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Neuroradiology Case of the Week

Case 309

Sara Ann Majewski, MD

Clinical Presentation: A 65-year-old male with Ramsey Hunt syndrome seven years earlier, new Bell's palsy and new mental status changes. History of cirrhosis secondary to nonalcoholic steatohepatitis and being worked up for liver transplant.

Imaging Findings: There is T1 contrast enhancement of the left facial nerve within the internal auditory canal extending anteriorly to the geniculate ganglion. There is also suspicion of enhancement within the petrous portion of the nerve. There is no enhancement or mass effect within the brainstem.

Diagnosis: Bell's Palsy

Discussion: Patients commonly present with acute onset (24 to 48 hours) of facial nerve paralysis. People may be affected at any age and are usually otherwise healthy. There is often a viral prodrome about a week before onset. Symptoms found can include taste alteration, pain in the ipsilateral ear and numbness in the ipsilateral face. Herpes simplex DNA is often recovered from facial nerve specimens. Other etiologic factors may include systemic or central polyneuropathy and immunologic or ischemic factors. Treatment usually consists of acyclovir and steroids. Almost complete denervation may be treated with CN VII decompression from the internal auditory canal fundus to the sylomastoid foramen and must be performed within two weeks for maximal effect. Post-treatment, recovery of nerve function is less with age.
     The facial nerve may normally show enhancement in the geniculate ganglion, horizontal region and descending region. Normal enhancement is seen in the circumneural arteriovenous plexus around the cranial nerve VII.
     Enhancement in CN VII is abnormal in the internal auditory canal, labyrinthine region and parotid gland. The arteriovenous plexus is not surrounding portions of the facial nerve in these regions.
     Patients with Bell's Palsy have enhancement within the facial nerve in the labyrinthine region or at the fundus of the internal auditory canal, the narrowest area of nerve passage. The nerve becomes swollen and compressed in this region. Enlarged, enhancing facial nerve in the tympanic and intramastoid region may also be suspicious for Bell's palsy with fitting patient presentation.
     Many limit imaging to atypical cases of Bell's palsy in which the symptoms last for more than four weeks and progression of symptoms.
     Other differential diagnostic considerations of facial nerve enhancement includes schwannoma, Lyme disease, lymphoma, hemangioma, sarcoidosis, viral neuritis, Ramsay-Hunt syndrome, Guillain Barre and perineural spread of tumor. Other differential diagnoses of facial paralysis include parotid tumors, central nervous system tumors, cerebral infarct and temporal bone fracture.

References:

1. Daniels DL, Czervionke LF, Millen SJ, et al. MR imaging of facial nerve enhancement in Bell palsy or after temporal bone surgery. Radiology 1989; 171: 807. [Medline]
2. Gebarski SS, Telian SA, Niparko JK. Enhancement along the normal facial nerve in the facial canal: MR imaging and anatomic correlation. Radiology 1992; 183: 391. [Medline]
3. Grossman, RI and Yousem. The Requisites Neuroradiology. Mosby: Philadelphia, 2003.
4. Harnsberger, HR, Wiggins, RH, Hudgins, PA, et al. Diagnostic Imaging Head and Neck. Amirsys: Salt Lake City, 2004