Mesodiencephalic Stroke Causing Unilateral riMLF and INC Ocular Motor Syndromes

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 65-year-old man who experienced the sudden onset of diplopia (with horizontal and vertical components), dysarthria and imbalance. An MRI performed the following day showed a left mesodiencephalic stroke. The patient was seen in clinic 10 days later (when the video was taken), and by that time the diplopia was purely vertical. The patient had ocular motor findings due to involvement of two distinct rostral midbrain structures: 1) Left interstitial nucleus of Cajal (INC) a. Incomplete ocular tilt reaction including a left hypertropia from skew deviation (25 prism diopters) and ocular counterroll (top poles rotated toward the right ear on dilated fundus exam), but without a head tilt i. The utriculo-ocular motor pathway (or graviceptive pathway, which mediate afferents from utricle and vertical semicircular canal fibers) begins in the right labyrinth, decussates at the pontomedullary junction, and ascends via the left medial longitudinal fasciculus (MLF) to the left INC. The higher eye will be ipsilesional when the utriculo-ocular motor pathway is affected rostral to (or higher than) the decussation of this pathway - this can be remembered as HIGH-HIGH. If the lesion is lower than the decussation, the lower eye will be ipsilesional - this can be remembered as LOW-LOW. b. Vertical gaze-evoked nystagmus (but none horizontally) i. The INC is responsible for vertical and torsional gaze holding, while the medullary nucleus prepositus hypoglossi-medial vestibular nucleus complex is responsible for horizontal gaze holding 2) Left rostral interstitial MLF (riMLF) a. Torsional nystagmus, top poles beating toward the RIGHT ear (with torsional nystagmus associated with a LEFT INC, the top poles should beat ipsilaterally, or top poles toward the LEFT ear). With a unilateral riMLF lesion, if torsional nystagmus is seen, it will beat contralaterally as in this case. b. Slow vertical saccades, slower downward compared to upward. This is because the innervation for upward saccades is bilateral (i.e., unilateral riMLF innervates bilateral superior rectus and inferior oblique) while the innervation for downward saccades is unilateral (i.e., unilateral riMLF innervates ipsilateral inferior rectus and superior oblique). The riMLF contains the vertical and torsional excitatory burst neurons. Vertical smooth pursuit and vertical vestibulo-ocular reflexes were normal. c. Absent ipsitorsional quick phases in the roll plane when the patient's head was slowly tilted to the left side. When his head is tilted slowly to the right, the eyes will counterroll with top poles toward the left ear due to the physiologic ocular tilt reaction, but as the head continues to tilt, a quick torsional phase will need to be generated toward the right ear. Since the riMLF contains the vertical and torsional burst neurons, quick torsional phases toward the left (ipsilesional) ear cannot be generated with a left head tilt in this patient, although they were normal with head tilt to the right side due to the intact right riMLF. The initial diplopia with vertical AND horizontal components may have been related to skew deviation AND a pseudo-abducens palsy on the RIGHT (since the descending inhibitory convergence pathways decussate from the left mesodiencephalic region to innervate the right medial rectus subnucleus), respectively. Or, there may have been 3rd fascicle or nuclear involvement initially causing medial rectus weakness. However, this is purely conjecture because no detailed ocular motor examination was available in the hospital records. The patient was seen 1 month later and at that time there had been significant improvement in his skew deviation, and spontaneous torsional nystagmus had resolved completely. Three months after the stroke, there was no vertical misalignment in straight ahead gaze, although there was still a small left hypertropia in downgaze. However, his slow vertical saccades remained. The patient also happened to have asteroid hyalosis in the vitreous OD much more than OS (apparent in the video). 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This is a 65 year-old man who experienced the sudden onset of diplopia, dysarthria and imbalance. An MRI performed the following day showed a left rostral midbrain stroke. The patient was seen in clinic 10 days later (when the video was taken), and by that time the diplopia was purely vertical. The patient had ocular motor findings due to involvement of two distinct rostral midbrain structures: 1) Left interstitial nucleus of Cajal (INC) a. Incomplete ocular tilt reaction including a left hypertropia from skew deviation (25 prism diopters) and ocular counterroll (top poles rotated toward the right ear on dilated fundus exam), but without a head tilt - this was due to involvement of the utriculo-ocular motor pathway. b. Vertical gaze-evoked nystagmus - the INC is responsible for vertical and torsional gaze holding, while the medullary nucleus prepositus hypoglossi-medial vestibular nucleus complex is responsible for horizontal gaze holding. 2) Left rostral interstitial MLF (riMLF) a. Torsional nystagmus, top poles beating toward the RIGHT ear (with torsional nystagmus associated with a LEFT INC, the top poles should beat ipsilaterally, or top poles toward the LEFT ear). With a unilateral riMLF lesion, if torsional nystagmus is seen, it will beat contralaterally as in this case. b. Slow vertical saccades, slower downward compared to upward. This is because the innervation for upward saccades is bilateral (i.e., unilateral riMLF innervates bilateral superior rectus and inferior oblique) while the innervation for downward saccades is unilateral (i.e., unilateral riMLF innervates ipsilateral inferior rectus and superior oblique). c. Absent ipsitorsional quick phases in the roll plane when the patient's head was slowly tilted to the left side. When his head is tilted slowly to the right, the eyes will counterroll with top poles toward the left ear due to the physiologic ocular tilt reaction, but as the head continues to tilt, a quick torsional phase will need to be generated toward the right ear. Since the riMLF contains the vertical and torsional burst neurons, quick torsional phases toward the left (ipsilesional) ear cannot be generated with a left head tilt in this patient, although they were normal with head tilt to the right side due to the intact right riMLF. Three months after the stroke, there was no vertical misalignment in straight ahead gaze, although there was still a small left hypertropia in downgaze. However, his slow vertical saccades remained. The patient also happened to have asteroid hyalosis in the vitreous OD much more than OS (apparent in the video). https://collections. lib.utah.edu/ark:/87278/s6mm0pz4