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1 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
2 A flowchart approach to nystagmus/intrusionsIn tandem with the flowchart, the following added clues should be used to help with etiology: i) vector [horizontal, vertical, torsional]; ii) binocular or monocular; iii) spontaneous or provoked [e.g., BPPV]; iv) change with monocular viewing or gaze direction; v) rest of history, neurologic, and o...Image
3 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
4 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
5 Brainstem Ocular Motor MachinerySeen here is a sagittal view of the brainstem. The medulla has a significant role in gaze-holding, and the nucleus prepositus hypoglossi (NPH, along with the medial vestibular nucleus ) is the horizontal neural integrator. The abducens (6th) nucleus is located in the dorsal pons, and sends off the 6...Image/MovingImage
6 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
7 Central Anatomy of the Fourth NerveThe IVth or trochlear nucleus is located ventral to the central periaqueductal grey matter, dorsal to the medial longitudinal fasciculus (MLF) and medial to the oculosympathetic tract at the level of the inferior colliculus. The fascicles of the IVth nerve travel dorsally and caudally around the cen...Image
8 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
9 Coronal Section of the Brainstem Showing Ocular Motor Nuclei and Anatomy of the Vestibular Nucleus (with SCC Inputs)(A) Seen here is a coronal view of the brainstem showing the locations of the ocular motor nuclei (IIIrd, IVth, VIth) as well as the nuclei of VII and VIII (vestibular and cochlear). The vestibular nucleus (VN) is divided into the inferior, lateral, medial, and superior subnuclei, and the medial ves...Image
10 Eyelid AnatomySeen here are the major muscles of eyelid opening and closure. The levator palpebrae, which is innervated by the oculomotor nerve, inserts on the tarsus via the levator aponeurosis and directly on the skin of the upper eyelid. The superior tarsal muscle (also known as Muller's muscle, which is inner...Image
11 Figure 17: Bony Structures Relevant to the OrbitThe frontal, sphenoid, maxillary, ethmoid, and lacrimal bones make up the orbit. Structures passing through the optic canal include the optic nerve, oculosympathetic tract and ophthalmic artery. Structures passing through the superior orbital fissure include the superior ophthalmic vein, cranial ner...Image
12 Figure 1: Oculosympathetic Pathway for Pupillary DilationThe oculosympathetic tract is an uncrossed pathway that begins in the hypothalamus, with fibers descending in the brainstem (1st order, commonly affected in a lateral medullary syndrome), synapsing in the lower cervical/upper thoracic spinal cord (interomediolateral cell columns of C8-T2, also refer...Image
13 Figure 24: Typical Visual Field Defects Associated with Discrete Lesions Along the Visual PathwaysSpecific monocular or binocular visual field defects can be highly localizing when the neuroanatomy of the visual pathways is understood. The temporal visual field corresponds to the nasal retina, while the nasal visual field corresponds to the temporal retina. 1) Left optic nerve lesion - while an ...Image
14 Figure 27: Vascular Supply of the Optic Nerve Head, Choroid and RetinaThe ophthalmic artery is a branch of the internal carotid artery, which in turn, supplies the posterior ciliary (to choroid and outer retina) and central retinal (to inner retina) arteries. The central retinal artery (CRA) enters the optic nerve about 1 cm posterior to the globe, and an embolus may ...Image
15 Figure 2: Parasympathetic Pathway for Pupillary ConstrictionA bright light is shone in one eye, light enters the pupil and hyperpolarizes retinal photoreceptors which activates retinal ganglion cells. These signals propagate along the optic nerves, chiasm, optic tracts, and fibers responsible for the light reflex then synapse in the dorsal midbrain (prior to...Image
16 Figure 43: How the Brain Makes Sense of What It Sees - The Dorsal and Ventral Visual Pathways, and a 3 Tiered Approach to Vision1) Ventral ("what") stream - this begins with the ‘P' retinal ganglion cells à parvocellular layers of the lateral geniculate nucleus (LGN, 3-6) à V1/striate cortex (in blue) à V4/V4a (fusiform and lingual gyri) à occipitotemporal regions. 2) Dorsal ("where") stream - this begins with the ‘M...Image
17 Figure 46: The Course of the 6th (VI) NerveThe sixth nucleus is located dorsally, adjacent to the 4th ventricle, in the lower pons. The genu of the facial (7th) nerve wraps around the 6th nucleus, creating the facial colliculus, which bulges into the 4th ventricle. After the 6th nerve leaves the pons, it follows a vertical course along the c...Image
18 Figure 50: Anatomy and Physiology of the Saccadic PathwaysWhen a saccade is desired (or reflexively triggered), signals project from the saccade-related cortical eye fields to the superior colliculus, which serves to integrate and relay commands to the saccade generating brainstem circuitry. The inferior cerebellar peduncle (ICP) carries climbing fibers to...Image
19 Figure 51: Lateral Medullary Lesion Causing Saccadic DysmetriaA lesion of the left lateral medulla and inferior cerebellar peduncle (ICP) will cause decreased climbing fiber inhibition of the left dorsal vermis causing simple-spike (inhibitory) discharge of Purkinje cells to increase. Increased Purkinje cell firing leads to increased inhibition of the ipsilate...Image
20 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)Image
21 Figure 51: Lateral Medullary Lesion Causing Saccadic Dysmetria (Supplement)Image
22 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) SyndromeThis axial section of the medulla highlights those structures that, when damaged, are responsible for the vestibular and ocular motor features of the Wallenberg syndrome. The nucleus prepositus hypoglossi (NPH) and medial vestibular nucleus (MVN) complex is important for horizontal gaze-holding (neu...Image
23 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)Image
24 Figure 53: Vascular Distribution and Anatomy Relevant to the Lateral Medullary (Wallenberg) Syndrome (Supplement)Image
25 Figure 61: Vascular Distribution and Anatomy (Including 6th, 7th, 8th Nerves, MLF) of the PonsIn this axial section of the pons, the proximity of the 7th (VII) and 8th (VIII) fascicles can be appreciated, and a lateral inferior pontine syndrome (anterior inferior cerebellar artery, AICA territory), which could involve both of these fascicles, could cause acute prolonged vertigo accompanied b...Image
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