5th Cranial Nerve (Trigeminal Nerve)
Dr D V Siva Kumar
Asso Professor
Gen Medicine
Anatomy of the Trigeminal Nerve

5th Nerve subserves facial sensation and
innervates muscles of mastication
Anatomy :

Trigeminal central connections are complex
Anatomy of the Trigeminal Nerve
Dissociated sensory loss :

Def : loss of pain and temperature sensation with
preservation of light touch

The separate location of the main sensory nucleus and
nucleus of the descending trigeminal tract account for
dissociated sensory loss i.e., a low pontine or medullary
lesion will result in this loss

Low pontine medullary and cervical lesions produce a
characteristic ‘onion skin’ distribution of pinprick and
temperature loss. An ascending lesion spares the muzzle
area until last.
Anatomy of the Trigeminal Nerve
Peripheral course of 5th Nerve :

The motor and sensory nerve roots emerge separately
from the lateral aspect of the brain stem at the mid
pontine level. The gasserian ganglean of the sensory root
contains bipolar sensory nuclei and lies on the apex of
the petrous bone in the middle fossa.

Here the 3 divisions of the 5th nerve emerge. Each passes
through its own foremen and carries sensation from a
specific area of the face

Ophthalmic division passes through the superior orbital
fissure divides into branches with in the orbit and
emerges from the supra orbital foramen to innervate the
forehead.

Maxillary division passes through the foramen
rotundum into the pterygo palatine fossa, then through
the infro orbital foramen to become the infra orbital
nerve

The mandibular division exists from the foramen ovale
the anterior division incorporates the motor branch of
the 5th nerve innervating the muscles of mastication –
massater, pterygoids and temporalis – as well as
innervating the cheeks and gums (buccal nerve)

The lingual branch of the posterior trunk innervates the
anterior 2/3rd of the tongue and is joined by the chordi
tympani from the facial nerve carrying salivary secreto
motor fibers and taste from the anterior 2/3rd of the
tongue.
Diseases of the 5th Nerve
Causes of the 5th nerve lesions :

At the level of pons :
-
When associated with other cranial nerve palsies and
long tract signs
*
Vascular
*
Neoplastic
*
Demyelination
*
Syringobulbia
(especially dissociated sensory loss)


At the level of petrous apex :
-
6th nerve palsy
-
Petrositis (gradenigo’s syndrome)
At the level of cerebello pontine angle
-
Associated with other cranial nerve palsies with or
without long tract signs
-
Acoustic neuroma
-
Trigeminal neuroma
-
Subacute (chronic) meningitis

At the level of
- orbital fissure
- orbit
- cavernous sinus

1st division of the
5th nerve with or
without 3rd, 4th, 6th
nerver palsies
At the level of skull base :
one or more 5th nerve divisions will be involved
-
Nasopharyngeal or metastatic carcinoma
-
Trauma
Syndromes of 5th nerve lesions :

Sensory trigeminal neuropathy

Mental neuropathy

Infra orbital neuropathy

Gradenigo’s syndrome

Neuropathic Keratitis
Trigeminal neuralgia (tic douloureux)
Symptoms :

Paroxysmal attacks of severe, sharp, stabbing pain
affecting one or more divisions of the 5th nerve

The pain involves 2nd or 3rd divisions more often than the
1st. It rarely occurs bilaterally and never simultaneously
on each sign

Paroxysmal attacks last for several days or weeks, they
are often super imposed on a more constant ache. When
attacks settle the patients may remain pain free for many
months.

Chewing, speaking, washing the face, tooth
brushing, cold winds are touching a specific
‘trigger spot’. Eg., Upper lip or gum may
precipitate an attack of pain.

Trigeminal neuralgia more commonly affects
females and patients over 50 years of age.
Aetiology :

Trigeminal pain may be symptomatic or disorders which
affect the nerve root or its entry zone.
-
Root or root entry zone compression
* Arterial vessels often abut and some times clearly
indent the 5th nerve root at the entry zone into the
pons causing ephaptic transmission (short
circuiting)
* Tumours of the CP angle lying the against the 5th
nerve roots. Eg., Meningioma, frequently present
with trigeminal pain
-
Demyelination
* Such a lesion in the pons should be considered in a
young person with trigeminal neuralgia
Investigations :

CT or preferably MR Scan
Management :

Drug Therapy
-
Carbamazepine throughs affective in most patients
and helps confirm the diagnosis. Dosage is increased
until the pain relief occurs (600mg – 1600 mg / day)
-
Toxicity - drowsiness, ataxia
-
When remission established drug treatment can be
discontinued.
- If the pain control is limited other drugs. Eg.,
Baclofen, Lamotrigine, Gabapentin, Phenytoin may
benefit.
Other Therapies :

Operative therapy
-
Peripheral nerve techniques – Nerve block with
alcohol or phenol provides temporary relief.
Avulsion supra or infra orbital nerves gives more
prolonged relief
-
Radio surgical lesion of the trigeminal ganglion
provides another alternative for high risk surgical
patients
-
Trigeminal root section through either a
subtemporal or posterior fossa approach, the
appropriate trigeminal root is identified and divided
-
Microvascular decompression – exploration of the cp
angles reveals blood vessels in contact with the
trigeminal nerve root or root entry zone, separation
of these structures and insertion of a non-absorbable
sponge produces pain relief.
-
Radio frequency thermocoagulation – under general
anaesthetic produces a permanent lesion usually
resulting in analgesia of the appropriate area with
retention of light touch.
Results & Complications :

Pain relief – approximately 80-85% patients remain
pain free for a 5 year period. Although some may
relapse in the long term particularly after balloon
compression or glycerol injection. Results of peripheral
nerve avulsion or less satisfactory with pain recurring in
50% within 2 years

Dysaesthesia / Anaesthesia Dolorosa – This troublesome
sensory disturbance follows any destructive technique to
the nerve or root in 5-30% of the patients.
Microvascular decompression avoids this problem.

Cornial anaesthesia – This occurs when root section or
thermo coagulation involves the first division and
keratitis may result.

Mortality – Microvascular decompression and open roof
section carry a very low mortality < 1%.
Treatment Selection :

In most centers absence of sensory complications make
microvascular decompression the procedure of choice
particularly for first division pain and for younger
patients.

Frail and elderly patients may tolerate glycerol injection
balloon compression and thermo coagulation more
easily.