evaluation of nerve injury, extratemporal course

1. Facial Nerve(extra temporal)
& Tests
Dr Safika Zaman
Dept of ENT & Head Neck Surgery
VIMS,RKMSP

2. INTRODUCTION
 Extratemporal course of the facial nerve is important for surgery of parotid
and other tumors in the infratemporal space.
 Complex and variable anatomy.
 Knowing the variability and specific characteristics of each branch, will
help the surgeon to identify risk points.

3. EXTRATEMPORAL ANATOMY
 Posterior Auricular nerve: part of EAC. TM,
Auricular muscles.
 Branches to digastic & stylohyoid muscle.

4. EXTRATEMPORAL ANATOMY
 From stylomastoid foramen, curves
downward and ventrolateral and enters
the retromandibular fossa lateral to the
external carotid artery and the
retromandibular vein..
 stylomastoid foramen to division length is
15 to 20 mm.
 Inside the parotid gland, the nerve runs
between the deep and superficial lobe
until it emerges beyond the anterior border
of the gland.

5. PAROTID GLAND & FACIAL NERVE

6. TERMINAL BRANCHES
Temporal branch – innervates the frontalis and
orbicularis oris muscles and the muscles in the
upper part of the face.
Emerges at the superior border of the parotid
gland and crosses over the zygomatic arch to get
the fronto-orbital region.
Zygomatic branch – innervates the middle part of
the face.
Zygomatic branch runs below and parallel to the
zygomatic arch to the orbito-nasal area.

7. TERMINAL BRANCHES
 Buccal branch – innervates the cheek
muscles, including the buccinator muscle. It
runs parallel to the parotid duct to get the
buccinator muscle.
 Mandibular branch – innervates muscles of the
lower part of the face. It run over the facial
vessels in the lower third of the mandible to
get the inferior lip.
 Cervical branch – innervating the muscles
below the chin and, among others, the
platysma muscle. It run downward to get the
platysma muscle

8. LANDMARKS
The FTN is at high risk of injury
during surgical procedures such
as facelift, cutaneous surgery
and bicoronal approaches for
craniofacial surgical access.
Pitanguy’s line, defined by a line
drawn from a point 0.5cm
inferior to the tragus to a point
1.5 cm superior and lateral to
the eyebrow

9. Extracranial Course of the Facial
Nerve Revisited
PAULA MARTINEZ PASCUAL,1 EVA MARANILLO,2 TERESA VAZQUEZ ,2
CLARA SIMON DE BLAS,3 JOSE MARIA LASSO,4
AND JOSE R. SANUDO 2*

10. PATTERNS OF TERMINAL BRANCHING
 Different classification systems are mainly based on
three criterion
1.connections
2.buccal branch origin
3.facial nerve number of trunks.
 These classifications are less practical at the moment of
dissection.

13. ANATOMICAL RELATIONSHIP OF FN IN ADULTS &
CHILDREN

14.  Extracranial
Course of the
Facial Nerve
RevisitedPAUL
A MARTINEZ
PASCUAL,1
EVA
MARANILLO,2
TERESA
VAZQUEZ
,2CLARA
SIMON DE
BLAS,3 JOSE
MARIA
LASSO,4AND
JOSE R.
SANUDO 2*

15. HISTOLOGY

16. PATHOPHYSIOLOGY (Wallerian axon degeneration)
Wallerian degeneration is an
active process of
degeneration that results
when a nerve fibere is cut or
crushed and the part of the
axon distal to the injury.

17. PATHOPHYSIOLOGY

18. SEDDON & SUNDERLAND CLASSIFICATION

21. FACTORS AFFECTING NERVE RECOVERY
 Etiology and severity of the paralysis
 Duration
 Age
 Nutrition
 Blood supply
 Comorbidities ( eg, diabetes mellitus)
 Concurrent wound infection

22. CAUSES OF FACIAL PARALYSIS

23. EVALUATION OF FACIAL NERVE FUNCTION- HB
GRADING SYSTEM

24. EVALUATION OF PATIENTS WITH
FACIAL NERVE DISORDERS
 History: date of onset, rapidity,fprogression, comorbidities, risk
factors, duration of symptoms,and associated symptoms.
 Examination and grading :
 Tests: 1. Topographic Tests
2.Prognostic tests/electrodignostic tests
3. Imaging

25. ELECTROPHYSIOLOGIC TESTING
 Electromyography(EMG)
 Nerve excitability test(NET)
 Nerve conduction time(NCT)
 Maximal stimulation test(MST)
 Electro-neuronography(ENOG)

26. MERITS OF ELECTRODIAGNOSTIC TEST
 To detect subclinical early regeneration
 To differentiate birth trauma from embryonic causes
 Determining the completeness of neural blockade.

27. PRINCIPLE OF ELECTROMYOGRAPHY TEST
Electrophysiological measures in facial paresis and paralysis
Greg Mannarelli, AuD, Garrett R. Griffin, MD, Paul Kileny, PhD, Bruce Edwards, AuD

28. POSSIBLE RESPONCES OF ELECTROMYOGRAPHY
 Silent resting potential- denervated
muscle
 Volentary motor unit potential- with
activity
 Fibrilation potential- in degeneration
 Polyphasic re-innervation potential-
during reinnervation

29.  th
Citation
Michael J. Aminoff,
Richard B. Weiskopf;
Electrophysiologic
Testing for the
Diagnosis of
Peripheral Nerve
Injuries.
Anesthesiology 2004;
100:1298–1303 doi:
https://doi.org/10.109
7/00000542-
200405000-00034

30. NERVE CONDUCTION VELOCITY TEST
 Correlates with degree of myelination
 Less reliable

31. NERVE EXCITABILITY TEST
 The lowest electric current to elicit
facial twitch on paralyzed side of the
face is compared to the threshold
value of normal side.
 A difference of 3.5 mA suggests poor
prognosis.
 Drawback is only large fibers are
stimulated.

32. ELECTRONEURONOGRAPHY
 The ENOG examination was originally proposed and
popularized by Esslen and Fisch.
 The goal of the testing is to measure the amount of neural
degradation that has occurred distal to the site of nerve
injury by measuring the muscle response to an electrical
stimulus.
 The amount of denervation is represented by comparison
of the peak-to-peak amplitude of the CMAP from the
affected side with the response amplitude from the
nonaffected side

33. INTERPRETATION OF ENOG
 ENOG’s primary utility is in determining the long-term prognosis of
facial function.
 Patients with 90% degeneration on the affected side (when
compared with the nonaffected side) are considered to have a
positive test.
 ENOG cannot precisely differentiate second through fifth-degree
injuries.
 Prognostic value: May et al found that ENOG was 88% accurate in
predicting incomplete recovery when denervation was 75% or more.

34. Electrophysiolog
ical measures in
facial paresis
and
paralysis
Greg Mannarelli,
AuD, Garrett R.
Griffin, MD, Paul
Kileny, PhD,
Bruce Edwards,
AuD

35. DEMERITS OF ELECTRODIAGNOSTIC TEST
 Change in positioning
 EMG is not much in use in 1st 3wks after injury
 Temerature change
 Suboptimal stimulation mimics demyelinations

36. REPAIRED FACIAL NERVE RECOVERY SCALE

37. BELLS PALSY
 Bell’s palsy, also called idiopathic facial paralysis, is defined as an
acute-onset, isolated, unilateral, lower motor neurone facial
weakness.
 The reported annual incidence varies in different parts of the
world with estimates varying between 11 and 40 per 100 000
people.
 It is more common in people with diabetes.

39. FACIAL PARALYSIS IN CHILDREN
 The incidence is 1 to 2 per 1000 deliveries.
 Most common cause is birth trauma.
 The differentiation between acquired and congenital facial
paralysis must be detected.
 Syndromic causes include Mobius syndrome, Goldenhar syndrome
etc

40. IMAGING TESTS
 CT is preferable for imaging the lateral course of the facial nerve
upto the stylomastoid foramen.
 CT can detect deviations in the course and caliber of the
intratemporal facial nerve, which can provide key information
regarding facial nerve pathology
 CT is important in surgical planning for otologic surgery.

41. Cont…
 MRI can be used to image the facial nerve from the brainstem to
the fundus of the IAC.
 MRI ,to determine the presence of perineural spread from parotid
malignancies.
 The proximal extracranial portion of the facial nerve in the parotid
gland is best visualized with axial high-resolution T1-weighted
images using a microscopic coil.
 High-resolution T2-weighted or CISS images can directly visualize
the vascular loop and compressed facial nerve

42. Thank you