MR diagnosis of facial neuritis: diagnostic performance of contrast-enhanced 3D-FLAIR technique compared with contrast-enhanced 3D-T1-fast-field echo with fat suppression

BACKGROUND AND PURPOSE:Current MRI with the CE T1-weighted sequence plays a limited role in the evaluation of facial neuritis due to prominent normal facial nerve enhancement. Our purpose was to retrospectively investigate the usefulness of the CE 3D-FLAIR sequence compared with the CE 3D-T1-FFE sequence in facial neuritis patients.MATERIALS AND METHODS:We assessed 36 consecutive patients who underwent temporal bone MR imaging at 3T for idiopathic facial palsy. Two readers independently reviewed CE 3D-T1-FFE and CE 3D-FLAIR images to determine the degree of enhancement in each of 5 segments of the facial nerve. We compared AUCs using the Z-test, compared diagnostic performance of 2 MR techniques with the McNemar test, and evaluated interobserver agreement. The Pearson χ² test was used for each segment of the facial nerve.RESULTS:The AUC of CE 3D-FLAIR (reader 1, 0.754; reader 2, 0.746) was greater than that of CE 3D-T1-FFE (reader 1, 0.624; reader 2, 0.640; P < .001). The diagnostic sensitivities, specificities, and accuracies were 97.2%, 86.1%, and 91.7%, respectively, for CE 3D-FLAIR, and 100%, 56.9%, and 78.5%, respectively, for CE 3D-T1-FFE. The specificity and accuracy of CE 3D-FLAIR were greater than those of CE 3D-T1-FFE (specificity, P = .029; accuracy, P = .008). The interobserver agreements for CE 3D-FLAIR (κ-value, 0.831) and CE 3D-T1-FFE (κ-value, 0.694) were excellent. Enhancement of the canalicular and anterior genu segments on CE 3D-FLAIR were significantly correlated with the occurrence of facial neuritis (P < .001 for canalicular; P = .032 and 0.020 for anterior genu by reader 1 and reader 2, respectively).CONCLUSIONS:CE 3D-FLAIR can improve the specificity and overall accuracy of MR imaging in patients with idiopathic facial palsy.

MR imaging of patients with facial neuritis is usually not indicated except for patients with facial palsy who have atypical manifestations and those with intractable palsy despite therapy. In most patients, the diagnosis of facial neuritis is clinically evident and EPS confirms this. EPS can also provide prognostic information on outcomes in patients with acute facial palsy. However, the major disadvantage of EPS is its inability to detect diagnostic abnormalies of the nerve distal to the stylomastoid foramen within 1 week of symptom onset.¹Although the potential of MR imaging has been studied as part of the effort to find other helpful diagnostic techniques over the past 20 years,^2–10 its results have been largely disappointing. Gd-DTPA-enhanced T1-weighted spin-echo and 3D spoiled gradient-echo sequences have shown significant limitations in diagnosing and predicting outcomes in patients with facial neuritis; the geniculate ganglion, tympanic, or mastoid segment of the normal facial nerve can be significantly enhanced in up to 76% of patients due to the distribution of arteriovenous plexus along the facial nerve, which, in turn, may inhibit evaluation of the pathologic enhancement of the nerves resulting from breakdown of the blood nerve barrier.^10–12 Thus, MR imaging plays a limited role in the diagnosis and provision of prognostic information of facial neuritis.^3,7Recently, a new isotropic 3D-T2-weighted imaging technique, the 3D turbo spin-echo sequence with variable flip angles (VISTA, sampling perfection with application optimized contrast using different flip angle evolution SPACE], or Cube), was introduced on the 3T MR system.¹³ This sequence uses variable refocusing flip angles to constrain T2 decay over a long echo train, with minimal blurring, and can acquire isotropic resolutions in a clinically acceptable scan time. When applied to the temporal bone pathologies, this 3D-FLAIR sequence had higher SNR and CNR than previous 2D sequences.^14,15 Moreover, the 3D-FLAIR sequence has been shown useful in the diagnosis of mumps-related deafness and sudden sensorineural hearing loss, and for predicting the prognosis of patients with sudden sensorineural hearing loss, which is not usually demonstrated by the conventional MR imaging sequences.^16–18 This ability of the 3D-FLAIR sequence to find minute abnormalities mainly results from the high sensitivity of FLAIR imaging to subtle changes of longitudinal magnetization in the fluid space, which declines with the higher concentration of the contrast agent, different from T1-weighted images.^19,20 The 3D-FLAIR sequence is also known to suppress the signal intensity from the flowing fluid at a velocity exceeding 1.0 cm/s.²¹ With this background information, we retrospectively evaluated 3D-FLAIR images in 20 subjects with normal facial nerve function and found that only 1 subject showed mild enhancement of the anterior genu segment. From the preliminary study, we hypothesized that the pathologic enhancement of facial neuritis may be more accurately imaged on 3D-FLAIR images than on T1-FFE images, without normal enhancement of the arteriovenous plexus along the facial nerve.Therefore, the purpose of this study was to investigate the diagnostic performance of CE 3D-FLAIR images compared with CE 3D-T1-FFE images in patients with facial neuritis.