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26 Figure 64: The Course of the 3rd (III) NerveThe 3rd nucleus lies at the ventral border of the periaqueductal gray matter, at the level of the superior colliculus. In between the two nuclei is the midline central caudal nucleus (CCN), which innervates bilateral levator palpebrae muscles (explaining how a unilateral nuclear 3rd can cause bilate...Image
27 Figure 65: Vascular Distribution and Anatomy (Including 3rd Nerve) of the Rostral MidbrainIn this axial section of the midbrain at the level of the superior colliculus, the paired 3rd nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located in between. The fascicles that exit the IIIrd nuclei carry the fibers destined to innervate the...Image
28 Figure 68: The Course of the 4th (IV) NerveThe 4th nucleus lies at the ventral border of the periaqueductal gray matter, at the level of the inferior colliculus. The fascicles exit the nucleus dorsally and decussate at the anterior medullary velum (anterior floor of the fourth ventricle), and then exit the brainstem dorsally. The peripheral ...Image
29 Figure 69: Vascular Distribution and Anatomy (Including 4th Nerve) of the Caudal MidbrainIn this axial section of the midbrain at the level of the inferior colliculus, the 4th nuclei are located ventral to the periaqueductal grey, dorsal to the medial longitudinal fasciculus (MLF) and medial to the oculosympathetic tract. Fascicles exit the nucleus dorsally and decussate at the anterior...Image
30 Figure 80: Vascular Distribution and Anatomy Relevant to the Medial Medullary SyndromeThis axial section of the medulla highlights those structures that, when damaged, are often responsible for spontaneous upbeat nystagmus (UBN). The nucleus of Roller and nucleus intercalatus normally have an inhibitory influence over the cerebellar flocculus, and when there is a lesion of Roller/int...Image
31 CANVAS (Cerebellar Ataxia, Neuropathy, and Vestibular Areflexia Syndrome) Video Head Impulse Test (vHIT) FigureCANVAS (Cerebellar Ataxia, Neuropathy, and Vestibular Areflexia Syndrome) is a genetic condition consisting of slowly progressive late-onset ataxia, bilateral vestibulopathy, sensory neuropathy, chronic cough, and autonomic dysfunction. While the term vestibular areflexia typically implies bilateral...Image
32 An Approach to the Patient with (Recent Onset) Spontaneous Episodic Vestibular Syndrome𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: A vascular etiology should always be on the differential diagnosis of the recent onset of the spontaneous (unprovoked) episodic vestibular syndrome (EVS), especially in the older population and when vascular risk factors ...Image
33 An Approach to the Patient with Acute Onset Prolonged Vertigo𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: A vascular etiology should always be on the differential diagnosis of the acute onset prolonged vertigo, especially in the older population and when vascular risk factors are present. However, young patients can suffer fr...Image
34 The Utriculo-Ocular Motor Pathways - Physiologic and Pathologic Ocular Tilt Reaction: OTR Diagram Pathologic EOMs Labelled (Figure 3)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...Image
35 The Utriculo-Ocular Motor Pathways - Physiologic and Pathologic Ocular Tilt Reaction: Pathologic OTR (Figure 2)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...Image
36 The Utriculo-Ocular Motor Pathways - Physiologic and Pathologic Ocular Tilt Reaction: Physiologic Ocular Tilt Reaction (OTR) (Figure 1)A skew deviation is a non-paralytic vertical ocular misalignment that is due to imbalance in the utriculo-ocular motor pathways. While vestibular jerk nystagmus is a consequence of static semicircular canal pathway imbalance (e.g., left-beating nystagmus due to acute right vestibular hypofunction fr...Image
37 Oculopalatal Tremor with Prominent Nystagmus, Bilateral Horizontal Gaze Palsy, and Bilateral Facial Palsies (Figure 1)Figure 1, MRI T2 sequence demonstrating hyperintensities involving bilateral inferior olives of the medulla. This is a 50-year-old woman who experienced the acute onset of right sixth and seventh nerve palsies and left hemiparesis. Two cavernomas within the right pons (one in the region of the facia...Image
38 Periodic Alternating Nystagmus Due to Nodulus Stroke (Figure 1)This is a 70-year-old woman who experienced the acute onset of vertigo and imbalance. MRI demonstrated a diffusion-weighted imaging hyperintensity involving the nodulus (with corresponding ADC hypointensity) consistent with an acute stroke. On examination several weeks after the stroke, periodic alt...Image
39 Neuro-Ophthalmic Features and Pseudo-MG Lid Signs in Miller Fisher Syndrome (Figure 1)This is a 51-year-old woman who presented with imbalance, acute onset dizziness and diplopia that developed over three days following two weeks of upper respiratory infection and bacterial conjunctivitis. When she was initially seen as an outpatient, nystagmus was noted to the right and left, and a ...Image
40 Relationship Between Semicircular Canals and Extraocular MusclesFigure 1: When stimulated, each of the 6 angular acceleration detecting semicircular canals (3 on the right and 3 on the left) responds with a conjugate eye movement, with the vector(s) indicated below. PC=posterior canal; HC=horizontal (also known as lateral) canal; AC=anterior (also known as super...Image
41 Subtle Torsional Pendular Nystagmus in Oculopalatal Tremor (OPT) (Figure 1)This is a 50-year-old woman who presented with imbalance, and MRI demonstrated a right cerebellar cavernous malformation. She underwent surgery to resect the malformation, and post-operatively experienced right hemiparesis and ataxia. Six months after the surgery, balance worsened and vision became ...Image
42 Triangle of Guillain-MollaretSeen here is a schematic representation of the Gullain-Mollaret triangle (Figure 1), also referred to as the dentato-olivary pathway, reflecting the 3 points of this imaginary triangle - 1) dentate nucleus, 2) red nucleus, and 3) inferior olivary nucleus. The olive sends decussating climbing fibers ...Image
43 Ocular Motor & Vestibular Features of the MLF Syndrome (Figures 1, 2, and 3)This 61-year-old woman with HTN and DM presented for evaluation of acute onset diagonal diplopia. Adduction OS was about 60% of normal while medialization OS improved with convergence. In right gaze, dissociated abducting nystagmus was present OD, and there was a clear adduction lag when asking he...Image
44 Using Video Head Impulse Testing to Unmask Covert Saccades in Compensated Vestibular Neuritis (Figures 1 and 2)This is a 30-year-old woman who experienced the acute vestibular syndrome (prolonged vertigo for >24 hours, nausea, unsteadiness, spontaneous nystagmus, head motion intolerance) and was diagnosed with vestibular neuritis. This diagnosis was based on a positive head impulse test to the left (see Figu...Image
45 Vestibular Neuritis with + Head Impulse Test and Unidirectional Nystagmus (Figure 1)Vestibular neuritis is the most common cause of the acute vestibular syndrome, which is characterized by continuous vertigo and spontaneous nystagmus lasting days. It may be mimicked by central causes, including stroke, but in the hands of subspecialists, the HINTS+ (Head Impulse, Nystagmus, Test of...Image
46 Central Anatomy of the Third NerveSeen here is an axial section of the midbrain at the level of the superior colliculus. The paired nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located between the right and left nuclei. The CCN sends projections to bilateral levator palpebrae...Image
47 Saccadic Pathways in the Brainstem and Cerebellum & Mechanism for Saccadic Dysmetria in Wallenberg Syndrome - Normal Function of the Brainstem/Cerebellar Saccadic PathwaysThe inferior cerebellar peduncle (ICP) carries climbing fibers to the dorsal vermis, and these fibers have an inhibitory influence over the Purkinje cells. These Purkinje cells normally inhibit the ipsilateral fastigial nucleus, and the fastigial nucleus projects to the contralateral inhibitory burs...Image
48 Saccadic Pathways in the Brainstem and Cerebellum & Mechanism for Saccadic Dysmetria in Wallenberg Syndrome - Abnormal Function of the Brainstem/Cerebellar Saccadic Pathways with a Left Wallenberg SyndromeThe end result of a lesion involving the climbing fibers within the left lateral medulla is deficient rightward saccades (contralesional hypometric saccades), and over-active leftward saccades (ipsilesional hypermetric saccades), and ipsilesional ocular lateropulsion given this baseline imbalance. M...Image
49 A Comparison of Nystagmus and Saccadic Intrusions/OscillationsNystagmus can be classified into pendular and jerk waveforms, where both are generated by a slow, pathologic phase. Corrective phase (the position reset mechanism) differs. In pendular nystagmus, the eyes move back and forth with about the same velocity and amplitude, similar to that of a pendulum...Image
50 Sagittal Section of the Midbrain Showing Structures Related to Normal Eyelid Function𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: During a vertical saccade, the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) is activated, which excites the superior rectus (SR) and inferior oblique (IO) (IIIrd nerve) subnuclei. Additionall...Image
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