Cranial Nerve Lesions: Comprehensive Summary
| CN | Lesion Presentation | High-Yield Clinical Pearl |
|---|---|---|
| I | Anosmia | Common in frontal lobe masses/trauma. |
| II | Vision loss, pupillary defect | Check for RAPD (Marcus Gunn pupil). |
| III | “Down and out”, ptosis, dilated pupil | Compressive (e.g., PCom aneurysm) affects the pupil. |
| IV | Vertical diplopia, head tilt away | Patient compensates by tilting the head to the unaffected side. |
| V | Facial sensory loss, jaw deviation | Jaw deviates toward the side of the lesion. |
| VI | Medial strabismus, horizontal diplopia | Lateral rectus palsy is most susceptible to increased ICP. |
| VII | Facial palsy (LMN vs UMN) | UMN spares the forehead; LMN affects the entire face. |
| VIII | Hearing loss, vertigo, tinnitus | Check for vestibular schwannoma (acoustic neuroma). |
| IX | Dysphagia, loss of gag reflex | Often affected with CN X in jugular foramen lesions. |
| X | Uvula deviation (away from the lesion) | Vagus nerve damage causes dysphonia and dysphagia. |
| XI | Shoulder drop, neck weakness | Weakness in the trapezius and SCM muscles. |
| XII | Tongue deviation (toward lesion) | LMN lesion; tongue “licks the wound.” |
High-Yield Distinction:
UMN vs. LMN (Facial Nerve): A central (UMN) lesion spares the forehead due to bilateral cortical innervation; a peripheral (LMN/Bell’s Palsy) lesion affects the entire side of the face.