Topics

Topic

design image
Medial longitudinal fasciculus

The medial longitudinal fasciculus (MLF) is a vital paired bundle of nerve fibers located near the midline of the brainstem. It plays a critical role in coordinating eye movements and integrating vestibular (balance) signals with ocular motor function. The MLF is crucial for conjugate gaze and connects various cranial nerve nuclei involved in horizontal and vertical eye movements. Lesions in the MLF often result in distinctive clinical syndromes such as internuclear ophthalmoplegia.

Synonyms

  • MLF

  • Fasciculus longitudinalis medialis

  • Medial longitudinal bundle

Arterial Supply

  • Supplied primarily by paramedian branches of the basilar artery.

  • Additional contributions from the anterior spinal artery (especially in the caudal brainstem).

  • In the midbrain, branches from the posterior cerebral artery may also supply the MLF.

Venous Drainage

  • Drained via small veins of the brainstem, ultimately reaching the basal vein of Rosenthal and the petrosal sinuses.

  • Venous outflow also communicates with the internal cerebral veins.

Function

  • Coordinates horizontal and vertical conjugate eye movements.

  • Integrates vestibular input with eye movement via connections between:

    • Abducens nucleus (VI)

    • Oculomotor nucleus (III)

    • Trochlear nucleus (IV)

    • Vestibular nuclei

  • Involved in the vestibulo-ocular reflex (VOR).

  • Lesions cause internuclear ophthalmoplegia (INO).

MRI Appearance

  • T2-weighted: MLF is not directly visible but can be inferred as a small paired structure near the midline, anterior to the fourth ventricle/aqueduct; lesions (e.g., demyelination in MS) appear as high signal foci.

  • T1-weighted: Usually isointense to surrounding brainstem tissue; abnormality may be subtle unless there is associated hemorrhage or chronic gliosis.

  • FLAIR: Lesions appear as hyperintense foci along the expected course of the MLF, best appreciated in demyelinating disease.

CT Appearance

  • MLF is not visible on non-contrast CT under normal conditions due to its small size and location.

MRI images

Medial longitudinal fasciculus mri 3t axial image