Hello :)
Before starting with the III nerve, Let us understand the term.
According to TABER'S medical dictionary, We need to understand 3 main type of palsy here.
1.NUCLEAR palsy :- Paralysis caused by lesion of the nuclei in CNS.
2.OCULAR palsy :- Paralysis of extraocular nd intraocular muscles.
3.MUSCULAR palsy :- Loss of the capacity of muscle to contract. It may be due to structural or functional disorders
-in the muscle at the myoneural junction,
-in efferent nerve fibres,
-in the cell bodies of nuclei of origin of the brain or of the gray matter of the spinal cord,
-in conducting pathways of the brain or spinal cord,
-in motor centres of the brain.
Third cranial nerve supplies
1. EXTRAOCULAR MUSCLES
-Superior rectus
-Inferior oblique
-Medial rectus
-Inferior rectus
2.INTRAOCULAR MUSCLES
-Levator palpebral superioris
-Ciliary body
-Iris sphincter msucle
THE LOCALIZATION OF THIRD NERVE LESION
-Supranuclear
-Nuclear
-Fascicular
-Basilar
-Intra-Cavernous sinus
-Superior orbital fissure
-Intra Orbital part
CLINICAL FEATURES OF THIRD NERVE PALSY:-
1. Ptosis - paralysis of LPS muscle.
2. Deviation – out, down and intorted (unopposed action of LR and SO).
3. Ocular movements:
• Adduction – MR
• Elevation – SR and IO
• Depression – IR
• Extorsion – IR and IO
4. Pupil is fixed and dilated – paralysis of sphincter pupillae muscle.
5. Accommodation is completely lost – paralysis of ciliary muscle.
6. Crossed diplopia – paralytic divergent squint.
7. Head posture – If the pupillary area is uncovered, head takes a posture consistent with the directions of actions of the paralysed muscles, i.e., head is turned on the opposite side, tilted towards the same side and chin is slightly raised. (Pathways between vestibular nuclei and oculomotor nuclei. These are Intranuclear pathway.)
FEATURES AND CAUSES OF THIRD NERVE LESIONS AT VARIOUS LEVELS
1. Supranuclear lesions
• Lesions of the cerebral cortex and supranuclear pathway produce conjugate paresis which affect both eyes equally.
• In supranuclear lesions although position and movements of the eyes are abnormal, they maintain their relative co-ordination and produce no diplopia.
2. Nuclear lesions
• Lesions involving purely the third nerve nucleus are relatively uncommon.
• Common causes include ; vascular diseases, demyelination, primary tumors and metastasis
• Lesions involving entire nucleus cause
-
an ipsilateral third nerve palsy with ipsilateral sparing and
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contralateral weakness of elevation.
• Lesions involving paired medial rectus subnuclei (ventromedial nucleus) cause a wall-eyed bilateral internuclear ophthalmoplegia ( WEBINO ) characterised by defective convergence and adduction.
3. Fascicular lesions
• Causes are similar to nuclear lesions.
-Benedikt syndrome involves the fasciculus as it passes through the red nucleus and is characterised by ipsilateral 3rd nerve palsy and contralateral extrapyramidal signs such as hemitremor.
-Weber syndrome involves the fasciculus as it passes through the cerebral peduncle and is characterised by ipsilateral 3rd nerve palsy and contralateral hemiparesis.
-Nothangel syndrome involves the fasciculus and the superior cerebellar peduncle and is characterised by ipsilateral 3rd nerve palsy and cerebellar ataxia.
-Claude syndrome is a combination of Benedikt and Nothangel syndromes.
4. Lesions involving basilar part of the nerve
• As the nerve runs in the subarachnoid space at the base of skull unaccompanied by any other cranial nerve, isolated third nerve palsies are frequently basilar.
• Causes :
1. Aneurysms at the posterior communicating artery cause isolated third nerve palsy with involvement of pupil.
2. Extradural hematomas which may cause tentorial pressure cone with downward herniation of the temporal lobe. This compresses the third nerve as it passes over the tentorial edge. Initially there occurs fixed, dilated pupil, which is followed by a total third nerve palsy.
3. Diabetes causes isolated 3rd nerve palsy with sparing of the pupillary reflexes.
5. Lesions involving intracavernous part of the nerve
• Because of its close proximity to other cranial nerves, intracavernous 3rd nerve palsies are usually associated with involvement of the 4th and 6th nerves, and the 1st division of trigeminal nerve.
-PULSATILE EXOPHTHALMOS can also be seen.
• In intracavernous 3rd nerve palsy, pupil is spared. Sometimes, pupil may be constricted owing to inv of sympathetics.
• Causes :
1. Diabetes may cause vascular palsy.
2. Pituitary apoplexy – may cause a third nerve palsy as a result of hemorrhagic infarction of a pituitary adenoma (after child birth), with lateral extension into cavernous sinus.
3. Intracavernous lesions – aneurysms, meningiomas, carotid-cavernous fistulae and Tolosa-Hunt syndrome (granulomatous inflammation).
6. Lesions of the intraorbital part of the nerve
• May cause isolated extraocular muscle palsies or may involve either superior division or inferior division or both.
• Causes : orbital tumors, pseudotumors, trauma and vascular diseases.
7. Lesions of pupillomotor fibres
• B/w the brainstem and the cavernous sinus, pupillomotor fibres are located superficially in the superior median quadrant of the nerve.
• They derive the blood supply from the pial blood vessels whereas the main trunk of the 3rd nerve is supplied by vasa nervorum.
I want to thank my teacher for such a beautiful explanation.
I hope it helped.
Do read about the following . (though I will write on this topic also)
1.Injury of Paramedian pontine reticular formation
2. Ptosis in Horner's syndrome and oculomotor nerve palsy.
-Upasana Y. :)
