Cranial Nerve (Clinical Notes)

 Cranial Nerves

As we already know, cranial nerves consist of 12 nerves. These nerves originate from the different parts of the brain, mainly from the brainstem. Cranial nerves supply different parts of the body and any kind of damage to these nerves may cause a medical anomaly. Some of the clinical conditions that can occur to these nerves are described below;

FOR NOTES OF CRANIAL NERVES : CRANIAL NERVES

Olfactory Nerve

 Inability of the nose to sense any smell is known as Anosmia. It may be unilateral or bilateral.

Causes

Unilateral Anosmia

• Damage to olfactory mucous, nerve or tract
• Olfactory Cortex lesion
• Fracture of Ethmoid bone (Ant Cranial fossa)
• Frontal lobe lesions (As they can press the nerve below them)

Bilateral Anosmia

• Common Cold
• Allergic Rhinitis (Diseases of the olfactory mucous membrane)

Optic Nerve

Optic nerve mainly makes us able to see. The optic pathway may be damaged at different spots that creates a wide range of effects that can be observed.

Circumferential Blindness

The blindness in which the eye does not see the outer circumference area of the visual field.

It may be caused by;

• Hysteria
• Optic Neuritis
• Spread of infection from Sphenoid/ Ethmoid sinuses

Total Blindness of One Eye

This condition happens when one of the eyes completely loses its visual field.

Common causes include;

• Damage to the Optic Nerve

Binasal Hemianopia

When the eyes lose their central visual fields. It is known as Binasal Hemianopia.

• Lesions of the lateral Optic chiasma 
• If unilateral damage occurs then Nasal Hemianopia is caused 

Bitemporal Hemianopia

In this condition, the eyes lose their peripheral visual fields. The most common cause is the damage to central area of the Optic chiasma mainly due to any tumor of Pituitary gland.

Contralateral Homonymous Hemianopia

In this disease, the person may lose his/her visual field in a particular area of both the eyes. He may be losing right sides of both the visual fields or left part.

Causes include

• Damage to Optic tract
• Optic Radiation or Visual Cortex damage

Occulomotor Nerve

All the extra occular muscles except for the Lateral rectus and Superior Oblique are supplied by CN-III. Damage to Occulomotor nerve may cause;

• External Strabismus (Eye looks laterally)
• Ptosis (Dropping of eyelids)
• Pupil widely dilated
• Pupil non reactive to light

Incomplete Lesions

Internal Ophthalmoplegia

• The sphincter and ciliary muscles are affected while the extraoccular muscles are spared.

External Ophthalmoplegia

• Extraoccular muscles are affected while the intrinsic muscles retain their integrity.

Trochlear Nerve

This nerve innervates the superior oblique and moves the eye laterally as well as inferiorly.

Patient complains of diplopia while looking straight downwards.

Causes may be;

• Head Injury
• Bruising/ Stretching of Nerve
• Cavernous sinus thrombosis
• Internal Carotid Artery aneurysm
• Lesions of Midbrain

Trigeminal Nerve

Trigeminal nerve contains a sensory as well as motor part. Damage to the nerve may cause Trigeminal Neuralgia.

Trigeminal Neuralgia

The areas of V2 and V3 divisions of the trigeminal nerve are mainly affected and a severe stabbing pain over the face is caused. Ophthalmic division is rarely damaged.

Abducens Nerve

Abducens nerve supplies the lateral rectus muscle. The patient cannot deviate his eye laterally. And the medial rectus pulls the eye medially.

• Internal Strabismus
• Diplopia

These may be caused by damage to cavernous sinus, internal carotid artery, or by the lesions of Pons 

Facial Nerve

The wide array of the path of the facial nerve causes too many sites that can be damaged. The structures that pass close to the facial nerve may help us localize the lesions. Some of the lesions and their effects are listed below;

• CN-VII + CN-VI dysfunction (Lesion in pons)
• CN-VII + CN-VIII dysfunction (Lesion in Internal Acoustic meatus)
• Sensitivity to sound (Lesion of nerve to stapedius)
• Loss of taste over Anterior 2/3 of tongue (lesion of Chorda tympani)
• Swelling of Parotid Gland (Parotid Gland cancer with damage to the terminal nerves in it)

Upper Motor Neuron Lesion

As the part of facial nuclei that control the upper part of face get Corticonuclear fibers from both the cerebral hemispheres. Thus this part is not affected in unilateral lesions.

Lower Motor Neuron Lesion

In case of lower motor neurons, all the muscles will get paralyzed.

Bell's Palsy

A dysfunction of facial nerve when it is in the facial canal. The actual cause of Bell's palsy is still unknown. As the facial nerve gives off many nerves inside the facial canal, many variations may be caused. This results in temporary loss of function, that causes a lower motor neuron type of facial paralysis.

Vestibulocochlear Nerve

This nerve contains two parts and both parts can be damaged;

Vestibular Nerve

Damage to vestibular nerve may cause;

• Nystagmus (Uncontrollable rhythmic oscillation of eyes)

                 Due to disturbance in the reflexive control of MLF that connects 3,4 and 6 nerve to vestibular nerve.

• Vertigo (dizziness)

                 Due to lesions of the vestibular nuclei, cerebellum or multiple sclerosis, tumors and lesions of brainstem.

Cochlear Nerve

Deafness and tinnitus are mainly caused by disturbance of the cochlear nerve.

Lesions of internal ear, cochlear nerve or the CNS mainly cause disturbances;

Internal Ear Lesions

• Meniere disease
• Acute labyrinthitis
• Trauma (head injury)

Cochlear Nerve Lesions

• Acoustic Neuroma (tumor)
• Trauma

CNS Lesions

• Multiple sclerosis
• Tumors of mid brain

Glossopharyngeal Nerve

Isolated lesion of the glossopharyngeal nerve are very rare and if they occur, they also involve the vagus nerve. 

Vagus Nerve

Gag Reflex is mainly controlled by the Glossopharyngeal as well as the vagus nerves. In patients with unilateral lesion of the vagus nerve, there is very little or no Gag reflex on that side.

Besides this many other conditions are related to Vagus nerve;

• Hoarseness or absence of voice (Vagal Nerve palsy)
• Short term bp regulation compromised
• Affected parasympathetic innervation to the heart and other vital organs.
• Paralysis of cricothyroid muscles.

Accessory Nerve

Damage to the Accessory nerve mainly causes the following;

• Paralysis of the SCM and the Trapezius
• SCM atrophy causes the head to tilt to the other side.
• Trapezius atrophy causes the shoulder to drop and it is very difficult to abduct the arm.

Main causes of damage maybe any type of damage to the spinal root of the Accessory nerve by stab, gunshot or any other threatening material. 

Hypoglossal Nerve

Hypoglossal Nerve damage may cause the abnormality of the intrinsic as well as the extrinsic muscles of the tongue. This in turn affects the shape and the movement of the tongue in the following ways;

• The tongue deviates towards the side of lesion when it is asked to put out. (LMNL)
• Tongue appears small on the side of the lesion (muscle atrophy)
• If the tongue deviated to the side opposite to the lesion (UMNL/ Corticonuclear fiber damage)

Prepared By 

Muhammad Qamar Shahid

Batch 12

IPMR KMU