Скачать или смотреть Cranial nerve lesions, part 1 (olfactory & optic nerves)

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This document summarizes lesions and clinical examination techniques for the Olfactory (CN I) and Optic (CN II) cranial nerves.

Olfactory Nerve (CN I)
Anatomy: Unmyelinated filaments pass through the cribriform plate to the olfactory bulb; it is a direct extension of the CNS.
Lesion: Anosmia.
Pathology: Common causes of anosmia include trauma (shearing of filaments in cribriform plate fractures) or viral infection.
Clinical Exam: Test each nostril separately with non-irritating odors such as coffee or soap, and avoid ammonia, which triggers CN V pain fibers.
Clinical Highlight: Foster Kennedy Syndrome (due to an olfactory groove tumor like a meningioma) is a triad of ipsilateral anosmia, ipsilateral optic atrophy, and contralateral papilledema.
Optic Nerve (CN II) Examination

The CN II exam is divided into four components:
Acuity: Measured with a Snellen chart; establishes baseline vision sharpness and targets the macula integrity.
Fields: Assessed via confrontation testing to map the visual field and localize a lesion.
Neuro-Ophthalmology Golden Rule: The left side of the brain sees the right side of the world, and vice versa.
Lesion Signatures: Specific field defects localize a lesion along the visual pathway.
Optic Nerve: Monocular Blindness.
Optic Chiasm: Bitemporal Hemianopsia (e.g., Pituitary Adenoma).
Optic Tract: Contralateral Homonymous Hemianopsia.
Optic Radiations (Meyer's Loop in Temporal Lobe): Contralateral Superior Quadrantanopia ("Pie in the Sky").
Optic Radiations (Parietal Lobe): Contralateral Inferior Quadrantanopia ("Pie on the Floor").
Visual Cortex: Contralateral Homonymous Hemianopsia with Macular Sparing (e.g., PCA stroke).
Reflexes (Light Reflex): The afferent limb is CN II, and the efferent limb is CN III. The Relative Afferent Pupillary Defect (RAPD), or Marcus Gunn pupil, is a sign of afferent pathway dysfunction.
Test: The Swinging-Flashlight Test reveals paradoxical dilation when light is swung to the affected eye.
Etiology: RAPD indicates unilateral/asymmetric optic nerve pathology, such as optic neuritis (associated with MS), ischemic optic neuropathy, or compressive optic neuropathy.
Differential: RAPD is distinguished from Anisocoria (efferent defect) because the pupils are typically equal at rest.
Fundoscopy: Direct visualization of the fundus for:
Papilledema: Swelling of the optic disc, indicating intracranial hypertension.
Optic Atrophy: Pale optic disc, indicating dead nerve fibers (e.g., advanced MS or long-term compression).