Clinical diagnosis

Case 6

Parts of facial nerve

Meatal (internal acoustic meatus) segment of the facial nerve does not receive Gd-enhancement well in Bell’s palsy.

【Treatment】
The patient received hydrocortisone, glycerol and Valtrex (anti-viral agent), leading to the complete disappearance of the symptom one week later.

【Discussion】
Imaging in typical Bell’s palsy is not usually necessary (1, 2). However, facial nerve palsy can occur in other lesions such as facial nerve schwannoma, hemangioma, meningioma, facial nerve neural tumor spread and temporal bone fracture (1, 3, 4). Gd-enhanced MRI is best for differential diagnosis. In patients with Bell’s palsy, enhancement of facial nerve is typical (2, 5). The parts of the facial nerve that normally enhance in Gd-enhanced MRI are reported to be geniculate ganglion, tympanic segment and mastoid segment due to the presence of surrounding rich circum-neural arteriovenous plexus (2, 5). Facial nerve exits internal auditory canal via Fallopian canal which is the narrowest point in the entire facial nerve canal. Labyrinthine segment of the facial nerve situates inside the Fallopian canal. In Bell’s palsy, the main target part of inflammation due to idiopathic or herpes simplex/zoster infection (6) is geniculate ganglion causing the more dilatation of the circum-neural arteriovenous and the facial nerve compression at the swollen labyrinthine (Fallopian) segment, which leads to enhancement of labyrinthine segment (2, 5). In our case, the asymmetric marked enhancement of the labirinthene (Fallopian) segment, geniculate ganglion tympanic segment and mastoid segment of the impaired left facial nerve, were found, leading to the diagnosis of Bell’s palsy. Greater superficial petrosal nerve which innervates lacrima gland branches from geniculate ganglion, chorda tympani nerve which innervates submandibular gland and anterior two thirds tongue taste sensation branches from tympanic segment, stapedius nerve which innervates stapedius muscle to accommodate to a big sound branches from tympanic segment and mastoid segment itself innervates motor roots for facial muscles. The facial nerve finally exits the facial canal via the stylomastoid foramen..Our case suffered from excessive tears, mouth-water after eating, impaired taste sensation and facial muscle spasm. Gadolinium (Gd) induces the shortening effect of T1 values. In case of Gd-enhanced MRI for detecting the enhancement of facial nerve, a sequence of T1WI with fat-suppression might be more preferable to that of T1WI without because fat-suppression induces the clearer contrast of the increase of signal intensity. In our case, the image of Gd-enhanced MRI with fat-suppression depicted the marked contrast enhancement of the impaired left facial nerve.

【Summary】
A nineteen-year-old female with facial nerve palsy received Gd-enhanced MRI with fat suppression T1WI which showed marked enhancement of the labirinthene (Fallopian) segment, the geniculate ganglion, the tympanic segment and the mastoid segment of the impaired left facial nerve, leading to diagnosis of Bell’s palsy.

【References】
1.Baugh RF et al. Clinical practice guideline: Bell's palsy.Otolaryngol Head Neck Surg. 2013 ;149:1-27. doi: 10.1177/0194599813505967.
2.Belvèze P et al. Magnetic Resonance Imaging in Facial Bell's Palsy. Ann Otolaryngol Chir Cervicofac. 2002 ;119:81-88.
3.Gilchrist JM. Seventh cranial neuropathy. Semin Neurol. 2009;29:5-13. doi: 10.1055/s-0028-1124018. Epub 2009 Feb 12
4.Achong DM et al. Facial paralysis secondary to extensive perineural spread of adenocarcinoma of the parotid gland identified by PET/CT.Clin Nucl Med. 2016 Jan 28. [Epub ahead of print]
5.Suzuki F, et al. Herpes virus reactivation and gadolinium-enhanced magnetic resonance imaging in patients with facial palsy. Otol Neurotol.2001 ;22:549-53.
6.Fujiwara T et al. Facial paralysis induced by ear inoculation of herpes simplex virus in rat. Auris Nasus Larynx. 2016 Apr 16. pii: S0385-8146(16)30111-0. doi: 10.1016/j.anl.2016.04.002. [Epub ahead of print]

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2016.05.18