Cranial Nerve Palsies

CN III Palsy - The Droopy Director

• Causes:
  • Microvascular (DM, HTN): Pupil often spared.
  • Compressive (PCOM aneurysm, tumor): Pupil often involved. ⚠️
  • Trauma.
• Signs:
  • Ptosis (droopy eyelid).
  • Eye "down and out".
  • Mydriasis (dilated pupil; if parasympathetic fibers hit).
  • Diplopia.
• Pupil:
  • Sparing: Ischemia likely.
  • Involved: Urgent imaging (aneurysm?).

⭐ A pupil-involving CN III palsy suggests a compressive lesion like a PCOM aneurysm.

CN IV Palsy - The Tilted Viewer

• Etiology: Trauma (most common), congenital, vascular (DM, HTN), tumor, idiopathic.
• Clinical Features:
  • Vertical/torsional diplopia: worse on downgaze & contralateral gaze (e.g., reading, descending stairs).
  • Compensatory head tilt to the shoulder opposite the lesion.
• Examination:
  • Parks-Bielschowsky 3-step test to isolate paretic Superior Oblique (SO).
  • Affected eye shows hypertropia, worsening on adduction & ipsilateral head tilt.

⭐ Patients characteristically tilt their head AWAY from the side of the lesion (towards the contralateral shoulder) to minimize diplopia_._

CN VI Palsy - The Sideways Straggler

• Nerve: Abducens (CN VI). Muscle: Lateral Rectus (LR). Action: Abduction (outward eye movement).
• Symptoms:
  • Horizontal, uncrossed diplopia; worse on ipsilateral gaze & for distance.
  • Esotropia (eye turns inward), more pronounced on attempted abduction.
  • Compensatory head turn towards the side of palsy to maintain binocular vision.
• Common Causes:
  • Microvascular (diabetes, hypertension) in older adults (>50 yrs).
  • Trauma.
  • ↑ Intracranial Pressure (ICP).
  • Tumors (e.g., pontine glioma, nasopharyngeal carcinoma), inflammation.

⭐ Sixth nerve palsy can be a "false localizing sign," indicating raised intracranial pressure (ICP) due to its long, vulnerable intracranial course over the petrous apex, rather than a direct lesion of the nerve nucleus or fascicle at that specific ICP-related site of injury (e.g., Dorello's canal).

Combined Palsies - The Cranial Crowd

• Multiple CN palsies localize lesion.
• Cavernous Sinus Syndrome:
  • III, IV, V1, V2, VI, sympathetics.
  • Proptosis, ophthalmoplegia, facial sensory loss (V1/V2).
  • Causes: Tumor, fistula, inflammation.
• Superior Orbital Fissure (SOF) Syndrome:
  • III, IV, V1, VI. (V2 spared vs. Cavernous Sinus)
• Orbital Apex Syndrome:
  • SOF nerves + II (optic neuropathy → ↓vision).
  • E.g., Tolosa-Hunt (painful ophthalmoplegia, steroid-responsive).
• Gradenigo's Syndrome:
  • VI palsy, V pain (V1/V2), petrous apicitis.

⭐ Tolosa-Hunt syndrome: painful ophthalmoplegia from granulomatous inflammation (cavernous sinus/SOF), responds to steroids.

Cranial Nerve Palsy Workup - The Neuro-Op Toolkit

• History: Onset (sudden/gradual), progression, trauma, pain, diplopia, ptosis, associated neurological/systemic symptoms.
• Examination:
  • Visual Acuity, Visual Fields, Pupils (RAPD, size, reactivity).
  • Ocular Motility (versions, ductions), Cover tests, Lid position.
  • Fundoscopy (optic disc), Exophthalmometry.
  • Complete neurological & relevant systemic exam.
• Investigations (Clinical-Guided):
  • Bloods: CBC, ESR/CRP, Glucose/HbA1c, TFTs, AChR-Ab.
  • Imaging: MRI (brain/orbits) ± MRA/MRV; CT (trauma).
  • LP (infection/inflammation).
  • Tensilon/Ice pack test (Myasthenia).

⭐ In an isolated CN III palsy, pupillary involvement (mydriasis) is a red flag for a compressive lesion (e.g., PCOM aneurysm) until proven otherwise; pupillary sparing often points to microvascular ischemia (e.g., diabetes, hypertension).

High‑Yield Points - ⚡ Biggest Takeaways

• CN III palsy: Ptosis, mydriasis, "down and out" eye. Pupil involved = compressive (aneurysm); pupil spared = ischemic.
• CN IV palsy: Vertical diplopia, worse on contralateral gaze & ipsilateral head tilt. Head tilt away from lesion.
• CN VI palsy: Horizontal diplopia, worse on ipsilateral gaze (abduction failure). Vulnerable to ↑ICP.
• Painful ophthalmoplegia: Suspect PCOM aneurysm, Tolosa-Hunt, or GCA.
• Aberrant regeneration CN III: Lid-gaze dyskinesis after compressive injury, not ischemic.
• Multiple palsies: Think cavernous sinus, orbital apex, or brainstem.