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FACIAL NERVE PATHOLOGIES AND IMAGING CHARACTERISTICS A Mohandas, M Haider, M Le, T Khairalseed, K Shah Detroit Medical Center/Wayne State University eEdE-154 DISCLOSURES • Aravind Narayan Mohandas – nothing to disclose. • Maera Haider – nothing to disclose. • Mark Le – nothing to disclose. • Tagwa Khairalseed – nothing to disclose. • Kamran Shah – nothing to disclose. INTRODUCTION • The facial nerve (FN) has a complex course which makes it’s assessment during imaging challenging. • Adequate understanding of it’s anatomy will facilitate assessment. • The aim of the presentation is to review the normal anatomy with the help of CT and MRI and to review imaging characteristics of pathological entities differentiated along etiological origin. ORIGIN Nucleus Function Motor Nucleus Motor supply to muscles of facial expression Superior salivary nucleus Parasympathetic supply to the major salivary glands and lacrimal gland Nucleus of the tractus solitarius Receives taste sensation from the anterior two thirds of the tongue. ORIGIN (CONT’D) T2 images with illustrations depicting the origin of the FN in the pons. SEGMENTS – CISTERNAL • Cisternal segment emerges from the pons parallel and medial to the vestibulocochlear nerve. • Nerve of Wrisberg (nervus intermedius) carries parasympathetic secretomotor fibres from the superior salivary nucleus and relays taste sensation from the anterior 2/3rds of the tongue to the nucleus of tractus solitarius. • Nerve of Wrisberg joins the facial nerve as it enters the internal auditory canal. SEGMENTS – CANNALICULAR • Cannalicular or meatal segment is the portion of the FN within the internal auditory canal. • Located in the anterosuperior quadrant of the internal auditory canal. • Related medially to the vestibulocochlear nerve. SEGMENTS – LABRYNTHINE • Labrynthine segment courses between the cochlea and vestibule. • Anterior genu – FN bends posteriorly to continue as the tympanic segment. • Geniculate ganglion – located at the junction of the labrynthine and tympanic segments of the facial nerve in front of the anterior genu. • Greater superficial petrosal nerve arises from the geniculate ganglion and supplies the lacrimal glands. • Geniculate ganglion also gives rise to lesser and external petrosal nerves. SEGMENTS – TYMPANIC • Continuation of the FN from the anterior genu in the fallopian canal. • Courses posteriorly beneath the lateral semicircular canal. • After travelling a short distance posterior to the pyramidal eminence the FN turns inferiorly forming the posterior genu and continues as the descending segment. SEGMENTS – DESCENDING • The descending or mastoid segment continues after the FN forms the posterior genu within the fallopian or facial canal. • Emerges from the temporal bone and fallopian canal through the stylomastoid foramen. • Nerve to stapedius and the chorda tympani branch, which carries taste sensation from the anterior 2/3rd of tongue, are branches from this segment. PATHOLOGICAL ENTITIES • Demyelinating disorders. • • Infections and inflammations. • • Multiple sclerosis. Sarcoidosis, Bell’s palsy, fungal infections. Neoplasms. • Benign. • Schwannoma, hemangioma . • Malignant. • Perineural spread of head and neck cancers . • Trauma. • • Temporal bone fractures Miscellaneous • Vascular loop syndrome, arachnoid cyst. MULTIPLE SCLEROSIS • Demyelinating lesions in the infratentorial, juxtacortical and periventricular regions seen as FLAIR hyperintensities. • Isolated cranial nerve involvement may occur in 10% of cases [1]. • Facial nerve affected in 4% of cases [1]. • Only half of these cases have MRI findings in the pons [1]. FLAIR image shows demyelinating lesions in the lower pons in the region of the right facial colliculus (red arrow) including the facial nerve tract and abducens nucleus and in the left corticospinal tract (blue arrow). SARCOIDOSIS • Granulomatous inflammation where neurological involvement occurs in 5-15% of cases [2]. • Variable appearance mimicking other diseases with both supra and infratentorial involvement. • T2 hyperintense lesions which enhance along with leptomeningeal enhancement. (A) FLAIR image shows diffuse hyperintense lesions in the pons, cerebellum and bilateral facial nerves (red arrows). SARCOIDOSIS • Facial nerve is the most commonly affected cranial nerve [3]. • Heerfordt syndrome – variant of sarcoidosis with fever, parotid enlargement, facial palsy and anterior uveitis. (B) Post contrast image shows intense nodular enhancement in the pons, cerebellum and bilateral facial nerves (red arrows). BELL’S PALSY • Idiopathic facial neuropathy. • Reactivation of herpes simplex virus from geniculate ganglion considered as possible cause. • Tympanic and mastoid segments normally enhance slightly due to rich venous plexus in temporal bone. • Slight enhancement of the intracannalicular and labrynthine segments is normal due to rich venous plexus within the temporal bone. Post contrast image shows abnormal enhancement of the cannalicular, labrynthine segment and anterior genu (red arrow) of the right facial nerve. Contiguous enhancement of the tympanic segment also noted which is normal. FUNGAL INFECTIONS • Fungal infections of the brain occur particularly in immuno-compromised patients. • May result from hematogenous spread or angiotropic and perineural spread from adjacent sites. (A) Post contrast image show abscess forming blastomycosis impinging on the origin of the left facial nerve at the cerebellopontine angle (red arrow). FUNGAL INFECTION • Fungal malignant external otitis has a predilection for FN involvement (50%) [4]. • Organisms – Aspergillus, Mucomycosis, Blastomycosis, Candida, etc. (B) T2 weighted images show abscess forming blastomycosis impinging on the origin of the left facial nerve at the cerebellopontine angle (red arrow). SCHWANNOMA • Most common primary neoplasm of facial nerve. • Multisegmental involvement with geniculate ganglion most commonly affected [5]. • Iso to hypointense on T1, iso to hyperintense on T2 with homogenous enhancement. • Cystic change in 20% of cases [5]. • CT may show bone remodelling and scalloping if intratemporal in location. (A) CT temporal bone - schwannoma of descending segment expanding facial canal (red arrow). (B) Post contrast MRI - enhancement of the mass (green arrow). Blue arrow – Internal jugular vein. SCHWANNOMA (A) & (B) Axial CT images show schwannoma of the right FN within the deep lobe of the right parotid gland (red arrow) with resultant facial palsy and right buccinator (blue arrow) and platysma (yellow arrow) atrophy. SCHWANNOMA Post contrast T1 images emphasizing multi-segmental involvement of the FN (red arrows). HEMANGIOMA • Venous vascular malformation of the facial nerve. • Predeliction for the geniculate ganglion. • Facial palsy out of proportion to the size of the lesion. • Heterogeneously hyperintense T2 mass with punctate foci of hypointensity which enhances. (A) Iso to slightly hyperintense T1 lesion in the geniculate ganglion of left facial nerve (red arrow). (B) T2 hyperintense mass from left facial nerve geniculate ganglion (blue arrow) PERINEURAL SPREAD OF TUMOR • Metastatic tumor spread through perineurium or endoneurium to non contiguous areas. • Associated with squamous cell carcinoma of head and neck and parotid malignancy. • Incidence of approximately 10-30% in parotid malignancy [6]. • Most common in adenoid cystic carcinoma of the parotid (50%) [7]. • Neural thickening, enhancement and canal and foraminal widening. PERINEURAL SPREAD (A) &(B) Pre and post contrast T1 images shows multiple masses in the left parotid (blue arrow) extending along the FN into the digastric groove (red arrow) with homogenous enhancement. (C) Coronal post contrast image shows expansion of the facial canal and enhancement of the descending segment (yellow arrow). PERINEURAL SPREAD (A) Axial CT shows expansion of the left facial canal (red arrow). (B) and (C) Post contrast axial MRI images show enhancing descending portion of the left FN (red arrow) and geniculate ganglion (blue arrow). TEMPORAL BONE FRACTURES • Due to motor vehicle collision, assault and falls. • Up to 20% of patients with craniofacial trauma have temporal bone fractures [8]. • Complex course of FN within the temporal bone makes it vulnerable to injury at multiple points. • FN injury occurs in 5-10% of patients with temporal bone fractures [8]. • Geniculate ganglion is the most commonly injured part [8]. (A) Axial CT shows comminuted fracture of the temporal bone affecting the tympanic (red arrow) and descending (blue arrow) segments. TEMPORAL BONE FRACTURES (B) & (C) Coronal CT shows transverse fracture (yellow arrow) crossing the geniculate fossa and lateral semi circular canal resulting in it’s lateral displacement (green arrow). VASCULAR LOOP SYNDROME • Compression of FN by a vessel is an accepted cause of hemifacial spasm. • Trigeminal nerve is the most commonly affected cranial nerve followed by FN involvement with an incidence of about 0.8/100,000 [9]. • Presents with spasm of the eyelids initially and then spreads downwards. • MRI is excellent at demonstrating vascular compression of the FN. T2 image showing a dolichoectatic left vertebral artery (blue arrow) compressing the left FN at its root of exit and causing mass effect on the adjacent pons (red arrow). VASCULAR LOOP SYNDROME • Root of exit of FN is its weakest point and most susceptible to compression. • The most common offending vessel causing hemifacial spasm is the posteroinferior cerebellar artery (70%) followed by the vertebral artery (41%) and anteroinferior cerebellar artery (28%) [10]. • The frequency of multiple offending vessels in the same patient is high (38%) [10]. FLAIR image shows compression of the left FN at its root of exit (red arrow) by the dolichoectatic left vertebral artery (blue arrow). ARACHNOID CYST • Arachnoid cyst at the CP angle is usually asymptomatic and developmental arising from splitting of the arachnoid and contains cerebrospinal fluid. • Rare cause of hemifacial spasm. • T2 and FLAIR sequences used to demonstrate properties of cerebrospinal fluid within the cyst. T2 (A) and FLAIR (B) images showing mass at the left cerebellopontine angle with properties of cerebrospinal fluid (red arrows). REFERENCES 1. Zadro, I., et al., Isolated cranial nerve palsies in multiple sclerosis. Clin Neurol Neurosurg, 2008. 110(9): p. 886-8. 2. Segal, B.M., Neurosarcoidosis: diagnostic approaches and therapeutic strategies. Curr Opin Neurol, 2013. 26(3): p. 307-13. 3. Pickuth, D., R.P. Spielmann, and S.H. Heywang-Kobrunner, Role of radiology in the diagnosis of neurosarcoidosis. Eur Radiol, 2000. 10(6): p. 941-4. 4. Hamzany, Y., et al., Fungal malignant external otitis. J Infect, 2011. 62(3): p. 226-31. 5. Thompson, A.L., et al., Magnetic resonance imaging of facial nerve schwannoma. Laryngoscope, 2009. 119(12): p. 2428-36. 6. Terhaard, C.H., et al., Salivary gland carcinoma: independent prognostic factors for locoregional control, distant metastases, and overall survival: results of the Dutch head and neck oncology cooperative group. Head Neck, 2004. 26(8): p. 681-92; discussion 692-3. 7. Carlson, M.L., et al., Occult Temporal Bone Facial Nerve Involvement by Parotid Malignancies with Perineural Spread. Otolaryngol Head Neck Surg, 2015. 153(3): p. 385-91. 8. Kennedy, T.A., G.D. Avey, and L.R. Gentry, Imaging of temporal bone trauma. Neuroimaging Clin N Am, 2014. 24(3): p. 46786, viii. 9. Auger, R.G. and J.P. Whisnant, Hemifacial spasm in Rochester and Olmsted County, Minnesota, 1960 to 1984. Arch Neurol, 1990. 47(11): p. 1233-4. 10. Sherif Elaini, J.M., Arnaud Deveze, Nadine Girard, Magnetic resonance imaging criteria in vascular compression syndrome. The Egyptian Journal of Otolaryngology, 2013. 29(1): p. 10-15.