TRIGEMINAL NERVE AND ITS COURSE OF PATH IN SKULL

TN IS ONE OF IMPORTANT DIASEASE OF OROFACIAL PAIN

1. TRIGEMINAL NERVE Presented by :- Nirali Vaidya Parth Panchal Jahnavi Patel Siddhant Vasoya Guided by :- Oral and M axillofacial S urgery D epartment .

2. INTRODUCTION There are 12 pairs of cranial nerves. Trigeminal nerve is fifth cranial nerve. It is the largest of all cranial nerves It carries both sensory (afferent) and motor (efferent) fibres. Trigeminal Nerve attaches to pons, medial to middle cerebellar peduncle. Three large areas of the face are supplied by the three divisions of the trigeminal nerve. That is V1(opthalmic division),V2 (Maxillary division) and V3 (Mandibular division) . Embryologically, each division is associated with the developing facial process i.e. the ophthalmic division associated with frontonasal process, maxillary division associated with maxillary process and mandibular nerve with mandibular process.

3. TRIGEMINAL NERVE ANATOMY Trigeminal nerve arises with a larger sensory and a smaller motor root from the ventral surface of cerebral pons at the boundary between its body and arm. The dural compartment widens considerably anteriorly to accommodate the sensory root ganglion of the trigeminal nerve, the semilunar or the gasserion ganglion. Ganglion is present in the Meckle’s cavity partly in the lateral wall of cavernous sinus and partly on the anterior slope of temporal pyramid. The semilunar ganglion is crescent shaped, its concavity facing backward and upward into the concave margin enter fanwise the sensory root fibres and from the convexity arise the three sensory divisions of trigeminal nerve.

4. FUNCTION The sensory function of trigeminal nerve is to provide tactile, proprioceptive and nociceptive input for face and mouth. The motor function activates muscles of mastication, tensor veli palatini, tensor tympani, mylohyoid and anterior belly of digastric.

5. NEURAL TUBE- NUCLEI AND COLUMNS The neural tube is divided into two parts- dorsal alar plate and ventral basal plate by a sulcus called as sulcus limitans. The dorsal alar plate is sensory and ventral alar plate is motor and hence dorsalalar plate gives rise to sensory nuclei and basal plate gives rise to motor nuclei. In the brainstem, as the 4 th ventricle develops it pushes the alar plate laterally thus giving rise to various afferent and efferent columns. When same type of nuclei are arranged in a single line it forms columns.

6. Columns GSE- General somatic efferent column supplies extraocular and tongue muscles. SVE – Special Visceral efferent column supplies muscle from pharyngeal arches. GVE- General Visceral efferent column supplies smooth muscles and glands of head and neck GVA- General visceral afferent column carries general sensations from the viscera. SVA- Special visceral afferent column carries special sensation from the viscera and taste is the only special sensation coming from the viscera. GSA- General somatic afferent column carries general sensations like stretch, pain, proprioception, temperature, touch, pressure from the body wall. SSA- Special somatic afferent column carries olfaction, vision and hearing/ balance.

7. TRIGEMINO THALAMIC PATHWAY Ophthalmic, maxillary and sensory division of mandibular nerve goes into the trigeminal ganglion and from there the central fibres come and project into different part of trigeminal nuclei depending upon what type of sensation they are carrying. Eg- Proprioception goes into mesencephalic nucleus, touch and pressure goes into principal or chief sensory nucleus and pain and temperature goes into spinal nucleus. Trigeminal ganglion is 1 st order neuron. From the trigeminal nucleus 2 nd order neuron arises and decussates to the other side and then joins and then ascends upwards to relay in the thalamus by forming a lemniscus called as Trigeminal lemniscus. Applied aspect : Injury to trigeminal lemniscus leads to Contralateral loss of all sensations of face (pain, temperature,touch,pressure,proprioception)

8. TRIGEMINAL NERVE COURSE Trigeminal nerve is a mixed nerve containing V1,V2 and V3 divisions. V1 is sensory (Ophthalmic), V2 is sensory (Maxillary) and V3 is mixed (Mandibular). Columns – SVE as it supplies muscles of mastication and GSA column as it carries general sensation from the face. Trigeminal nerve arises from the trigeminal ganglion which is present in the petrous part of temporal bone called as Meckel's cave.

9. OPTHALMIC BRANCH (V1)

10. Ophthalmic nerve goes into the superior orbital fissure(SOF) through the lateral wall of cavernous sinus. This nerve divides into three branches namely Frontal nerve, Naso ciliary nerve and Lacrimal nerve before entering into the SOF. The Frontal nerve as it exits the orbit divides further into 2 branches namely supratrochlear and supraorbital nerve. Supraorbital supplies the skin of forehead and scalp and supratrochlear supplies skin of the upper eyelid and lower part of forehead. Naso ciliary nerve is topographically connected to Ciliary Ganglion and it divides into 2 branches namely Anterior ethmoidal and Posterior Ethmoidal nerve Lacrimal nerve supplies the lacrimal gland and the conjunctiva, skin and upper eyelid. Zygomaticotemporal nerve is branch of maxillary nerve, connecting the maxillary nerve to lacrimal nerve. OPHTHALMIC BRANCH

11. OPHTHALMIC DIVISION NASOCILIARY NERVE: - BRANCHES: Ant ethmoidal nerve post. Ethmoidal nerve long cilliary nerve infratrochlear nerve FRONTAL NERVE : Supraorbital nerve Supratrochlear nerve LACRIMAL NERVE:- This is the external branch of first trigeminal division. In its course it receives the branch from zygomatic nerve. Connecting branch contains postganglionary parasympathetic fibres from the pterygopalatine ganglion which reach the lacrimal gland via the lacrimal nerve. Then it reaches the upper eyelid near the outer corner of eye and supplies lateral part of upper eyelid and adjacent skin.

12. APPLIED ASPECT NASOCILIARY NERVE: Loss of corneal reflex also known as decreased or absent corneal blink reflex occurs when there is a damage to the nasociliary branch of trigeminal nerve. The sensory pathway of the trigeminal nerve carries the sensation of touch from the cornea to the brainstem. HERPES ZOSTER OPHTHALMICUS :- Most frequently affects the naso ciliary branch. It is a recurrent neurocutaneous infection caused by HHV3 /Varicella zoster.

13. LACRIMAL NERVE: Damage or dysfunction of the lacrimal nerve and gland can lead to dry eye syndrome, a common condition characterized by insufficient tear production, resulting in discomfort, blurry vision, and surface damage to the eye. Surgical Considerations: Surgeons must be cautious during orbital procedures to avoid injuring the lacrimal nerve, which could result in loss of sensation to the upper eyelid or impairment of tear production. FRONTAL NERVE: Frontal nerve damage can lead to sensory loss of the affected areas of skin.

14. The maxillary nerve comes out of the cranial cavity through foramen rotundum in the pterygopalatine fossa and then it runs through the roof of the maxilla and ultimately comes out as infraorbital nerve. MAXILLARY BRANCH

15. MAXILLARY BRANCH COURSE-IMPORTANT LANDMARKS Arise from trigeminal ganglion which is present in the apex of petrous part of temporal bone called as Meckel's cave. Runs forward in lateral wall of cavernous sinus below the ophthalmic nerve. It leaves the middle cranial fossa through foramen rotundum. Foramen rotundum is a communication between the middle cranial fossa and pterygopalatine fossa. It reaches the upper part of pterygopalatine fossa. Maxillary nerve as it traverses through the pterygopalatine fossa has strong communication with the pterygopalatine ganglion through ganglionic branches. It moves anteriorly through the inferior orbital fissure and then enters into the floor of orbit. From here it continues as infraorbital nerve.

16. The infraorbital nerve passes through the groove and then it moves forwards to enter into infraorbital canal. The nerve then emerges through the infraorbital foramen. It then gives off terminal branches namely palpebral, nasal and labial branches. Inferior palpebral supplies the skin and conjunctiva of lower eyelid. Nasal nerve supplies nasal septum and nasal wall. Superior labial supplies skin and mucosal surface of upper lip.

17. MAXILLARY DIVISION BRANCHES IN MIDDLE CRANIAL FOSSA:- Meningeal branch IN PTERYGOPALATINE FOSSA:- Ganglionic branches, zygomatic and posterior superior alveolar IN INFRAORBITAL CANAL:-Infraorbital branch[ middle superior alveolar and anterior superior alveolar] ON FACE:- Terminal [palpebral, nasal, labial]

18. MAXILLARY DIVISION NERVES MENINGEAL BRANCH:-Before it exits the middle cranial fossa through the foramen rotundum it gives off a branch called as meningeal branch which supplies the dura mater of middle cranial fossa. GANGLIONIC BRANCHES:-In the pterygopalatine fossa the maxillary nerve gives of two branches which connects to the pterygopalatine ganglion called as ganglionic branches.

19. ZYGOMATIC NERVE:- Branch of maxillary nerve given off in pterygopalatine fossa. It enters the orbit through lateral end of inferior orbital fissure and runs along the lateral wall, outside the periosteum, to enter the zygomatic bone. Just before or after entering the bone, it divides into 2 terminal branches, zygomaticofacial and zygomaticotemporal nerve which supply the skin of face and anterior part of temple. POSTERIOR SUPERIOR ALVEOLAR NERVE:-Enters the posterior surface of the body of maxilla and then supplies the three upper molar teeth and the adjoining gums. MIDDLE SUPERIOR ALVEOLAR NERVE:-Arises in infraorbital groove and runs in lateral wall of maxillary sinus and supplies the upper premolar teeth. ANTERIOR SUPERIOR ALVEOLAR NERVE:-Arises in infraorbital canal and then runs in anterior wall of maxillary sinus to supply the upper incisor, canine teeth, maxillary sinus and Antero inferior part of nasal cavity.

20. The nasopalatine nerve is a sensory branch of the maxillary division of the trigeminal nerve ( CN V2) . It arises from the maxillary nerve, travels through the pterygopalatine ganglion, passes through the sphenopalatine foramen into the nasal cavity, and then descends along the nasal septum to exit into the oral cavity via the incisive canal to innervate the anterior hard palate and gingiva of the incisor teeth. INFRAORBITAL NERVE:- Continuation of maxillary nerve.it enters the orbit through inferior orbital fissure. It then runs on the floor of orbit at first ion infraorbital groove and then in the infraorbital canal. It then emerges on face through infraorbital foramen and terminates by dividing into inferior palpebral, nasal and superior labial branches.

21. APPLIED ASPECT INFRAORBITAL NERVE BLOCK:- Complications from an infraorbital nerve block may include bleeding, hematoma formation, infection, injury to the artery or vein, unintentional injection of anesthetic into the artery or vein, nerve damage, or edema. Special considerations include avoiding injection into the infraorbital foramen, as this could lead to long-term neuropathy due to nerve compression, damage to the orbital floor, or injury to the orbit. If there is any suspicion of orbital damage, immediate consultation with ophthalmology is required. Allergic reactions to the anesthetic medication can occur during the procedure, and management should be supportive based on the affected organ systems.

22. Complications from PSA NERVE BLOCK includes hematoma, swelling, trismus, infection. Less common but more serious are ocular complications such as diplopia, ptosis(drooping eyelid) from anaesthetic spread into nearby vascular networks. Complication from zygomatic nerve injury can lead to numbness, tingling, loss of sensations in areas including lower eyelid, cheek and upper lip. The zygomatic nerve also provides innervation to lacrimal gland so it can lead to dry eye. Nasopalatine nerve injury can lead to tingling in anterior palate and upper incisor region along with pain, bleeding and infection. Loss of sneeze reflex can occur if there is a damage to maxillary nerve as it carries general sensations from nasal mucous membrane.

23. Mandibular Nerve The third division of the trigeminal nerve is a mixed nerve and contains the entire motor portion. The mandibular division, the strongest of the three divisions of the trigeminal nerve, leaves the skull through the oval foramen and enters the infratemporal fossa. Below the oval foramen the mandibular nerve is in closerelation to the anterolateral, membranous wall of the auditive or Eustachian tube. To the medial circumference of the third division is attached the otic ganglion. At their origin, motor and sensory branches of the mandibular nerve cannotbe  entirely separated.

24. MANDIBULAR DIVISION

25. Masseteric Nerve. This nerve leaves the trunk of the third division at its lateral circumference close to the cranial base. It runs laterally between the infratemporal surface of the greater sphenoid wing and lateral pterygoid muscle, passes behind the tendon of the temporal muscle through the mandibular notch, and enters the masseter muscle from its deep surface. Posterior and Anterior Temporal Nerves- The posterior temporal nerve arise from the mandibular nerve close to, or together with, the masseteric nerve. Anterior temporal nerve is at its origin, as a rule, united with the buccal nerve. The common trunk turns anteriorly and slightly laterally in a groove on the anterolateral circumference of the oval foramen.

26. MEDIAL PTERYGOID NERVE: This nerve, the nerve for the medial pterygoid muscle, arises from the anteromedial circumference of the mandibular division and is, in most persons, connected closely with the otic ganglion or passes through it. LATERAL PTERYGOID NERVE:- This nerve, destined to supply the lateral pterygoid muscle, is, in most persons, at first incorporated into the buccal nerve and branches off where the buccal nerve passes between the two heads of the lateral pterygoid muscle. The fibers enter the lateral pterygoid muscle immediately after their separation from the buccal nerve. BUCCAL NERVE:- This nerve leaves the trunk of the mandibular nerve at its anterolateral circumference. In its first part it is combined with motor fibers which will constitute the anterior temporal and the lateral pterygoid nerves. Then the buccal nerve crosses the superior head of the lateral pterygoid muscle on its medial side and turns laterally between the two heads of this muscle. At this point the buccal nerve releases the fibers which enter the lateral pterygoid muscle.

27. AURICULOTEMPORAL NERVE:- The nerve separates from the trunk of the third division immediately below the base of the skull, turns almost directly backward, and encircles with two branches the middle meningeal artery. Then the auriculotemporal nerve crosses the neck of the mandible and enters the parotid gland, where it divides into two almost equal branches. One branch bends sharply upward and continues its course in front of the cartilage of the outer ear between the superficial temporal artery and vein. It reaches the temporal region after crossing the root of the zygomatic arch. Small branches of the auriculotemporal nerve supply the capsule of the mandibular joint and others enter the substance of the parotid gland. The second, inferior branch of the auriculotemporal nerve is sometimes split into two or three twigs.It turns in the substance of the parotid gland downward and joins facial nerve.

28. Auriculotemporal supplies upper 2/3 rd of auricle, skin of temple, TMJ and parotid gland. Lingual nerve carries the general sensations from the anterior 2/3 rd of tongue. Inferior alveolar nerve goes inside the mandibular canal and comes out as the mental nerve to supply the skin of chin. Before inferior alveolar nerve goes in the mandibular canal, it gives off a branch which supplies two muscles namely Mylohyoid and Anterior belly of digastric.

29. LINGUAL NERVE: -Below the oval foramen, this nerve is united closely with the inferior alveolar nerve. Separating from the alveolar nerve, usually 5 to 10 mm. below the cranial base, the lingual nerve lies anterior and slightly medial to the inferior alveolar nerve. If the ligament intervenes between the two nerves, thelingual nerve is found on the medial, the alveolar nerve on the lateral side of the ptergospinous ligament.

30. INFERIOR ALVEOLAR NERVE:- It winds around the lower border of the lateral pterygoid muscle, which separates the alveolar nerve from the mandibular ramus, and then turns sharply outward and downward to reach the inner surface of the mandible at the mandibular foramen which it enters. Before the nerve disappears into the canal of the mandible, it releases the mylohyoid nerve . This small nerve turns downward and anteriorly in the mylohyoid groove of the mandible, which is bridged by a ligament, partial ossification of which is not rare. Leaving the mylohyoid groove, the mylohyoid nerve converges with the submental artery and vein in the submandibular niche and approaches the inferolateral surface of the mylohyoid muscle near its posterior border. The lower alveolar nerve passes through the length of the mandibular canal and divides in the premolar region into its two unequal terminal branches, the incisive and the mental nerves. The mental nerve leaves the body of the mandible through the mental canal; emerging at the mental foramen, the mental nerve usually divides into three branches. One branch turns forward and downward to the skin of the chin. The other two branches course anteriorly and upward into the lower lip where they supply the skin and mucous membrane of the lip and mucosa on the labial alveolar surface. The incisive branch is one of the dental branches of the inferior alveolar nerve.

31. APPLIED ASPECT INFERIOR ALVEOLAR NERVE BLOCK :- areas anaesthetized- mandibular teeth to the midline, all the hard and soft tissues to the midline including the floor of the mouth and anterior 2/3rds of the tongue. Indicated when multiple teeth are to be extracted in one quadrant of mandible. Complication includes hematoma, trismus and transient facial paralysis. MENTAL NERVE BLOCK :- areas anaesthetized: buccal mucous membrane anterior to mental foramen and skin of lower lip and chin. Indicated in soft tissue biopsies and suturing of soft tissues. Complication includes hematoma.

32. TRIGEMINAL NEURALGIA The prototypic neuropathic facial pain is trigeminal neuralgia. Trigeminal neuralgia also known as Tic Douloureux or painful tic or Fothergills disease occurs most frequently in female patients over 50 years of age.( female to male ratio 1.6:1) TN usually occurs with sharp, electric shock like pain in the face or the mouth with pain being intense and lasting for brief periods of seconds to minutes followed by a refractory period during which the pain cannot be reinitiated. Usually a trigger zone is present where any stimuli such as soft touch can also provoke an attack. Common trigger zones- corner of lips, cheek, ala of nose and lateral brow. Any intraoral site may also be a trigger zone including teeth, gingiva or tongue. V3 commonly involved as compared to V2.

33. TN CLINICAL CHARACTERISTICS 1) Severe paroxysmal pain 2) Unilateral location right>left 3) Mild stimuli provokes pain 4) V2 and V3 dermatomes most affected 5) Frequently pain free between attacks 6) No neurological deficits 7) Local anaesthesia of trigger zone temporarily arrests pain ETIOLOGY: cause is not entirely clear but the consensus is that pressure on the root entry zone of the trigeminal nerve by a vascular loop leads to focal demyelination which in turn precipitates ectopic or hyperactive discharge of the nerve.

34. During an attack, the patient grimaces with pain, clutches his hands over the affected side of the face. Male patients avoid shaving. Patients also avoid brushing the teeth. In extreme cases, the patient will have a frozen or a mask like face. The attacks do not occur during sleep. Many patients will lead a very poor quality of life due to excruciating pain. It is very common for these patients to undergo indiscriminate dental extractions on the affected side without any relief from pain, because the fibre distribution often mimic pain of odontogenic origin. DIAGNOSIS- based on history of shooting pain along the branch of nerve precipitated by touching a trigger zone. A routine cranial nerve examination would be normal but sensory or motor changes may be evident in patients with underlying tumours or other CNS pathology. Local anaesthetic blocks may also prove to be useful in diagnosis Enhanced MRI of the brain is indicated to rule out tumours, multiple sclerosis and vascular malformations. Magnetic resonance angiography may be needed to detect difficult to visualize vascular abnormalities.

35. MANAGEMENT Anticonvulsants are most effective. Carbamazepine is the most commonly used drug but skin reactions like generalized erythema mulktiforme are serious side effects. Oxcarbazepine is the analogue which causes very little hepatic induction and has lower risk of blood dyscrasias as compared to carbamazepine. Pregabalin, gabapentin may also be useful in treatment but are not as reliable as carbamazepine or oxcarbazepine. Use of Sumatriptan has also recently shown promise in management of TN. Other drugs that have been effective include phenytoin, lamotrigine, baclofen, topiramate. Surgical approach includes peripheral surgery on trigeminal nerve branch that triggers attack. It is usually effective for 12 to 18 months. The most commonly performed procedure at the level of gasserion ganglion is Percutaneous radiofrequency thermocoagulation or compression of the ganglion by balloon miocrocompression (percutaneous rhizotomy). The most extensively studied surgical procedure includes microvascular decompression of nerve root at the brainstem.

36. TRIGEMINAL NERVE ASSESSMENT-JAW JERK REFLEX The jaw jerk reflex also known as the masseter reflex is a stretch reflex in which the jaw muscles (masseter and temporalis) contract in response to tap on the chin. This involuntary action, which causes a subtle jerk of the jaw is mediated by trigeminal nerve and is a monosynaptic reflex .

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