Diplopia Impaired Ocular Movement

CAUSES OF IV and VI NERVE LESIONS Midbrain

When IV nerve lesion is associated with:

Orbital fissure orbit

Cavernous sinus

Causes as for III

nerve lesion contralateral hemiparesis, contralateral hemisensory loss

Proximity to anterior medullary velum and superior vermis

Superior and inferior colliculi

Posterior cerebral and superior \1 cerebellar arteries „'TV

Cerebellar peduncles

(Tentorium cerebelli and cerebellum omitted)

intrinsic midbrain lesion s

cerebellar tumour, " e.g. medul- j loblastoma i infarction, demyelination, intrinsic tumour, e.g. glioma

infarction, demyelination, intrinsic tumour, e.g. glioma contralateral hemiparesis, contralateral hemisensory loss

Orbital fissure 1 Causes orbit > as for

Cavernous sinus nerve lesion

Long intracranial course may result in damage from raised intracranial pressure (false localising sign)

Orbital fissure 1 Causes orbit > as for

Cavernous sinus nerve lesion

Petrous Bone

When VI nerve lesion is associated with: PAIN in the distribution of -] pefros,f/s _ trigeminal nerve (especially I Gradenig0's the first division) syndrome

Excessive LACRIMATION - J superior petrosal sinus involvement.

Lower pons

Long intracranial course may result in damage from raised intracranial pressure (false localising sign)

When VI nerve lesion is associated with:

contralateral hemiparesis, 1 nuclear or 1 infarction, contralateral hemisensory loss, L intramedullary I demyelination, lower motor neuron vn lesion lesion intrinsic tumour, e.g. glioma

NOTE: Infective or carcinomatous meningitis and nerve trunk infarction may also involve the IV and VI nerves, although less often than the III nerve.

Investigative approach

Impaired ocular movement from III, IV or VI nerve lesions requires full investigation with conventional or dynamic CT scan, MRI and, where appropriate, CSF cytology. Unexplained III nerve lesions require angiography, only in elderly hypertensive or diabetic patients with pupillary sparing may angiography be omitted.

When myopathy or myasthenia gravis is suspected then appropriate investigations -acetyl choline receptor antibodies, EMG studies and occasionally muscle biopsy - may be necessary.

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