLF infarct. The MRI notably aligns with the clinical finding of INO with preserved convergence, indicating a unilateral infarction of the MLF near the pontomesencephalic junction ( Figures 1,3 ) ( 4 ).…”

“…Similarly, feelings of lightheadedness, or dizziness, upon mobilization in patients with congestive heart disease could be attributed to cardiovascular insufficiency, namely orthostatic hypotension, clouding the detection of posterior circulation ischemia. Nevertheless, dizziness is common in patients with MLF syndrome as fibers from the contralateral posterior semicircular canal and the utricle travel within the MLF to reach mesencephalic ocular motor neurons responsible for the vestibulo-ocular reflex (VOR) ( 4 , 5 ).…”

MRI-Negative Internuclear Ophthalmoplegia: A Diagnostic Challenge Emphasizing Clinical Localization

“…Convergence was impaired, further localizing the pathology to the rostral midbrain [ 5 ]. The MLF is a heavily myelinated intersegmental tract that links the contralateral oculomotor nucleus in the midbrain and the abducens nucleus in the pons to coordinate conjugate horizontal gaze [ 6 ]. The internuclear fibers connecting the ipsilateral medial rectus subnucleus of CN III to the contralateral abducens nucleus are disrupted by a focal lesion in the MLF, typically in the dorsal pons or midbrain.…”

Lower Motor Neuron Facial Palsy Due to Facial Colliculus Syndrome

“…In our patient, clinically he had features of eight syndrome which suggest involvement of the right facial nucleus (right LMN CN7 palsy), abducens nucleus and MLF (leading to the right congujate gaze palsy). In addition, his vertigo could be attributed to disruption of the vestibular ocular reflexes that also run in the MLF [ 11 ].…”

Medial longitudinal fasciculus (MLF)-syndrome in a multimorbid patient with alcohol use disorder: a case report

“…Through a careful diagnostic workup, the differential diagnosis was narrowed down to ischemic stroke, which was verified by MRI showing subacute MLF infarct. The MRI notably aligns with the clinical finding of INO with preserved convergence, indicating a unilateral infarction of the MLF near the pontomesencephalic junction ( Figures 1,3 ) ( 4 ).…”

“…Similarly, feelings of lightheadedness, or dizziness, upon mobilization in patients with congestive heart disease could be attributed to cardiovascular insufficiency, namely orthostatic hypotension, clouding the detection of posterior circulation ischemia. Nevertheless, dizziness is common in patients with MLF syndrome as fibers from the contralateral posterior semicircular canal and the utricle travel within the MLF to reach mesencephalic ocular motor neurons responsible for the vestibulo-ocular reflex (VOR) ( 4 , 5 ).…”

MRI-Negative Internuclear Ophthalmoplegia: A Diagnostic Challenge Emphasizing Clinical Localization

“…Convergence was impaired, further localizing the pathology to the rostral midbrain [ 5 ]. The MLF is a heavily myelinated intersegmental tract that links the contralateral oculomotor nucleus in the midbrain and the abducens nucleus in the pons to coordinate conjugate horizontal gaze [ 6 ]. The internuclear fibers connecting the ipsilateral medial rectus subnucleus of CN III to the contralateral abducens nucleus are disrupted by a focal lesion in the MLF, typically in the dorsal pons or midbrain.…”

Lower Motor Neuron Facial Palsy Due to Facial Colliculus Syndrome

“…In our patient, clinically he had features of eight syndrome which suggest involvement of the right facial nucleus (right LMN CN7 palsy), abducens nucleus and MLF (leading to the right congujate gaze palsy). In addition, his vertigo could be attributed to disruption of the vestibular ocular reflexes that also run in the MLF [ 11 ].…”