Idiopathic facial nerve paralysis: analysis of three tesla MRI images and comparison to 1.5 tesla imaging

Introduction

• Idiopathic facial paralysis (IFP) is the most common cause of sudden onset facial paralysis• May be viral in origin but it pathogensis is unclear and controversial (Linder)• 90% will recover within 3 months• Facial nerve paralysis is associated with significant social, psychological and physical morbitity• Electromyography has prognostic value in determining prognosis but is invasive (Smith) • ENG does not seem to correlate with the appearance of the nerve on MR images • Currently no imaging modality has been proven to provide prognostic information for IFP• The facial nerve is visible on 1.5T images particularly at the geniculate ganglion, but the entire nerve may not be seen.• Despite this ability of visualize the facial nerve, at the present time there is no consensus in the literature regarding the utility of magnetic resonance imaging (MRI) in evaluating patient prog- nosis in IFP (Kress)• The hypothesis was that 3T imaging would:

1) demonstrate improved visualization of the facial nerve when compared to 1.5T images 2) that improved visualization of facial nerve enhancement patterns would provide positive information regarding patient prognosis for facial nerve recovery

Material and Methods

• This study was approved by the UCLA Institutional Review Board for Human Subjects• The case logs for the 3T MRI scanner were reviewed for all patients undergoing studies listed as “IACs/Brain,” “temporal bone,” “IAC/MRA,” “IAC/STROKE,” and “IAC/head and neck”• Patients qualified for investigation if they underwent imaging for “Bell’s palsy” or “facial paralysis”• images were then evaluated by a senior neuroradiologist (C.K.) who was initially blinded to the patients’ histories• Controls were taken from the number of patients who underwent imaging for other otologic complaints such as tinnitus or unilateral hear loss• 3T images were also compared to a series of images obtained for IFP on the 1.5T MRI• T1 pre and post contrasted images were analyzed• The following structures were evaluated for their appearance: • Intrameatal segment • Geniculate ganglion • Labrynithine segment • Tympanic segment • Descending segment • Greater superficial petrosal nerve (GSPN) enhancement • Vidian nerve enhancement • trigeminal enhancement

References

Boné, B., et al., Mechanism of contrast enhancement in breast lesions at MR imaging. Acta Radiol, 1998. 39(5): p. 494-500.Gebarski, S., S. Telian, and J. Niparko, Enhancement along the normal facial nerve in the facial canal: MR imaging and anatomic correlation. Radiology, 1992. 183(2): p. 391-394.Kress, B., et al., Bell Palsy: quantitative analysis of MR imaging data as a method of predicting outcome. Radiology, 2003. 230(2): p. 504-509.Linder, T., W. Bossart, and D. Bodmer, Bell’s palsy and Herpes simplex virus: fact or mystery? Otol Neurotol, 2005 26(1): p. 109-113Smith, I., et al., The prognostic value of facial electroneurography in Bell’s palsy. Clin Otolaryngol Allied Sci, 1994. 19(3): p. 201-203.Tabuchi, T., et al., Vascular permeability to fluorescent substance in human cranial nerves. Ann Otol Rhinol Laryngol, 2002. 111: p. 736-737

Sarah Mowry MD1., Claudia Kirsch MD2., Rinaldo Canalis MD1.1 Division of Otolaryngology-Head and Neck Surgery, 2 Department of Neuroradiology; David Geffin School of Medicine, UCLA, Los Angeles, California

Results

One hundred forty two patients underwent MRI on the 3T scanner for temporal bone pathology between 2005 and 2007. Only 4 patients underwent imaging for IFP. Three of these patients had previous or subsequent imaging on a 1.5 T scanner at our institution. No patient had repeat 3T imaging.

Discussion

• The facial nerve takes a long course through the temporal bone before exiting the stylomastoid foramen

• On 0.5 and 1.5T scanners the areas inflammation/enhancement are most notable at the fundus, geniculate ganglion and the descending portion of the nerve

• In this series of patients on 1.5T scans the nerve was enhancing at in the labyrinthine segment, at the ganglion and in the descending segment. This is in line with other reports in the literature

• On 3T images the normal facial nerve enhances at the root entry zone, within the IAC, at the ganglion and in the descending segment. o These findings have not been previously reported

• Furthermore, 3T imaging detected thickening of the facial nerve, particularly in the descending segment. This thickening has not been noted on 1.5T images

• In this series a high number of patients with clinically normal facial nerve function demonstrated enhancement of the facial nerve on 3T imaging. o This is not typically seen on 1.5T images (Gebarski)

o Gadolinum enhancement is seen in areas of increased blood flow and extravascular fluid collection.

- The enhancement may represent the vascular plexus surrounding the nerve in normal nerve tissues (Tabuchi)

- In inflamed tissue the extravascular fluid space is expanded thus allowing for a greater volume of distribution for the contrast agent

- Increased metabolism of the nerve may increase contrast uptake (Boné) • Further investigation in the form of a prospective study is needed

o To determine the natural progression of enhancement patients with IFP would need multiple repeat images on a 3T MRI at symptom onset, during active recovery and after re turn of function

o This protocol may allow for determining any imaging characteristics that may be prognostic of prolonged or permanent facial weakness

Figure 1 - Normal Control - 3 T MRI Axial & Coronal T1 w images post gadolinium

Figure 1a – Note faint normal enhancement of bilateral facial nerves (CN VII) especially in the horizontal portions

Figure 1b - with faint enhancement in the horizontal facial nerve segments

Figure 1c – With faint normal enhancement of bilateral facial nerves (CN VII) in the descending portions in the bilateral stylomastoid foramens

Figure 1d – with faint normal enhancement of bilateralfacial nerves (CN VII) in the descending segments

Figure 2c – Enhancing right VIIth nerve with a “snake eyes” appearance – en-hancement of the labyrinthine and proxi-mal tympanic segments

Figure 2b – Cornoal image demonstrat-ing enhancing right VIIth nerve in all seg-ments including the fundus, geniculate ganglion, labrythine and tympanic portions

Figure 2a - Demonstrates enhancing right VIIth nerve in all segments includ-ing the fundus, geniculate ganglion, labrythine and tympanic portions

Figure 3a – Enhancement in the fundus of the internal auditory canal, labyrinthine and proximal tymnpanic (horizontal portion) initial imaging study

Figure 3b – Enhancement visible in the tymnpanic (hori-zontal portion) initial imaging

Figure 4a - Enhancement of the nerve in the fundus of the internal auditory ca-nal, labyrinthine and proximal tymnpanic (horizontal portion) - with a “snake eye” appearance

Figure 4b – Nerve visible in the proximal tymnpanic (horizontal portion)

Figure 4c – Arrow pointing to descend-ing portion of enhancing left facial nerve

Figure 5a – Axial image with enhancing left VIIth nerve in the fundus of the internal auditory canal, labyrinthine and proxi-mal tymnpanic (horizontal portion)– compare enhancing left VIIth nerve in this study to Figures 4a-c

Figure 5b – Coronal image with enhancing left VIIth nerve in labyrinthine and proximal tymnpanic (horizontal portion)– compare to 3 Tesla MRI Figures 4a-c

Figure 2 – Axial and Coronal 3 Tesla MRI of Patient # 2, with right sided Bell’s palsy Axial T1w post-gadolinium

Figure 3 – Patient # 3, 1.5 Tesla MRI axial T1w post-gad with enhancing left VIIth nerve

Figure 4 - Patient # 3, follow up imaging on a 3 Tesla MRI axial T1w post-gad with enhancing left VIIth nerve

Figure 5 – Patient # 3, 1.5 Tesla MRI obtained at same time of follow up 3 Tesla exam, axial T1w post-gad