Involved lesion
Case 90
【Progress】He was given anti-hypertension agent. Oculomotor nerve palsy remained one month after the stroke onset.
【Discussion】
Medial longitudinal fasciculus (MLF) is found along with reticular body in brain stem. MLF situates as a pair near the midline of the brain stem adjacent with the fourth ventricle. MLF connects three major nerve nuclei: oculomotor nerve nucleus, trochlear nerve nucleus and abducens nerve nucleus, as well as vestibulocochlear nerve. MLF contains a set of crossed fibers with ascending and descending fibers and functions to integrate movements of the eyes: especially voluntary eye gaze movement and conjugate horizontal gaze. MLF functions to integrate movements of the eyes and head movements.
When MLF damages, it is called internuclear eye movement disorder (ophthalmoplegia). A lesion affecting MLF is characterized by an ipsilateral slow adducting saccade (paralytic adducting eye ball movement), contralateral abducting nystagmus, an ipsilateral adduction deficit (1). Our patient experienced diplopia and ptosis of the right eye. It is reported that approximately a half of the patients with internal carotid dissection aneurysm had Horner syndrome and approximately a third of the patients with brain stem lesion demonstrated Horner syndrome (2, 3). Our patient was suspected to have internal carotid aneurysm but he did not. Instead, brain MRI showed a brain stem lesion: acute lacunar infarction corresponded to the left MLF.
Pons is divided into three parts: upper, middle and lower parts. Middle part of Pons is mainly blood-supplied by branches from basilar arteries: paramedian branches, short circumferential branches and long circumferential branches which supplies medial antero-lateral and lateral portion of the middle part of Pons, respectively. Meanwhile, the upper part of the pons gets the blood supply by branches from basilar artery as well as superior cerebellar artery which supplies the lateral portion of the upper part of pons. Further, the lower part of pons gets the blood supply by branches from basilar artery as well as anterior inferior cerebellar artery which supplies the lateral portion of the lower part of the pons. Long circumferential artery anastomoses to branches from superior cerebellar artery and anterior inferior cerebellar artery (4, 5). In our case, the stroke of MLF was shown in MRI. MLF situates at bilateral midline of the pons, implying the selective occlusion of paramedian branch of the basilar artery.
【Summary】
We present a fifty six-year-old male with sudden onset of diplopia and ptosis of the right eye. MRI showed high signal intensity of left midline site of the pons corresponded to the left MLF, indicating fresh infarction. We should keep in mind that MFL situates in the midline of pons and midbrain and functions voluntary eye gaze movement by connecting three nerve nuclei: oculomotor nerve nucleus, trochlear nerve nucleus and abducens nerve nucleus. Pons is blood-supplied from branches of basilar artery: paramedian branch, short circumferential branch, lateral circumferential branch, and branches of superior cerebellar artery and anterior inferior cerebellar artery which supplies lateral part of the upper pons and lower pons, respectively.
【References】
1.Hubloue I, et al. A rare case of diplopia: medial inferior pontine syndrome or Foville's syndrome". Eur J Emerg Med. 1996;3 : 194–8. doi:10.1097/00063110-199609000-00011. PMID 9023501. Bassetti C et al. Isolated infarcts of the pons. Neurology. 1996 Jan;46(1):165-75.
2.Krasnianski M, et al. Correlation of clinical and magnetic resonance imaging findings in patients with brainstem infarction. Fortschr Neurol Psychiatr. 2001 May. 69(5):236-41.
3.Biousse V, et al. Ophthalmologic manifestations of internal carotid artery dissection. Am J Ophthalmol. 1998 Oct. 126(4):565-77. [Medline]
4.Schmahmann JD et al. The human basis pontis: motor syndromes and topographic organization. Brain. 2004 Jun;127(Pt 6):1269-91. Epub 2004 May 5.
5.Bassetti C et al. Isolated infarcts of the pons. Neurology. 1996 Jan;46(1):165-75.
2018.1.31