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n_exam_cranialn

Cranial nerve examination

see also:

NB. Myasthenia gravis has the ability to mimic virtually any cranial neuropathy, including isolated third nerve palsies and INO. Myasthenia gravis must remain a possible diagnosis when encountering a third nerve palsy, especially when the course is variable or atypical.

Olfactory nerve:

  • test esp. if personality change (frontal lobe lesion) or unexplained visual loss (optic chiasm lesion)

Optic nerve:

visual acuity (central vision):

  • Snellen chart at 6m or Rosenbaum pocket card at 1foot
  • with corrective glasses otherwise use pinhole if glasses unavailable

gross visual fields (peripheral vision)

  • divide field into 4 quadrants (inf, sup, nasal & temporal) - check each eye individually

ophthalmoscopic examination for retinal & optic N pathology, papilloedema

CIII, IV & VI:

extra-ocular movements

  • hold pen or finger in front of pt, ask pt to follow it while you move it horizontally.
  • ask pt how many pens he sees - if “two” is it monocular or binocular & note position - see diplopia
  • hold pen horizontally & move it vertically
internuclear ophthalmoplegia
  • due to lesion of ipsilateral medial longitudinal fasciculus which normally allows conjugate eye movement by connecting the paramedian pontine reticular formation (PPRF) -abducens nucleus complex of one side to the oculomotor nucleus of the opposite side.
  • failure of an eye to adduct on gaze to opposite side
  • results in horizontal diplopia & may cause compensatory nystagmus in the partner eye.
  • bilateral lesions in age < 50yrs is almost always due to multiple sclerosis (MS)
  • unilateral lesions may also be due to brainstem infarct, brainstem/fourth ventricle tumour, viral infection, trauma, drugs, subdural haematoma, etc.
  • myasthenia gravis may mimic INO.
  • see revoptom.com for more details.

check for nystagmus:

  • marked nystagmus on lateral gaze or any on forward gaze is abnormal
  • vertical nystagmus ⇒ brain stem lesion or phencyclidine
  • pendular ⇒ usually congenital

CIII lesion:

  • complete ptosis, inability to adduct eye & fixed, dilated pupil
aetiology:
  • brainstem lesions:
    • brainstem infarct - usually also involves pyramidal & cerebellar pathways ⇒ c/lat. hemiplegia & ipsilat. cerebellar ataxia
    • metastatic disease
  • within subarachnoid space (usually produces painful, isolated CIII lesions +/- pupil involvement)
    • post. commun. artery aneurysm or basilar aneurysm - often assoc. with ipsilat. periorbital pain.
      • suspect if either:
        • adult patient of any age presents with a complete or incomplete isolated third nerve palsy with pupillary involvement
        • 15-50yrs age and has a non-pupillary involved isolated third nerve palsy
      • CT or MR angiography ASAP as risk of aneurysm rupture
    • ischaemic neuropathy (eg. vasculopathy)
  • aneurysms within cavernous sinus - usually also involve CIV, CV, CVI nerves
  • with normal pupil and aged > 55yrs with sudden onset ⇒ isolated CIII lesion due to atherosclerosis, hypertension or diabetes mellitus.
  • other causes: tumour, basal meningitis (eg. TB), head injury, toxins (eg. snakebite).
  • children < 14yrs are most likely traumatic or congenital.

CIV lesion:

  • failure to adduct eye downwards
aetiology of isolated lesion:
  • head injury, ischaemia due to atherosclerosis or diabetes; tumour.

CVI lesion:

  • failure to abduct the eye.
aetiology:
  • congenital - Duane syndrome
  • vascular - brainstem infarction - usually also ipsil. facial palsy & c/lat. hemiparesis.
  • cavernous sinus pathology - usually also involves CIII, CIV, CV nerves
  • tumour, infection spreading from otitis media, TB meningitis, MS, # base of skull, raised intracranial pressure (ICP).

pupillary responses:

  • if pupil constricts to light, testing for accommodation adds no further information as pupillary reaction to accommodation but not light is rare, seen only in tertiary syphilis
  • pupillary size in room light
  • unequal pupils may be normal (anisocoria)
unilaterally dilated pupil:
  • if with abnormal GCS suggests uncal herniation
  • consider CIII lesion, eye drops
  • Holmes-Adie pupil (slowly constricts with accommodation)
unilaterally small pupil
  • Horner's syndrome, eye drops.
bilaterally dilated pupils
  • suggests prolonged anoxia, anticholinergics or sympathomimetics
bilaterally constricted pupils
  • suggests narcotics, organophosphates or pontine haemorrhage (also Argyll Robertson pupils of tertiary syphilis)

Trigeminal nerve (V):

  • a CNS lesion affecting CV is likely to involve all 3 divisions, thus it is not necessary to test them individually.
  • test sensory function by simultaneously pressing sharp object on both cheeks & asked if can feel them as sharp.
  • test motor function by asking pt to clench teeth while you palpate masseter muscle tone.

Facial nerve (CVII):

  • weakness is usually apparent to the patient and not an unexpected finding.
  • in subtle cases, weakness is often apparent by:
  • evidence of flattening of nasolabial fold
  • ask pt to show his teeth, whistle & puff (in succession) - smiling itself is not adequate!
  • cortical motor fibres to the forehead muscles run from both motor cortices to each CVII nucleus & thus a cortical “central” lesion does not produce paralysis of forehead muscles whereas a peripheral lesion involves the whole ipsilateral face.
  • CVII has two main divisions:
  • motor root to ipsilateral facial muscles including forehead, and via nerve to stapedius, the stapedius muscle in the ear (lesion results in hyperaccusis)
  • nervus intermedius:
    • fibres pass through geniculate ganglion
    • supplies taste to ant. 2/3rds tongue via chorda tympani
    • supplies autonomic fibers via:
      • the major superficial petrosal nerve via pterygopalatine ganglion which innervate the nasal, palatine and lacrimal glands.
      • the lingual nerve via teh submandibular ganglion which supplies the sublingual and submandibular salivary glands.
  • if the lesion occurs at the level of the nucleus in the brain stem, it usually also involves:
  • CVI as the CVII fibers loop around the CVI nucleus before exiting the pons.
  • long motor tract fibres
  • Ramsay-Hunt syndrome:
  • peripheral CVII palsy + herpetic vesicles in ear canal and on tympanic membrane +/- vertigo/tinnitus

Acoustic nerve (CVIII):

  • hearing can be rapidly screened by :
    • rub finger/thumb of each hand next to each ear, alternating which hand rubs, ask which is heard.
  • if defect, ask patient to hum. In sensorineural defect, humming is heard loudest in normal ear.
  • vestibular nerve is generally not tested unless pt is complaining of vertigo or dizziness:
    • Nylen-Barany manouvre

Glossopharyngeal N (CIX) and Vagus nerve (CX):

  • these are tested together:
    • lightly depress tongue, gag reflex should cause soft palate to retract symmetrically.
  • if nerve injury is one sided, palate will retract to normal side.
  • compromise of these nerves is extremely rare.

Accessory nerve (CXI):

  • occasionally damaged during neck injuries
  • test trapezius by shrugging shoulders, if equivocal, test sternocleidomastoid contraction.

Hypoglossal nerve (CXII):

  • ask pt to stick out his tongue, if there is weakness, tongue will deviate to side of lesion.
  • see also bulbar palsy
n_exam_cranialn.txt · Last modified: 2016/03/17 20:36 by gary1