Download Pathology of the facial nerve: A pictorial review

Pathology of the facial nerve: A pictorial review
Poster No.:
R-0215
Congress:
2014 CSM
Type:
Scientific Exhibit
Authors:
P. F. Kwan, R. Thomas; SOUTH YARRA/AU
Keywords:
Head and neck, Anatomy, CT, MR, Contrast agent-intravenous,
Education, Education and training, Pathology
DOI:
10.1594/ranzcr2014/R-0215
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Page 1 of 18
Aim
Introduction:
Pathology affecting the facial nerve is often clinically devastating as the facial nerve
provides motor innervation to the muscle of facial expression. Imaging plays a crucial
role in the diagnosis of facial nerve pathology. However, radiologic diagnosis of facial
nerve pathology can be challenging due to meandering and complex anatomy of the
facial nerve.
Methods and materials
Anatomy of the facial nerve:
The facial nerve has a motor nucleus and two sensory nuclei (superior salivatory nucleus
(1)
and solitarius tract nucleus) which are located in the ventrolateral pontine tegmentum.
Motor fibers encircle the CN6 nucleus before emerges at the pontomedullary junction.
The superior salivatory nucleus sends parasympathetic secretomotor fibers as nervus
intermedius to the lacrimal, submandibular and sublingual glands. The solitary tract
nucleus receives taste from the anterior two third of the tongue, with fibers travelling
within the nervus intermedius.
Cisternal segment:
The motor nerve root joins the smaller sensory nervus intermedius, then emerges at the
root exit zone in pontomedullary juction and travels anterolaterally in the cerebellopontine
angle cistern.
Internal acoustic canal (IAC) segment:
From the porus accousticus, the facial nerve travels to the fundus of the IAC, in the
anterior superior quadrant, above crista falciformis and anteriorly to Bill's bar.
Labyrinthine segment:
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This segment of the facial nerve travels anterolaterally from the IAC fundus to the
geniculate ganglion (anterior genu). The greater superficial petrosal nerve arises from
the geniculate ganglion, carrying parasympathetic fibers to the lacrimal gland.
Tympanic segment:
From the geniculate ganglion, the tympanic segment travels to the posterior genu,
immediately beneath the lateral semicircular canal.
Mastoid segment:
Just distal to the pyramidal eminence (posterior genu), the nerve passes vertically
downwards to the stylomastoid foramen. It has several branches including:
1.
2.
Stapedius nerve supplies motor function to stapedius muscle.
Chorda tympani carries secretomotor fibers to the submandibular and
sublingual glands and taste fibers from anterior two thirds of tongue.
Extratemporal segment:
After exiting the stylomastoid foramen, this segment of the facial nerve gives off a sensory
branch that supplies part of the external accoustic meatus and tympanic membrane.
It then enters the parotid gland between the deep and superficial lobes, lateral to the
retromandibular vein. This segment of the facial nerve gives off five terminal motor
branches: temporal, zygomatic, buccal, mandibular and cervical.
Normal enhancement of the facial nerve:
The normal facial nerve can demonstrate enhancement along at least one segment
(2)
in 76% of cases, excluding the distal intrameatal and the labyrinthine segments.
The geniculate ganglion, greater superficial petrosal nerve and the proximal tympanic
(3)
segment generally demonstrate faint enhancement. The cisternal, meatal, labyrinthine,
and extracranial segments of the facial nerve do not normally enhance. Enhancement
of these segments should raise the possibility of pathological involvement. Asymmetrical
enhancement or irregular thickening of the geniculate ganglion, tympanic and mastoid
segments should also be considered pathological.
Page 3 of 18
Fig. 1: Facial nerve anatomy: Axial MRI images. a: IAC segment. b: labyrinthine
segment. c: geniculate ganglion. d: tympanic segment. e: mastoid segment.
References: Alfred Health - SOUTH YARRA/AU
Fig. 2: Facial nerve anatomy: Coronal CT images. a: IAC segment. b: "snake eyes"
appearance as the tympanic segment doubles back next to the labyrinthine segment
adjacent to the cochlea. c,d: labyrinthine and tympanic segments converge at the
geniculate ganglion. e: mastoid segment below the lateral semicircular canal. e:
mastoid segment in the stylomastoid canal.
References: Alfred Health - SOUTH YARRA/AU
Results
Common pathology affecting the facial nerve can be categorised as follow:
Page 4 of 18
•
•
•
•
•
•
Neoplasm
Infection
Inflammation/Idiopathic
Vascular
Trauma
Congenital
Neoplasm
Neoplastic process involving the facial nerve is rare. Several neoplastic processes which
commonly involve the facial nerve include facial nerve schwannoma, hemangioma,
perineural tumour spread from primary SCC or parotid gland malignancy, lipoma, glomus
tumour and lipoma.
Facial nerve schwannoma
Facial nerve schwannoma is a rare benign tumour of Schwann cells that can affect
anywhere along the facial nerve from its origin to its extracranial ramifications in the
parotid space of the extracranial head and neck. It often affects multiple segments of the
facial nerve with a predilection for the region around the geniculate ganglion. Patients
may present with gradual facial nerve paralysis over many years or sensorineural hearing
loss due to local mass effect from the tumour.
(4)
Imaging features:
Enhancing mass in the cerebellopontine angle/internal acoustic canal extending and
expanding into the labyrinthine canal ( "labyrinthine tail") and geniculate ganglion ( "icecream on cone" appearance). It is commonly iso to hypointense signal on T1 sequence
and high signal on T2 sequence. They frequently enhance homogeneously, if small,
and heterogeneously, if large. Large lesions may also demonstrate intramural cystic
degeneration.
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Fig. 3: Facial nerve schwannoma: Axial T1 post contrast images demonstrated an
enhancing mass in the internal acoustic canal extending into the labyrinthine canal with
an enlarged geniculate ganglion ( ice-cream on cone appearance).
References: Alfred Health - SOUTH YARRA/AU
Facial nerve haemangioma
Facial nerve haemangioma is a rare vascular malfomation, often arising from region
around the geniculate ganglion. Patients with hemangiomas that originate in the
geniculate fossa most often present with facial nerve paralysis that is slowly progressive
(5)
over the course of several weeks.
Sensorineural hearing loss and pulsatile tinnitus may
(6)
occur if there is erosion of the cochlear otic capsule.
Imaging features: Enhancing mass centred at the geniculate ganglion, with permeative
or honeycomb bone matrix on CT. Tumour size ranges from 2mm to 2cm. The lesion
may spread along the greater superficial petrosal nerve anteromedially if large.
Page 6 of 18
Fig. 4: Facial haemangioma: Enhancing mass centred at the geniculate ganglion on
contrast enhanced MRI, with permeative bone matrix on CT.
References: Alfred Health - SOUTH YARRA/AU
Perineural tumour spread
Several malignant tumours of the parotid gland can spread along the facial
nerve. These tumours include adenoid cystic carcinoma, mucoepidermoid carcinoma,
adenocarcinoma, malignant mixed tumors, acinic cell carcinoma, lymphoma, squamous
(7)
cell carcinoma and melanoma metastases.
Adenoid cystic carcinoma has the highest
(8)
tendency to cause perineural tumour spread (70 -75%)
and it is the most common
malignancy to cause perineural spread along the facial nerve.
Imaging features: Irregular, tubular enhancement along extracranial and intratemporal
segment of the facial nerve , extending from an enhancing intraparotid mass. The
perineural tumour spread may be contiguous or skipped and it can extend proximally up
to the cisternal segment.
Page 7 of 18
Fig. 5: Perineural tumour spread: Enhancing primary skin SCC with parotid nodal
metastasis and thickened, nodular perineural tumour spread along the extracranial and
mastoid segment of the facial nerve.
References: Alfred Health - SOUTH YARRA/AU
Glomus tumour
Glomus tumour, also known as paraganglioma, is a rare benign vascular tumour that
arises from the paraganglia cells. Depending on its location, glomus tumours of the head
and neck can be divided into glomus tympanicum, jugulare, vagale and carotid body
tumour. Facial nerve paralysis is a rare symptom/complication of glomus tympanicum
(5%). More common presentations are pulsatile tinnitus and conductive hearing loss.
Imaging features: Glomus tympanicum appears as an enhancing mass on the cochlear
promontory with "salt and pepper" appearance on MRI. Salt and pepper appearance
refers to punctate hyperintensity (salt) and flow voids (pepper) on T1 weighted images.
Small lesions may be difficult to see on CT, but large lesions cause permeative
destructive bone changes, with erosion of the middle ear cavity and ossicles. Glomus
jugulotympanicum may extend from the cochear promontory to the jugular foramen, with
the same imaging appearances described above.
Page 8 of 18
Fig. 6: Glomus jugulotympanicum : Enhancing tumour with "salt and pepper"
appearance, centred in the jugular foramen with permeative destructive bone changes
on CT. The tumour extends laterally involving the mastoid segment and superiorly
involving the IAC segment of the facial nerve.
References: Alfred Health - SOUTH YARRA/AU
Infection
Acute or chronic infection of the middle ear and mastoid can spread to the facial nerve
due to its course within the temporal bone. Cholesteatoma affecting the middle ear also
has the potential to erode into the intratemporal segment of the facial nerve.
Otomastoiditis
Acute or chronic otomastoiditis is an infection affecting the middle ear and mastoid air
cells, usually affecting young children and most commonly due to bacterial infection.
Complications of otomastoiditis are rare, as the disease is usually responsive to prompt
antibiotic treatment. However, complications of otomastoiditis may occur due to antibiotic
resistance, or in immunocompromised patients. The complications include coalescent
mastoiditis, petrous apicitis, labyrinthitis, facial nerve paralysis and hearing loss.
Page 9 of 18
Imaging features: Middle ear and mastoid opacification on CT. In coalescent mastoiditis,
there is erosion of the mastoid septation and cortex. On MRI, there is T1 isointense
and T2 hyperintense inflammatory debris, with diffuse enhancement within the middle
ear and mastoid. The facial nerve is most commonly affected in its tympanic and upper
mastoid segments. In cases of acute otomastoiditis, the lesion is often not destructive
(9)
and reversible.
Fig. 7: Acute otomastoiditis: Enhancing tissue in the middle ear and mastoid air cells.
There is also enhancement of the mastoid segment of the facial nerve which lies in the
region of the inflammatory phlegmon, in keeping with facial nerve involvement. Soft
tissue opacitication in the middle ear and mastoid air cells on CT. No erosion of the
mastoid septation and cortex to indicate coalescent mastoiditis.
Page 10 of 18
References: Alfred Health - SOUTH YARRA/AU
Inflammation/idiopathic
Several inflammatory/ idiopathic conditions are known to affect the facial nerve. These
conditions are Bell's palsy, Guillain-Barré Syndrome, sarcoidosis, multiple sclerosis and
wegener's granulomatosis.
Guillain-Barré Syndrome
Guillain-Barré Syndrome is an acute inflammatory demyelinating polyradiculopathy of
uncertain aetiology. Miller Fisher Syndrome is a variant of Guillain- Barré Syndrome
which involves the cranial nerves. Patients may present with the clinical triad of
opthalmoplegia, ataxia and areflexia. In most cases, multiple cranial nerves are involved,
and the facial nerve can be involved up to 27 - 50% and often bilaterally.
usually a history of preceding respiratory or gastrointestinal viral illness.
(10)
There is
Imaging features:
Bilateral enhancement of the infratemporal facial nerve, often involving the IAC fundus,
labyrinthine segment, geniculate ganglion, tympanic and mastoid segments.
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Fig. 8: Guillain-Barré Syndrome : Bilateral enhancement of the IAC fundus ,
labyrinthine segment, geniculate ganglion, tympanic and mastoid segments of the
facial nerves.
References: Alfred Health - SOUTH YARRA/AU
Bell's palsy
Bell's palsy is a rapidly progressive facial nerve paralysis. It is thought to be due to
reactivation of latent herpes simplex virus in the geniculate ganglion.
Imaging features: Vivid asymmetrical enhancement of the facial nerve, commonly on
either side of the geniculate ganglion - in the fundal and labyrinthine segments. The
infratemporal segment may also be affected.
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Fig. 9: Bell's palsy: Vivid asymmetrical enhancement of the left IAC fundus,
labyrinthine, geniculate ganglion, tympanic and mastoid segments of the facial nerve..
References: Alfred Health - SOUTH YARRA/AU
Neurovascular compression
The facial nerve may be compressed by a vascular loop, usually at its root exit zone in
the cerebellopontine angle cistern, causing hemifacial spasm. The vascular loop may be
the anterior inferior cerebellar artery (most common), posterior inferior cerebellar artery
or vertebral artery.
Less commonly, the facial nerve may be compressed within the internal acoustic canal
(11)
by a vascular loop.
Imaging features: High resolution T2 weighted sequence (FIESTA) demonstrating a
serpigenous vascular loop contacting and displacing the facial nerve, most commonly at
its root exit zone, but could also be in the internal acoustic canal.
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Fig. 10: Neurovascular compression: Long slender right AICA (red arrow) contacting
and displacing the facial nerve (yellow arrow) in the internal acoustic canal causing
hemifacial spasm. A piece of surgical Teflon (blue arrow) has been inserted in between
the AICA and the right facial nerve with good post operative outcome.
References: Alfred Health - SOUTH YARRA/AU
Trauma
Temporal bone fracture
Temporal bone fracture occurs with severe blunt trauma to the skull. Temporal bone
fracture is traditionally described as longitudinal, transverse or mixed type according to
radiographic anatomical involvement. However, there is a newer system which classifies
the temporal bone fracture according to otic capsule violating or sparing in order to predict
clinical sequelae of trauma.
Whilst longitudinal fractures (75-80%) are more common than transverse fractures, facial
nerve injury is reported to occur in only 25% of longitudinal and 40% to 50% of transverse
fractures.
(12)
Fractures that do not violate the otic capsule are much less likely to damage the
cochleovestibular system or the facial nerve, owing to the protective density of the otic
(13)
capsule bone. In Dahiya and colleagues'
study of 55 temporal bone fractures, patients
with otic capsule-violating fractures were more than twice as likely to have facial nerve
injury, 4 times as likely to have CSF leakage, and 7 times as likely to have SNHL than
those with otic capsule-sparing fractures.
Imaging features: Longitudinal fracture typically runs parallel to the petrous pyramid
through the middle ear. Transverse fractures run perpendicular to the petrous ridge,
from the foramen magnum across the petrous pyramid. Transverse fractures often affect
the labyrinthine segment, while longitudinal fractures more often affect the geniculate
ganglion, tympanic and mastoid segment.
Page 14 of 18
Fig. 11: Temporal bone Trauma: Longitudinal temporal bone fracture extending
through the geniculate ganglion and tympanic segment of the facial nerve causing
facial nerve palsy.
References: Alfred Health - SOUTH YARRA/AU
Congenital malformations:
There are multiple congenital anomalies affecting the facial nerve, including facial nerve
canal dehiscences, facial nerve aplasia/hypoplasia, duplicated IAC, and many congenital
syndromes such as Möbius, DiGeorge, Goldenhar, CHARGE, trisomy 13, and trisomy 18.
Page 15 of 18
Fig. 12: Möbius syndrome : Hypoplastic right facial nerve (yellow arrow) and absent
left facial nerve (blue arrow)in a child with bilateral facial and abducens nerves palsy.
References: Dr Yune Kwong, Radiopaedia
Conclusion
Conclusion
Page 16 of 18
Understanding of the anatomy and pathology of the facial nerve will improve one's ability
to diagnose. This article reviews the radiologic findings of several common pathologies
that affect the facial nerve.
Personal information
Pei Fun Kwan
MRI Fellow
Alfred Health
[email protected]
Rosemarie Thomas
Body Fellow
Alfred Health
[email protected]
References
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