disorder of higher function

Infarction

An area of tissue death due to lack of oxygen.

Leading cause of infarction

Cerebrovascular disease, accounting for about 80% of infarctions.

Major causes of cerebral infarction (15%)

Cardiogenic embolism, Atrial fibrillation, Ischemic heart disease, Valvular heart disease, Infective endocarditis.

Major causes of cerebral infarction (5%)

Other causes: Dissections, Hypercoagulable states, Vasculitis, Systemic hypotension.

Anterior cerebral artery (ACA) supply

The medial surface of the frontal, parietal, and occipital lobes.

Largest branch of internal carotid artery

The middle cerebral artery (MCA).

MCA and Circle of Willis

No, the MCA is not part of the Circle of Willis.

Supply of the MCA

The anterior temporal lobes and the parietal and frontal lobes.

Basilar artery supply

The base of the cerebrum and most of the cerebellum through the vertebrobasilar distribution.

Structures supplied by basilar artery/posterior communicating artery

The occipital lobe, brainstem, optic radiations, and cerebellum.

Types of ischemic events

Transient ischemic attack (TIA), Reversible ischemic neurological deficit (RIND), Cerebral infarction.

Transient ischemic attack (TIA)

A rapid-onset, temporary reduction in perfusion causing a temporary focal neurological deficit with no remaining deficit.

Typical duration of a TIA

Usually 2–15 minutes, but it can last up to 24 hours.

Reversible ischemic neurological deficit (RIND)

Focal ischemia with improvement occurring over no more than 72 hours.

Cerebral infarction definition

A permanent disorder with fixed deficits that may be stable, improving, or progressing.

Hallmark findings of vertebrobasilar disease

Sudden hearing loss and vertigo lasting a few minutes associated with nausea/vomiting.

Cause of sudden hearing loss in vertebrobasilar disease

A small branch of the AICA supplies the inner ear, so ischemia can cause sudden hearing loss.

Beauty shop dolichoectasia

Vertebral artery dolichoectasia, characterized by elongation, distension, or tortuosity of the vertebral artery.

Typical visual disturbances in vertebrobasilar disease

Diplopia/oculomotor palsies, Blurry vision, Visual phenomena (tadpoles, snowflakes, sparklers, pinwheels), Transient achromatopsia, Visual field disturbances.

Triad of vertebrobasilar insufficiency

Dimming or blurry vision in both eyes, Headache, Dizziness.

Differentiating vertebrobasilar insufficiency from migraine

Consider age of onset, family history, previous episodes of migraine.

Four syndromes of vertebrobasilar disease

Subclavian steal syndrome, Midbrain syndromes, Pontine syndromes, Medullary syndromes.

Subclavian steal syndrome

Subclavian artery stenosis causing decreased pressure distal to the stenosis, diverting blood through the vertebral artery toward the arm, leading to transient cerebral ischemia.

Manifestation of subclavian steal syndrome

Typically manifests with ipsilateral arm exercise.

Symptoms of subclavian steal syndrome

Vertigo, Syncope, Dysarthria, Nystagmus, Diplopia, Visual field defects.

Top-of-the-Basilar syndrome

A midbrain/posterior circulation syndrome caused by infarction from posterior circulation emboli, dissection, or systemic hypotension.

Hallmark ocular signs of midbrain syndromes

Supranuclear CN III palsy, Vertical gaze palsy, Supranuclear vertical ophthalmoplegia.

Dorsal Midbrain (Parinaud's) Syndrome

Characterized by impaired upgaze, pupils with absent direct light response, light-near dissociation, bilateral lid retraction (Collier's sign), skew deviation, convergent misalignment, convergence-retraction nystagmus, possible CN IV palsy, preserved VOR.

Weber syndrome

A ventral midbrain syndrome causing ipsilateral CN III palsy (ptosis and mydriasis) and contralateral hemiparesis.

Benedikt syndrome

A ventral paramedian midbrain syndrome causing CN III palsy with ptosis and mydriasis, and contralateral hemi-tremor/ataxia.

Hallmark ocular signs of pontine syndromes

CN VI and CN VII palsy, Horizontal gaze palsy, Ocular bobbing.

Locked-in syndrome

A state where the patient is fully paralyzed but can communicate through blinking and eye movements.

Cause of impaired horizontal eye movement in locked-in syndrome

Due to CN VI involvement.

Internuclear ophthalmoplegia (INO)

A brainstem lesion affecting the medial longitudinal fasciculus (MLF) between CN III and CN VI.

Eye movement findings in INO

Ipsilateral adduction is impaired while abduction of the opposite eye is preserved, often with endpoint nystagmus.

Convergence in INO

Yes, convergence is preserved.

WEBINO

Wall-Eyed Bilateral Internuclear Ophthalmoplegia—bilateral INO causing impaired adduction of either eye, often with exotropia.

One-and-a-Half Syndrome

INO + ipsilateral gaze palsy, due to involvement of the MLF and PPRF.

Millard-Gubler syndrome

A ventral pontine syndrome characterized by CN VI palsy, CN VII palsy, and contralateral hemiparesis.

Foville syndrome

A lower dorsal pontine syndrome characterized by ipsilateral CN V, VII, and VIII palsies, Horner syndrome, and horizontal conjugate gaze palsy, associated with AICA occlusion.

Hallmark signs of medullary syndromes

Horner syndrome, Ipsilateral facial pain/temperature loss, Ipsilateral paralysis of the tongue, soft palate, and vocal cord.

Lateral medullary/Wallenberg syndrome

A lateral medullary stroke caused by PICA occlusion.

Important findings in Wallenberg syndrome

Reduced corneal/blink reflex, vertigo, nausea/vomiting, ocular lateropulsion, Horner syndrome, ipsilateral facial pain/temperature loss.

Artery associated with macular sparing in PCA occlusion

The posterior cerebral artery (PCA) supplies the occipital cortex; PCA occlusion can produce contralateral hemianopia with macular sparing.

Risk factors for hemorrhagic stroke

Hypertension, Smoking, Alcohol consumption, Pregnancy/straining, Drug abuse (especially cocaine), oral contraceptives/estrogen.

Presentation of ruptured aneurysm

Classically with 'the worst headache of my life', often accompanied by nausea/vomiting, neck pain/nuchal rigidity, photophobia, diplopia, and seizures.

Retinal ganglion cell types in visual perception

Parvocellular (midget), Magnocellular (parasol), Koniocellular (bistratified).

Function of parvocellular/midget ganglion cells

Small receptive fields, provide fine spatial resolution, and convey red-green color opponency.

Parvocellular system and motion detection

No, it is a static firing system and does not detect motion.

Clinical test for parvocellular system

Spatial contrast sensitivity.

Function of magnocellular/parasol ganglion cells

Large receptive fields, lower spatial resolution, and convey motion information.

Clinical test for magnocellular system

Frequency doubling technology (FDT), Motion automated perimetry.

Function of koniocellular/bistratified ganglion cells

Large receptive fields and convey blue-yellow color opponency.

Clinical test for koniocellular system

Short-wavelength automated perimetry (SWAP).

Two occipitofugal pathways

Dorsal occipitofugal pathway = 'Where?', Ventral occipitofugal pathway = 'What?'.

Responsibility of the dorsal occipitofugal pathway

Visuospatial analysis, Localization of objects in space, Guiding movement toward objects.

Pathway of the dorsal occipitofugal system

V1 → V2 → V3 → V5 → parietal/superior temporal cortex.

Lesions of the dorsal occipitofugal pathway effects

Hemispatial neglect, Balint syndrome: Simultanagnosia, Optic ataxia, Acquired oculomotor apraxia.

Parietal lesion causing neglect

An inferior parietal lesion.

Parietal lesion causing ataxia

A superior parietal lesion.

Simultanagnosia

Inability to integrate multiple elements of a scene into a global image, despite having no true visual field defect.

Optic ataxia

Visual input disconnected from the motor system, causing inaccurate reaching for objects as if blind.

Spasm of fixation

Loss of voluntary eye movement with persistent fixation on an object.

Lesion associated with spasm of fixation

The frontal eye fields.

Hemispatial neglect definition

Inability to attend to stimuli in one side of space; specifically, inability to attend to the left visual field.

Lesion causing left hemispatial neglect

Damage to the right hemisphere.

Visual allesthesia

Phenomenon in which the retinotopic visual field is rotated, flipped, or inverted.

Lesion locations for visual allesthesia

At the level of the medulla or posterior parietal cortex.

Function of ventral occipitofugal pathway

Processing of color, shape, pattern, object identification, object-based attention, visual identification, language, memory, emotion.

Pathway of ventral occipitofugal system

V1 → V2 → V4 → inferior temporal cortex, angular gyrus, and limbic structures.

Lesions of ventral occipitofugal pathway effects

Visual alexia, Anomia, Visual agnosia, Visual amnesia, Visual hypo-emotionality.

Visual-verbal disconnection definition

Usually associated with left occipital lobe infarctions, producing difficulty naming objects from sight.

Alexia without agraphia definition

Inability to read despite being able to write; associated with left occipital lobe infarction/visual-verbal disconnection.

Visual-visual disconnection definition

Bilateral damage to the occipito-temporal cortex, causing prosopagnosia and associative object agnosia.

Prosopagnosia

Loss of ability to identify previously familiar faces.

Associative object agnosia

Loss of object identification.

Visual-limbic disconnection definition

Damage to the occipito-temporal cortex causing visual amnesia and visual hypo-emotionality.

V1 location

The striate cortex.

V2 and V3 location

Surround the striate cortex.

V4 location and function

Ventromedial occipital lobe; involved in color vision.

V5 location and function

Lateral occipital lobe; involved in motion perception.

Anton syndrome definition

Bilateral striate cortex damage resulting in denial of blindness.

Blindsight definition

Unconscious, basic visual perception that persists in blind patients after acquired lesions to the visual cortex.

Riddoch phenomenon definition

Preservation of the perception of motion in a blind hemifield.

Importance of Riddoch phenomenon

Considered a good indicator for recovery after occipital stroke.

Type of ataxia with homonymous hemianopia from occipital lesions

Visual ataxia, with sensation of falling toward the blind hemifield.

Differentiation of visual ataxia from ataxia due to vestibular disease

In visual ataxia from an occipital lesion, vestibular responses are usually normal/intact.

Cerebral achromatopsia

Color vision loss caused by damage to the ventromedial occipital cortex.

Bilateral versus unilateral lesions causing cerebral achromatopsia

Bilateral lesions → complete achromatopsia; Unilateral lesions → hemi-achromatopsia.

Causes of acquired cerebral achromatopsia listed

Bilateral PCA infarction, Metastatic tumor, Posterior cortical dementia, Herpes simplex involving the ventromedial area, Seizure, Migraine, Vertebrobasilar insufficiency.

Lesion if form, texture, color vision is normal but motion cannot be detected

Area V5.

Akinetopsia definition

Loss of perception of visual motion despite preserved form, texture, and color vision.

Akinetopsia association

Sagittal sinus thrombosis.

Charles Bonnet syndrome definition

A release hallucination that frequently occurs in patients with bilateral visual loss.

Types of hallucinations in Charles Bonnet syndrome

Simple (flashes) and Complex (people or objects).

Psychiatric status of patients with Charles Bonnet syndrome

Patients are psychiatrically normal.

Prevalence of Charles Bonnet syndrome in blind patients

Approximately 11–13%.

Factors worsening Charles Bonnet syndrome

Social isolation.

Typical characteristics of visual migraines

Usually unformed visual hallucinations.

Differences between visual seizures and visual migraines

Visual seizures often lack a typical migraine history, may have atypical frequency/duration, and are associated with other seizure phenomena.