Intratemporal course of facial nerve

anatomy of facial nerve, applied anatomy of facial nerve

1. Intratemporal facial nerve Dr Safika Zaman Post Graduate Trainee Dept of ENT & Head Neck Surgery

2. Facial nerve Nerve of 2 nd branchial arch Facial nerve affects non verbal humanistic expression. Normal daily functions, such as eating and drinking. May disrupt the protective function of the eye.

3. introduction Facial nerve has the longest and complex course in its bony canal. The anatomical variations make the nerve prone to injury during mastoid surgeries. Having a thorough anatomical knowledge and its variations is must for the surgeons to avoid injury to this vital structure and for the safe surgery. The reported rate of iatrogenic injury to the facial nerve in primary tympanomastoidectomy surgeries was 0.6% to 3.7%. The risk is doubled in revision surgeries to 4% to 10%. Kalaiarasi R, Kiran A Satya, Vijayakumar C, et al. (August 02, 2018) Anatomical Features of Intratemporal Course of Facial Nerve and its Variations. Cureus 10(8): e3085. DOI 10.7759/cureus.3085

4. origin Facial nucleus is represented in the precentral gyrus of cerebral cortex. Fibres run down through genu of Internal Capsule. Nucleus:1. The motor nucleus of the facial nerve. 2. The superior salivatory nucleus 3. The nucleus solitarius , 4. Spinal tract of 5 th nerve

5. Functional anatomy Four major functions General somatic efferent :motor supply to facial muscles. General visceral efferent :parasympathetic secretomotor supply to submandibular and sublingual salivary glands and the lacrimal gland. Special visceral afferent :taste sensation from anterior two-thirds of the tongue. General somatic afferent :cutaneous sensations from the pinna and the external auditory meatus.

6. Overview of functional anatomy

7. course 1. Intracranial 2. Intra-temporal 3.Extra-temporal

8. Intracranial cource The facial nerve is smaller in diameter than the vestibulocochlear nerve (l.8 mm versus 3 mm). The facial nerve then crosses the cerebellopontine angle (a distance of 15 to 17 mm) with the eighth cranial nerve. Nerve of Wrisberg ( nervus intermedius).,

9. Rotation of 7 th and 8 th nv complex

10. iac The length of the IAC portion of the nerve is approximately 8 to10 mm

11. Meatal foramen & labyrinthine segment The facial nerve enters the labyrinthine segment of its fallopian canal through the meatal foramen . Meatal foramen is the narrowest portion of the entire canal and measures approximately 0.68 mm in diameter. The labyrinthine segment ( 4 mm in length ) makes up the first segment of the bony fallopian canal and is the narrowest and shortest portion of the canal. A dense band encircles the nerve at the lateral end of the IAC. This band contributes to the anatomic " bottleneck “ .

12. Geniculate ganglion The facial nerve takes a sharp ( 75 degree ) posterior turn at the first genu. The GG contains bipolar ganglion cells for the sensory functions of the nervus intermedius. The greater superficial petrosal nerve arises from the GG and en1erges through the hiatus of the fallopian canal (facial hiatus) onto the floor of the middle fossa.

13. greater superficial petrosal nerve With Deep petrosal nerve, forming the nerve of the pterygoid canal - also called the Vidian nerve. The parasympathetic fibers synapse at the pterygopalatine ganglion Vasomotor innervation to the lacrimal, nasal, and palatine glands.

14. TYMPANIC SEGMENT Courses posterio -inferiorly in its tympanic (horizontal) segment. Measures 1 l mm in length. Portion of the tympanic segment becomes the cephalad margin of the oval window niche. The nerve then takes a second turn (the second or external genu). At 2 nd genu, the facial nerve gives off a branch to the stapedius muscle.

15. Nerve to the stapedius Supplies the stapedius muscle. Contraction of the stapedius muscle stiffens the middle ear ossicles and tilts the stapes in the oval window of the cochlea; this effectively decreases the vibrational energy transmitted to the cochlea.

16. Mastoid segment The facial nerve then proceeds vertically in the mastoid cavity. which measures 13 mm in length. Approximately midway in its mastoid segment, the facial nerve gives off the chorda tympani nerve.

17. The chorda tympani posterior colliculus. The chorda tympani goes between the malleus and incus and re-emerges anterior to the middle ear cavity. It then enters medially to the temporomandibular joint through the petrotympanic fissure. the chorda tympani joins the lingual nerve, after exiting the petrotympanic fissure, 

18. Stylo -mastoid foramen At stylomastoid foramen, it becomes encircled by the fibrous tendon of the digastric muscle, which becomes part of the nerve sheath and firmly attaches the nerve to surrounding structures .

19. Extra temporal segment The extratemporal portion of the nerve divides into the temporofacial and cervicofacial trunks.

20. vascular supply of facial nerve Three branches of arteries have numerous anastomoses and constitute the extrinsic vascular system. Veins accompany the arteries in the fallopian canal. An intraneural vascular plexus (intrinsic system) originates from the extrinsic system. This plexus can support segments of the nerve when it is mobilized.

21. Landmarks in middle ear The cog identifies the 1 st genu. Cochleariform process is immediately inferior to the nerve. The nerve lies above the oval window. LSC is posterosuperior

22. Surgical landmark of the facial nerve Tragal pointer: Nerve is located about 1cm medial. Tympanomastoid suture: Nerve lies deep to the suture. The styloid process: lateral to the styloid process at skull base.

23. Anatomical variation of fn and its canal Congenital bony dehiscence: Most frequent site is above the oval window. There may be more than one dehiscence. Severe dysplasias of middle ear is associated with aberrant course of the nerve.

24. Cont … The canaliculer segment may enter petrous pyramid instead of IAM. Bifurcation of labyrinthine segment. FN crossing superiorly to LSC. FN over oval window. Hypoplasia of the nerve

25. Fn appearance in cortical mastoidectomy

26. radiology

27. radiology Clinical anatomy of the chorda tympani:a systematic reviewL J MCMANUS1, P J D DAWES2, M D STRINGER1 1Department of Anatomy, Otago School of Medical Sciences, and 2 Department of Otorhinolaryngology and Head and Neck Surgery, Department of Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand

28. Topodiagnostic testing of facial nerve Topodiagnostic testing,eg , Taste and saliva testing, Schirmer's tear test, Stapedial reflex test, Submandibuler salivery flow test These tests has been replaced by more objective and accurate investigations. Topodiagnostic tests evaluate different functions of the nerve to determine the site of the abnormality or lesion.

29. Applied anatomy Upper motor vs Lower motor paralysis.

30. Applied anatomy CP Angle lesion:The close anatomical relationship between the motor root of the facial nerve,nervus intermedius and vestibulocochlear nerve along theircisternal and meatal portions explains the disturbances in lacrimation, taste, salivary flow, hearing, balance or facial motor control that may result from lesions in either the CPA or IAM.

31. Applied anatomy Trauma: 80% of fructures are longitudinal, from blows to the temporal or parietal areas, Fructure line is usually anterior to otic capsule, usually facial is spared, usually there is delayed onset facial nv paralysis due to edema .

32. Applied anatomy Hemifacial spasm: symptom complex of unilateral facial nerve hyperactive dysfunction, characterized by the onset of mild and intermittent spasm of orbicularis oculi. Secondary hemifacial spasm may occur secondary to nerve trauma.

33. Applied anatomy- Ischemia of labyrinthine segment It is the only segment of the facial nerve that lacks anastomosing arterial cascades and so is vulnerable to embolic phenomena, low-flow states and vascular compression: it is most likely to be affected by ischaemia in the event of oedema following trauma or inflammation

34. Applied anatomy The geniculate ganglion lies in a fossa covered by a very thin layer of bone that separates it from the floor of the MCF. Dehiscences here are not uncommon: when present they render the nerve vulnerable during middle fossa surgery

35. Thank you