Morphometric evaluation of facial and vestibulocochlear nerves using magnetic resonance imaging: comparison of Menière's disease ears with normal hearing ears.

Loss of neural structures (such as hair cells or neurones within the spiral ganglion) has been proposed to be involved in Menière's disease (MD) (Spoendlin et al. Acta oto-laryngologica Supplementum 499:1-21, 1; Merchant et al. Eur Arch Oto-Rhino-Laryngol Off J Eur Feder Oto-Rhino-Laryngol Soc (EUFOS) Affil German Soc Oto-Rhino-Laryngol Head Neck Surg 252(2):63-75, 2; Tsuji et al. Ann Otol Rhinol Laryngol Suppl 81:26-31, 3; Kariya, Otol Neurotol Off Publ Am Otol Soc Am Neurotol Soc Eur Acad Otol Neurotol 28(8):1063-1068, 4; Megerian Laryngoscope 115(9):1525-1535, 5) but this has yet to be confirmed. Therefore, the aim of this study was to investigate morphometric changes of VIIth and VIIIth cranial nerve in MD. MD is characterized by episodic vertigo, tinnitus, fluctuating hearing loss, and aural fullness. The exact pathophysiological mechanisms involved such as viral infections, autoimmune processes, genetic predisposition, cellular apoptosis, and oxidative stress are still not clear. Using a T2-weighted 3D-GE "constructive interference in steady state" (CISS) 3T magnetic resonance imaging (MRI) sequence, we evaluated the properties of the VIIth and VIIIth cranial nerves as they passed from the cerebellopontine angle to the inner ear modiolus. 21 patients with MD were examined along with 39 normal controls. Bidirectional nerve diameters and cross-sectional areas (CSA) were measured in a transverse plane. The comparison of study and control group showed statistically significant (P < 0.000595 after Bonferroni correction) differences between the CSA measurements. The facial, cochlear, superior vestibular, and inferior vestibular nerves (FN, CN, SVN, IVN) of MD patients were significantly larger than those of the control group, both on the MD-affected side and on the healthy side. Thus for example, the cochlear nerve CSA measurements were 0.69 ± 0.14 mm (P < 0.0001) in the affected ears of the unilateral MD group, 0.70 ± 0.12 mm (P < 0.0001) in the affected ears of the cohort including the bilateral MD group, 0.71 ± 0.13 mm (P < 0.0001) in the non-affected ears of the MD patients, as compared to 0.46 ± 0.14 mm in the control group. The perpendicular nerve diameters were found to vary according to site of measurement and type of measurement used. For example a statistically significant enlargement of the short diameter measurements of the SVN at the level of the meatus was found, but not of long diameter measurements at the same site. Although cellular death would theoretically be expected to lead to a decreased nerve thickness, our data showed a swelling of cranial nerves VII and VIII within the study group compared to our normal hearing control group. The similar reaction of the facial nerve supports mediator-based theories of MD pathophysiology.